linux/drivers/char/tty_ldisc.c

898 lines
22 KiB

tty-ldisc: turn ldisc user count into a proper refcount By using the user count for the actual lifetime rules, we can get rid of the silly "wait_for_idle" logic, because any busy ldisc will automatically stay around until the last user releases it. This avoids a host of odd issues, and simplifies the code. So now, when the last ldisc reference is dropped, we just release the ldisc operations struct reference, and free the ldisc. It looks obvious enough, and it does work for me, but the counting _could_ be off. It probably isn't (bad counting in the new version would generally imply that the old code did something really bad, like free an ldisc with a non-zero count), but it does need some testing, and preferably somebody looking at it. With this change, both 'tty_ldisc_put()' and 'tty_ldisc_deref()' are just aliases for the new ref-counting 'put_ldisc()'. Both of them decrement the ldisc user count and free it if it goes down to zero. They're identical functions, in other words. But the reason they still exist as sepate functions is that one of them was exported (tty_ldisc_deref) and had a stupid name (so I don't want to use it as the main name), and the other one was used in multiple places (and I didn't want to make the patch larger just to rename the users). In addition to the refcounting, I did do some minimal cleanup. For example, now "tty_ldisc_try()" actually returns the ldisc it got under the lock, rather than returning true/false and then the caller would look up the ldisc again (now without the protection of the lock). That said, there's tons of dubious use of 'tty->ldisc' without obviously proper locking or refcounting left. I expressly did _not_ want to try to fix it all, keeping the patch minimal. There may or may not be bugs in that kind of code, but they wouldn't be _new_ bugs. That said, even if the bugs aren't new, the timing and lifetime will change. For example, some silly code may depend on the 'tty->ldisc' pointer not changing because they hold a refcount on the 'ldisc'. And that's no longer true - if you hold a ref on the ldisc, the 'ldisc' itself is safe, but tty->ldisc may change. So the proper locking (remains) to hold tty->ldisc_mutex if you expect tty->ldisc to be stable. That's not really a _new_ rule, but it's an example of something that the old code might have unintentionally depended on and hidden bugs. Whatever. The patch _looks_ sensible to me. The only users of ldisc->users are: - get_ldisc() - atomically increment the count - put_ldisc() - atomically decrements the count and releases if zero - tty_ldisc_try_get() - creates the ldisc, and sets the count to 1. The ldisc should then either be released, or be attached to a tty. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Tested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Tested-by: Sergey Senozhatsky <sergey.senozhatsky@mail.by> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-08-03 11:11:19 -07:00
tty-ldisc: turn ldisc user count into a proper refcount By using the user count for the actual lifetime rules, we can get rid of the silly "wait_for_idle" logic, because any busy ldisc will automatically stay around until the last user releases it. This avoids a host of odd issues, and simplifies the code. So now, when the last ldisc reference is dropped, we just release the ldisc operations struct reference, and free the ldisc. It looks obvious enough, and it does work for me, but the counting _could_ be off. It probably isn't (bad counting in the new version would generally imply that the old code did something really bad, like free an ldisc with a non-zero count), but it does need some testing, and preferably somebody looking at it. With this change, both 'tty_ldisc_put()' and 'tty_ldisc_deref()' are just aliases for the new ref-counting 'put_ldisc()'. Both of them decrement the ldisc user count and free it if it goes down to zero. They're identical functions, in other words. But the reason they still exist as sepate functions is that one of them was exported (tty_ldisc_deref) and had a stupid name (so I don't want to use it as the main name), and the other one was used in multiple places (and I didn't want to make the patch larger just to rename the users). In addition to the refcounting, I did do some minimal cleanup. For example, now "tty_ldisc_try()" actually returns the ldisc it got under the lock, rather than returning true/false and then the caller would look up the ldisc again (now without the protection of the lock). That said, there's tons of dubious use of 'tty->ldisc' without obviously proper locking or refcounting left. I expressly did _not_ want to try to fix it all, keeping the patch minimal. There may or may not be bugs in that kind of code, but they wouldn't be _new_ bugs. That said, even if the bugs aren't new, the timing and lifetime will change. For example, some silly code may depend on the 'tty->ldisc' pointer not changing because they hold a refcount on the 'ldisc'. And that's no longer true - if you hold a ref on the ldisc, the 'ldisc' itself is safe, but tty->ldisc may change. So the proper locking (remains) to hold tty->ldisc_mutex if you expect tty->ldisc to be stable. That's not really a _new_ rule, but it's an example of something that the old code might have unintentionally depended on and hidden bugs. Whatever. The patch _looks_ sensible to me. The only users of ldisc->users are: - get_ldisc() - atomically increment the count - put_ldisc() - atomically decrements the count and releases if zero - tty_ldisc_try_get() - creates the ldisc, and sets the count to 1. The ldisc should then either be released, or be attached to a tty. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Tested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Tested-by: Sergey Senozhatsky <sergey.senozhatsky@mail.by> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-08-03 11:11:19 -07:00
tty-ldisc: turn ldisc user count into a proper refcount By using the user count for the actual lifetime rules, we can get rid of the silly "wait_for_idle" logic, because any busy ldisc will automatically stay around until the last user releases it. This avoids a host of odd issues, and simplifies the code. So now, when the last ldisc reference is dropped, we just release the ldisc operations struct reference, and free the ldisc. It looks obvious enough, and it does work for me, but the counting _could_ be off. It probably isn't (bad counting in the new version would generally imply that the old code did something really bad, like free an ldisc with a non-zero count), but it does need some testing, and preferably somebody looking at it. With this change, both 'tty_ldisc_put()' and 'tty_ldisc_deref()' are just aliases for the new ref-counting 'put_ldisc()'. Both of them decrement the ldisc user count and free it if it goes down to zero. They're identical functions, in other words. But the reason they still exist as sepate functions is that one of them was exported (tty_ldisc_deref) and had a stupid name (so I don't want to use it as the main name), and the other one was used in multiple places (and I didn't want to make the patch larger just to rename the users). In addition to the refcounting, I did do some minimal cleanup. For example, now "tty_ldisc_try()" actually returns the ldisc it got under the lock, rather than returning true/false and then the caller would look up the ldisc again (now without the protection of the lock). That said, there's tons of dubious use of 'tty->ldisc' without obviously proper locking or refcounting left. I expressly did _not_ want to try to fix it all, keeping the patch minimal. There may or may not be bugs in that kind of code, but they wouldn't be _new_ bugs. That said, even if the bugs aren't new, the timing and lifetime will change. For example, some silly code may depend on the 'tty->ldisc' pointer not changing because they hold a refcount on the 'ldisc'. And that's no longer true - if you hold a ref on the ldisc, the 'ldisc' itself is safe, but tty->ldisc may change. So the proper locking (remains) to hold tty->ldisc_mutex if you expect tty->ldisc to be stable. That's not really a _new_ rule, but it's an example of something that the old code might have unintentionally depended on and hidden bugs. Whatever. The patch _looks_ sensible to me. The only users of ldisc->users are: - get_ldisc() - atomically increment the count - put_ldisc() - atomically decrements the count and releases if zero - tty_ldisc_try_get() - creates the ldisc, and sets the count to 1. The ldisc should then either be released, or be attached to a tty. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Tested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Tested-by: Sergey Senozhatsky <sergey.senozhatsky@mail.by> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-08-03 11:11:19 -07:00
tty-ldisc: turn ldisc user count into a proper refcount By using the user count for the actual lifetime rules, we can get rid of the silly "wait_for_idle" logic, because any busy ldisc will automatically stay around until the last user releases it. This avoids a host of odd issues, and simplifies the code. So now, when the last ldisc reference is dropped, we just release the ldisc operations struct reference, and free the ldisc. It looks obvious enough, and it does work for me, but the counting _could_ be off. It probably isn't (bad counting in the new version would generally imply that the old code did something really bad, like free an ldisc with a non-zero count), but it does need some testing, and preferably somebody looking at it. With this change, both 'tty_ldisc_put()' and 'tty_ldisc_deref()' are just aliases for the new ref-counting 'put_ldisc()'. Both of them decrement the ldisc user count and free it if it goes down to zero. They're identical functions, in other words. But the reason they still exist as sepate functions is that one of them was exported (tty_ldisc_deref) and had a stupid name (so I don't want to use it as the main name), and the other one was used in multiple places (and I didn't want to make the patch larger just to rename the users). In addition to the refcounting, I did do some minimal cleanup. For example, now "tty_ldisc_try()" actually returns the ldisc it got under the lock, rather than returning true/false and then the caller would look up the ldisc again (now without the protection of the lock). That said, there's tons of dubious use of 'tty->ldisc' without obviously proper locking or refcounting left. I expressly did _not_ want to try to fix it all, keeping the patch minimal. There may or may not be bugs in that kind of code, but they wouldn't be _new_ bugs. That said, even if the bugs aren't new, the timing and lifetime will change. For example, some silly code may depend on the 'tty->ldisc' pointer not changing because they hold a refcount on the 'ldisc'. And that's no longer true - if you hold a ref on the ldisc, the 'ldisc' itself is safe, but tty->ldisc may change. So the proper locking (remains) to hold tty->ldisc_mutex if you expect tty->ldisc to be stable. That's not really a _new_ rule, but it's an example of something that the old code might have unintentionally depended on and hidden bugs. Whatever. The patch _looks_ sensible to me. The only users of ldisc->users are: - get_ldisc() - atomically increment the count - put_ldisc() - atomically decrements the count and releases if zero - tty_ldisc_try_get() - creates the ldisc, and sets the count to 1. The ldisc should then either be released, or be attached to a tty. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Tested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Tested-by: Sergey Senozhatsky <sergey.senozhatsky@mail.by> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-08-03 11:11:19 -07:00
tty-ldisc: turn ldisc user count into a proper refcount By using the user count for the actual lifetime rules, we can get rid of the silly "wait_for_idle" logic, because any busy ldisc will automatically stay around until the last user releases it. This avoids a host of odd issues, and simplifies the code. So now, when the last ldisc reference is dropped, we just release the ldisc operations struct reference, and free the ldisc. It looks obvious enough, and it does work for me, but the counting _could_ be off. It probably isn't (bad counting in the new version would generally imply that the old code did something really bad, like free an ldisc with a non-zero count), but it does need some testing, and preferably somebody looking at it. With this change, both 'tty_ldisc_put()' and 'tty_ldisc_deref()' are just aliases for the new ref-counting 'put_ldisc()'. Both of them decrement the ldisc user count and free it if it goes down to zero. They're identical functions, in other words. But the reason they still exist as sepate functions is that one of them was exported (tty_ldisc_deref) and had a stupid name (so I don't want to use it as the main name), and the other one was used in multiple places (and I didn't want to make the patch larger just to rename the users). In addition to the refcounting, I did do some minimal cleanup. For example, now "tty_ldisc_try()" actually returns the ldisc it got under the lock, rather than returning true/false and then the caller would look up the ldisc again (now without the protection of the lock). That said, there's tons of dubious use of 'tty->ldisc' without obviously proper locking or refcounting left. I expressly did _not_ want to try to fix it all, keeping the patch minimal. There may or may not be bugs in that kind of code, but they wouldn't be _new_ bugs. That said, even if the bugs aren't new, the timing and lifetime will change. For example, some silly code may depend on the 'tty->ldisc' pointer not changing because they hold a refcount on the 'ldisc'. And that's no longer true - if you hold a ref on the ldisc, the 'ldisc' itself is safe, but tty->ldisc may change. So the proper locking (remains) to hold tty->ldisc_mutex if you expect tty->ldisc to be stable. That's not really a _new_ rule, but it's an example of something that the old code might have unintentionally depended on and hidden bugs. Whatever. The patch _looks_ sensible to me. The only users of ldisc->users are: - get_ldisc() - atomically increment the count - put_ldisc() - atomically decrements the count and releases if zero - tty_ldisc_try_get() - creates the ldisc, and sets the count to 1. The ldisc should then either be released, or be attached to a tty. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Tested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Tested-by: Sergey Senozhatsky <sergey.senozhatsky@mail.by> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-08-03 11:11:19 -07:00
tty-ldisc: turn ldisc user count into a proper refcount By using the user count for the actual lifetime rules, we can get rid of the silly "wait_for_idle" logic, because any busy ldisc will automatically stay around until the last user releases it. This avoids a host of odd issues, and simplifies the code. So now, when the last ldisc reference is dropped, we just release the ldisc operations struct reference, and free the ldisc. It looks obvious enough, and it does work for me, but the counting _could_ be off. It probably isn't (bad counting in the new version would generally imply that the old code did something really bad, like free an ldisc with a non-zero count), but it does need some testing, and preferably somebody looking at it. With this change, both 'tty_ldisc_put()' and 'tty_ldisc_deref()' are just aliases for the new ref-counting 'put_ldisc()'. Both of them decrement the ldisc user count and free it if it goes down to zero. They're identical functions, in other words. But the reason they still exist as sepate functions is that one of them was exported (tty_ldisc_deref) and had a stupid name (so I don't want to use it as the main name), and the other one was used in multiple places (and I didn't want to make the patch larger just to rename the users). In addition to the refcounting, I did do some minimal cleanup. For example, now "tty_ldisc_try()" actually returns the ldisc it got under the lock, rather than returning true/false and then the caller would look up the ldisc again (now without the protection of the lock). That said, there's tons of dubious use of 'tty->ldisc' without obviously proper locking or refcounting left. I expressly did _not_ want to try to fix it all, keeping the patch minimal. There may or may not be bugs in that kind of code, but they wouldn't be _new_ bugs. That said, even if the bugs aren't new, the timing and lifetime will change. For example, some silly code may depend on the 'tty->ldisc' pointer not changing because they hold a refcount on the 'ldisc'. And that's no longer true - if you hold a ref on the ldisc, the 'ldisc' itself is safe, but tty->ldisc may change. So the proper locking (remains) to hold tty->ldisc_mutex if you expect tty->ldisc to be stable. That's not really a _new_ rule, but it's an example of something that the old code might have unintentionally depended on and hidden bugs. Whatever. The patch _looks_ sensible to me. The only users of ldisc->users are: - get_ldisc() - atomically increment the count - put_ldisc() - atomically decrements the count and releases if zero - tty_ldisc_try_get() - creates the ldisc, and sets the count to 1. The ldisc should then either be released, or be attached to a tty. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Tested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Tested-by: Sergey Senozhatsky <sergey.senozhatsky@mail.by> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-08-03 11:11:19 -07:00
tty-ldisc: turn ldisc user count into a proper refcount By using the user count for the actual lifetime rules, we can get rid of the silly "wait_for_idle" logic, because any busy ldisc will automatically stay around until the last user releases it. This avoids a host of odd issues, and simplifies the code. So now, when the last ldisc reference is dropped, we just release the ldisc operations struct reference, and free the ldisc. It looks obvious enough, and it does work for me, but the counting _could_ be off. It probably isn't (bad counting in the new version would generally imply that the old code did something really bad, like free an ldisc with a non-zero count), but it does need some testing, and preferably somebody looking at it. With this change, both 'tty_ldisc_put()' and 'tty_ldisc_deref()' are just aliases for the new ref-counting 'put_ldisc()'. Both of them decrement the ldisc user count and free it if it goes down to zero. They're identical functions, in other words. But the reason they still exist as sepate functions is that one of them was exported (tty_ldisc_deref) and had a stupid name (so I don't want to use it as the main name), and the other one was used in multiple places (and I didn't want to make the patch larger just to rename the users). In addition to the refcounting, I did do some minimal cleanup. For example, now "tty_ldisc_try()" actually returns the ldisc it got under the lock, rather than returning true/false and then the caller would look up the ldisc again (now without the protection of the lock). That said, there's tons of dubious use of 'tty->ldisc' without obviously proper locking or refcounting left. I expressly did _not_ want to try to fix it all, keeping the patch minimal. There may or may not be bugs in that kind of code, but they wouldn't be _new_ bugs. That said, even if the bugs aren't new, the timing and lifetime will change. For example, some silly code may depend on the 'tty->ldisc' pointer not changing because they hold a refcount on the 'ldisc'. And that's no longer true - if you hold a ref on the ldisc, the 'ldisc' itself is safe, but tty->ldisc may change. So the proper locking (remains) to hold tty->ldisc_mutex if you expect tty->ldisc to be stable. That's not really a _new_ rule, but it's an example of something that the old code might have unintentionally depended on and hidden bugs. Whatever. The patch _looks_ sensible to me. The only users of ldisc->users are: - get_ldisc() - atomically increment the count - put_ldisc() - atomically decrements the count and releases if zero - tty_ldisc_try_get() - creates the ldisc, and sets the count to 1. The ldisc should then either be released, or be attached to a tty. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Tested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Tested-by: Sergey Senozhatsky <sergey.senozhatsky@mail.by> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-08-03 11:11:19 -07:00
tty-ldisc: turn ldisc user count into a proper refcount By using the user count for the actual lifetime rules, we can get rid of the silly "wait_for_idle" logic, because any busy ldisc will automatically stay around until the last user releases it. This avoids a host of odd issues, and simplifies the code. So now, when the last ldisc reference is dropped, we just release the ldisc operations struct reference, and free the ldisc. It looks obvious enough, and it does work for me, but the counting _could_ be off. It probably isn't (bad counting in the new version would generally imply that the old code did something really bad, like free an ldisc with a non-zero count), but it does need some testing, and preferably somebody looking at it. With this change, both 'tty_ldisc_put()' and 'tty_ldisc_deref()' are just aliases for the new ref-counting 'put_ldisc()'. Both of them decrement the ldisc user count and free it if it goes down to zero. They're identical functions, in other words. But the reason they still exist as sepate functions is that one of them was exported (tty_ldisc_deref) and had a stupid name (so I don't want to use it as the main name), and the other one was used in multiple places (and I didn't want to make the patch larger just to rename the users). In addition to the refcounting, I did do some minimal cleanup. For example, now "tty_ldisc_try()" actually returns the ldisc it got under the lock, rather than returning true/false and then the caller would look up the ldisc again (now without the protection of the lock). That said, there's tons of dubious use of 'tty->ldisc' without obviously proper locking or refcounting left. I expressly did _not_ want to try to fix it all, keeping the patch minimal. There may or may not be bugs in that kind of code, but they wouldn't be _new_ bugs. That said, even if the bugs aren't new, the timing and lifetime will change. For example, some silly code may depend on the 'tty->ldisc' pointer not changing because they hold a refcount on the 'ldisc'. And that's no longer true - if you hold a ref on the ldisc, the 'ldisc' itself is safe, but tty->ldisc may change. So the proper locking (remains) to hold tty->ldisc_mutex if you expect tty->ldisc to be stable. That's not really a _new_ rule, but it's an example of something that the old code might have unintentionally depended on and hidden bugs. Whatever. The patch _looks_ sensible to me. The only users of ldisc->users are: - get_ldisc() - atomically increment the count - put_ldisc() - atomically decrements the count and releases if zero - tty_ldisc_try_get() - creates the ldisc, and sets the count to 1. The ldisc should then either be released, or be attached to a tty. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Tested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Tested-by: Sergey Senozhatsky <sergey.senozhatsky@mail.by> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-08-03 11:11:19 -07:00
tty-ldisc: turn ldisc user count into a proper refcount By using the user count for the actual lifetime rules, we can get rid of the silly "wait_for_idle" logic, because any busy ldisc will automatically stay around until the last user releases it. This avoids a host of odd issues, and simplifies the code. So now, when the last ldisc reference is dropped, we just release the ldisc operations struct reference, and free the ldisc. It looks obvious enough, and it does work for me, but the counting _could_ be off. It probably isn't (bad counting in the new version would generally imply that the old code did something really bad, like free an ldisc with a non-zero count), but it does need some testing, and preferably somebody looking at it. With this change, both 'tty_ldisc_put()' and 'tty_ldisc_deref()' are just aliases for the new ref-counting 'put_ldisc()'. Both of them decrement the ldisc user count and free it if it goes down to zero. They're identical functions, in other words. But the reason they still exist as sepate functions is that one of them was exported (tty_ldisc_deref) and had a stupid name (so I don't want to use it as the main name), and the other one was used in multiple places (and I didn't want to make the patch larger just to rename the users). In addition to the refcounting, I did do some minimal cleanup. For example, now "tty_ldisc_try()" actually returns the ldisc it got under the lock, rather than returning true/false and then the caller would look up the ldisc again (now without the protection of the lock). That said, there's tons of dubious use of 'tty->ldisc' without obviously proper locking or refcounting left. I expressly did _not_ want to try to fix it all, keeping the patch minimal. There may or may not be bugs in that kind of code, but they wouldn't be _new_ bugs. That said, even if the bugs aren't new, the timing and lifetime will change. For example, some silly code may depend on the 'tty->ldisc' pointer not changing because they hold a refcount on the 'ldisc'. And that's no longer true - if you hold a ref on the ldisc, the 'ldisc' itself is safe, but tty->ldisc may change. So the proper locking (remains) to hold tty->ldisc_mutex if you expect tty->ldisc to be stable. That's not really a _new_ rule, but it's an example of something that the old code might have unintentionally depended on and hidden bugs. Whatever. The patch _looks_ sensible to me. The only users of ldisc->users are: - get_ldisc() - atomically increment the count - put_ldisc() - atomically decrements the count and releases if zero - tty_ldisc_try_get() - creates the ldisc, and sets the count to 1. The ldisc should then either be released, or be attached to a tty. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Tested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Tested-by: Sergey Senozhatsky <sergey.senozhatsky@mail.by> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-08-03 11:11:19 -07:00
tty-ldisc: turn ldisc user count into a proper refcount By using the user count for the actual lifetime rules, we can get rid of the silly "wait_for_idle" logic, because any busy ldisc will automatically stay around until the last user releases it. This avoids a host of odd issues, and simplifies the code. So now, when the last ldisc reference is dropped, we just release the ldisc operations struct reference, and free the ldisc. It looks obvious enough, and it does work for me, but the counting _could_ be off. It probably isn't (bad counting in the new version would generally imply that the old code did something really bad, like free an ldisc with a non-zero count), but it does need some testing, and preferably somebody looking at it. With this change, both 'tty_ldisc_put()' and 'tty_ldisc_deref()' are just aliases for the new ref-counting 'put_ldisc()'. Both of them decrement the ldisc user count and free it if it goes down to zero. They're identical functions, in other words. But the reason they still exist as sepate functions is that one of them was exported (tty_ldisc_deref) and had a stupid name (so I don't want to use it as the main name), and the other one was used in multiple places (and I didn't want to make the patch larger just to rename the users). In addition to the refcounting, I did do some minimal cleanup. For example, now "tty_ldisc_try()" actually returns the ldisc it got under the lock, rather than returning true/false and then the caller would look up the ldisc again (now without the protection of the lock). That said, there's tons of dubious use of 'tty->ldisc' without obviously proper locking or refcounting left. I expressly did _not_ want to try to fix it all, keeping the patch minimal. There may or may not be bugs in that kind of code, but they wouldn't be _new_ bugs. That said, even if the bugs aren't new, the timing and lifetime will change. For example, some silly code may depend on the 'tty->ldisc' pointer not changing because they hold a refcount on the 'ldisc'. And that's no longer true - if you hold a ref on the ldisc, the 'ldisc' itself is safe, but tty->ldisc may change. So the proper locking (remains) to hold tty->ldisc_mutex if you expect tty->ldisc to be stable. That's not really a _new_ rule, but it's an example of something that the old code might have unintentionally depended on and hidden bugs. Whatever. The patch _looks_ sensible to me. The only users of ldisc->users are: - get_ldisc() - atomically increment the count - put_ldisc() - atomically decrements the count and releases if zero - tty_ldisc_try_get() - creates the ldisc, and sets the count to 1. The ldisc should then either be released, or be attached to a tty. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Tested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Tested-by: Sergey Senozhatsky <sergey.senozhatsky@mail.by> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-08-03 11:11:19 -07:00
tty-ldisc: turn ldisc user count into a proper refcount By using the user count for the actual lifetime rules, we can get rid of the silly "wait_for_idle" logic, because any busy ldisc will automatically stay around until the last user releases it. This avoids a host of odd issues, and simplifies the code. So now, when the last ldisc reference is dropped, we just release the ldisc operations struct reference, and free the ldisc. It looks obvious enough, and it does work for me, but the counting _could_ be off. It probably isn't (bad counting in the new version would generally imply that the old code did something really bad, like free an ldisc with a non-zero count), but it does need some testing, and preferably somebody looking at it. With this change, both 'tty_ldisc_put()' and 'tty_ldisc_deref()' are just aliases for the new ref-counting 'put_ldisc()'. Both of them decrement the ldisc user count and free it if it goes down to zero. They're identical functions, in other words. But the reason they still exist as sepate functions is that one of them was exported (tty_ldisc_deref) and had a stupid name (so I don't want to use it as the main name), and the other one was used in multiple places (and I didn't want to make the patch larger just to rename the users). In addition to the refcounting, I did do some minimal cleanup. For example, now "tty_ldisc_try()" actually returns the ldisc it got under the lock, rather than returning true/false and then the caller would look up the ldisc again (now without the protection of the lock). That said, there's tons of dubious use of 'tty->ldisc' without obviously proper locking or refcounting left. I expressly did _not_ want to try to fix it all, keeping the patch minimal. There may or may not be bugs in that kind of code, but they wouldn't be _new_ bugs. That said, even if the bugs aren't new, the timing and lifetime will change. For example, some silly code may depend on the 'tty->ldisc' pointer not changing because they hold a refcount on the 'ldisc'. And that's no longer true - if you hold a ref on the ldisc, the 'ldisc' itself is safe, but tty->ldisc may change. So the proper locking (remains) to hold tty->ldisc_mutex if you expect tty->ldisc to be stable. That's not really a _new_ rule, but it's an example of something that the old code might have unintentionally depended on and hidden bugs. Whatever. The patch _looks_ sensible to me. The only users of ldisc->users are: - get_ldisc() - atomically increment the count - put_ldisc() - atomically decrements the count and releases if zero - tty_ldisc_try_get() - creates the ldisc, and sets the count to 1. The ldisc should then either be released, or be attached to a tty. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Tested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Tested-by: Sergey Senozhatsky <sergey.senozhatsky@mail.by> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-08-03 11:11:19 -07:00
tty-ldisc: turn ldisc user count into a proper refcount By using the user count for the actual lifetime rules, we can get rid of the silly "wait_for_idle" logic, because any busy ldisc will automatically stay around until the last user releases it. This avoids a host of odd issues, and simplifies the code. So now, when the last ldisc reference is dropped, we just release the ldisc operations struct reference, and free the ldisc. It looks obvious enough, and it does work for me, but the counting _could_ be off. It probably isn't (bad counting in the new version would generally imply that the old code did something really bad, like free an ldisc with a non-zero count), but it does need some testing, and preferably somebody looking at it. With this change, both 'tty_ldisc_put()' and 'tty_ldisc_deref()' are just aliases for the new ref-counting 'put_ldisc()'. Both of them decrement the ldisc user count and free it if it goes down to zero. They're identical functions, in other words. But the reason they still exist as sepate functions is that one of them was exported (tty_ldisc_deref) and had a stupid name (so I don't want to use it as the main name), and the other one was used in multiple places (and I didn't want to make the patch larger just to rename the users). In addition to the refcounting, I did do some minimal cleanup. For example, now "tty_ldisc_try()" actually returns the ldisc it got under the lock, rather than returning true/false and then the caller would look up the ldisc again (now without the protection of the lock). That said, there's tons of dubious use of 'tty->ldisc' without obviously proper locking or refcounting left. I expressly did _not_ want to try to fix it all, keeping the patch minimal. There may or may not be bugs in that kind of code, but they wouldn't be _new_ bugs. That said, even if the bugs aren't new, the timing and lifetime will change. For example, some silly code may depend on the 'tty->ldisc' pointer not changing because they hold a refcount on the 'ldisc'. And that's no longer true - if you hold a ref on the ldisc, the 'ldisc' itself is safe, but tty->ldisc may change. So the proper locking (remains) to hold tty->ldisc_mutex if you expect tty->ldisc to be stable. That's not really a _new_ rule, but it's an example of something that the old code might have unintentionally depended on and hidden bugs. Whatever. The patch _looks_ sensible to me. The only users of ldisc->users are: - get_ldisc() - atomically increment the count - put_ldisc() - atomically decrements the count and releases if zero - tty_ldisc_try_get() - creates the ldisc, and sets the count to 1. The ldisc should then either be released, or be attached to a tty. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Tested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Tested-by: Sergey Senozhatsky <sergey.senozhatsky@mail.by> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-08-03 11:11:19 -07:00
tty-ldisc: turn ldisc user count into a proper refcount By using the user count for the actual lifetime rules, we can get rid of the silly "wait_for_idle" logic, because any busy ldisc will automatically stay around until the last user releases it. This avoids a host of odd issues, and simplifies the code. So now, when the last ldisc reference is dropped, we just release the ldisc operations struct reference, and free the ldisc. It looks obvious enough, and it does work for me, but the counting _could_ be off. It probably isn't (bad counting in the new version would generally imply that the old code did something really bad, like free an ldisc with a non-zero count), but it does need some testing, and preferably somebody looking at it. With this change, both 'tty_ldisc_put()' and 'tty_ldisc_deref()' are just aliases for the new ref-counting 'put_ldisc()'. Both of them decrement the ldisc user count and free it if it goes down to zero. They're identical functions, in other words. But the reason they still exist as sepate functions is that one of them was exported (tty_ldisc_deref) and had a stupid name (so I don't want to use it as the main name), and the other one was used in multiple places (and I didn't want to make the patch larger just to rename the users). In addition to the refcounting, I did do some minimal cleanup. For example, now "tty_ldisc_try()" actually returns the ldisc it got under the lock, rather than returning true/false and then the caller would look up the ldisc again (now without the protection of the lock). That said, there's tons of dubious use of 'tty->ldisc' without obviously proper locking or refcounting left. I expressly did _not_ want to try to fix it all, keeping the patch minimal. There may or may not be bugs in that kind of code, but they wouldn't be _new_ bugs. That said, even if the bugs aren't new, the timing and lifetime will change. For example, some silly code may depend on the 'tty->ldisc' pointer not changing because they hold a refcount on the 'ldisc'. And that's no longer true - if you hold a ref on the ldisc, the 'ldisc' itself is safe, but tty->ldisc may change. So the proper locking (remains) to hold tty->ldisc_mutex if you expect tty->ldisc to be stable. That's not really a _new_ rule, but it's an example of something that the old code might have unintentionally depended on and hidden bugs. Whatever. The patch _looks_ sensible to me. The only users of ldisc->users are: - get_ldisc() - atomically increment the count - put_ldisc() - atomically decrements the count and releases if zero - tty_ldisc_try_get() - creates the ldisc, and sets the count to 1. The ldisc should then either be released, or be attached to a tty. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Tested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Tested-by: Sergey Senozhatsky <sergey.senozhatsky@mail.by> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-08-03 11:11:19 -07:00
tty-ldisc: turn ldisc user count into a proper refcount By using the user count for the actual lifetime rules, we can get rid of the silly "wait_for_idle" logic, because any busy ldisc will automatically stay around until the last user releases it. This avoids a host of odd issues, and simplifies the code. So now, when the last ldisc reference is dropped, we just release the ldisc operations struct reference, and free the ldisc. It looks obvious enough, and it does work for me, but the counting _could_ be off. It probably isn't (bad counting in the new version would generally imply that the old code did something really bad, like free an ldisc with a non-zero count), but it does need some testing, and preferably somebody looking at it. With this change, both 'tty_ldisc_put()' and 'tty_ldisc_deref()' are just aliases for the new ref-counting 'put_ldisc()'. Both of them decrement the ldisc user count and free it if it goes down to zero. They're identical functions, in other words. But the reason they still exist as sepate functions is that one of them was exported (tty_ldisc_deref) and had a stupid name (so I don't want to use it as the main name), and the other one was used in multiple places (and I didn't want to make the patch larger just to rename the users). In addition to the refcounting, I did do some minimal cleanup. For example, now "tty_ldisc_try()" actually returns the ldisc it got under the lock, rather than returning true/false and then the caller would look up the ldisc again (now without the protection of the lock). That said, there's tons of dubious use of 'tty->ldisc' without obviously proper locking or refcounting left. I expressly did _not_ want to try to fix it all, keeping the patch minimal. There may or may not be bugs in that kind of code, but they wouldn't be _new_ bugs. That said, even if the bugs aren't new, the timing and lifetime will change. For example, some silly code may depend on the 'tty->ldisc' pointer not changing because they hold a refcount on the 'ldisc'. And that's no longer true - if you hold a ref on the ldisc, the 'ldisc' itself is safe, but tty->ldisc may change. So the proper locking (remains) to hold tty->ldisc_mutex if you expect tty->ldisc to be stable. That's not really a _new_ rule, but it's an example of something that the old code might have unintentionally depended on and hidden bugs. Whatever. The patch _looks_ sensible to me. The only users of ldisc->users are: - get_ldisc() - atomically increment the count - put_ldisc() - atomically decrements the count and releases if zero - tty_ldisc_try_get() - creates the ldisc, and sets the count to 1. The ldisc should then either be released, or be attached to a tty. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Tested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Tested-by: Sergey Senozhatsky <sergey.senozhatsky@mail.by> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-08-03 11:11:19 -07:00
tty-ldisc: turn ldisc user count into a proper refcount By using the user count for the actual lifetime rules, we can get rid of the silly "wait_for_idle" logic, because any busy ldisc will automatically stay around until the last user releases it. This avoids a host of odd issues, and simplifies the code. So now, when the last ldisc reference is dropped, we just release the ldisc operations struct reference, and free the ldisc. It looks obvious enough, and it does work for me, but the counting _could_ be off. It probably isn't (bad counting in the new version would generally imply that the old code did something really bad, like free an ldisc with a non-zero count), but it does need some testing, and preferably somebody looking at it. With this change, both 'tty_ldisc_put()' and 'tty_ldisc_deref()' are just aliases for the new ref-counting 'put_ldisc()'. Both of them decrement the ldisc user count and free it if it goes down to zero. They're identical functions, in other words. But the reason they still exist as sepate functions is that one of them was exported (tty_ldisc_deref) and had a stupid name (so I don't want to use it as the main name), and the other one was used in multiple places (and I didn't want to make the patch larger just to rename the users). In addition to the refcounting, I did do some minimal cleanup. For example, now "tty_ldisc_try()" actually returns the ldisc it got under the lock, rather than returning true/false and then the caller would look up the ldisc again (now without the protection of the lock). That said, there's tons of dubious use of 'tty->ldisc' without obviously proper locking or refcounting left. I expressly did _not_ want to try to fix it all, keeping the patch minimal. There may or may not be bugs in that kind of code, but they wouldn't be _new_ bugs. That said, even if the bugs aren't new, the timing and lifetime will change. For example, some silly code may depend on the 'tty->ldisc' pointer not changing because they hold a refcount on the 'ldisc'. And that's no longer true - if you hold a ref on the ldisc, the 'ldisc' itself is safe, but tty->ldisc may change. So the proper locking (remains) to hold tty->ldisc_mutex if you expect tty->ldisc to be stable. That's not really a _new_ rule, but it's an example of something that the old code might have unintentionally depended on and hidden bugs. Whatever. The patch _looks_ sensible to me. The only users of ldisc->users are: - get_ldisc() - atomically increment the count - put_ldisc() - atomically decrements the count and releases if zero - tty_ldisc_try_get() - creates the ldisc, and sets the count to 1. The ldisc should then either be released, or be attached to a tty. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Tested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Tested-by: Sergey Senozhatsky <sergey.senozhatsky@mail.by> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-08-03 11:11:19 -07:00
tty: make sure to flush any pending work when halting the ldisc When I rewrote tty ldisc code to use proper reference counts (commits 65b770468e98 and cbe9352fa08f) in order to avoid a race with hangup, the test-program that Eric Biederman used to trigger the original problem seems to have exposed another long-standing bug: the hangup code did the 'tty_ldisc_halt()' to stop any buffer flushing activity, but unlike the other call sites it never actually flushed any pending work. As a result, if you get just the right timing, the pending work may be just about to execute (ie the timer has already triggered and thus cancel_delayed_work() was a no-op), when we then re-initialize the ldisc from under it. That, in turn, results in various random problems, usually seen as a NULL pointer dereference in run_timer_softirq() or a BUG() in worker_thread (but it can be almost anything). Fix it by adding the required 'flush_scheduled_work()' after doing the tty_ldisc_halt() (this also requires us to move the ldisc halt to before taking the ldisc mutex in order to avoid a deadlock with the workqueue executing do_tty_hangup, which requires the mutex). The locking should be cleaned up one day (the requirement to do this outside the ldisc_mutex is very annoying, and weakens the lock), but that's a larger and separate undertaking. Reported-by: Eric W. Biederman <ebiederm@xmission.com> Tested-by: Xiaotian Feng <xtfeng@gmail.com> Tested-by: Yanmin Zhang <yanmin_zhang@linux.intel.com> Tested-by: Dave Young <hidave.darkstar@gmail.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Greg Kroah-Hartman <gregkh@suse.de> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-08-25 09:12:43 -07:00