btrfs: fix readdir deadlock with pagefault

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Readdir does dir_emit while under the btree lock.  dir_emit can trigger
the page fault which means we can deadlock.  Fix this by allocating a
buffer on opening a directory and copying the readdir into this buffer
and doing dir_emit from outside of the tree lock.

Thread A
readdir  <holding tree lock>
  dir_emit
    <page fault>
      down_read(mmap_sem)

Thread B
mmap write
  down_write(mmap_sem)
    page_mkwrite
      wait_ordered_extents

Process C
finish_ordered_extent
  insert_reserved_file_extent
   try to lock leaf <hang>

Signed-off-by: Josef Bacik <jbacik@fb.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ copy the deadlock scenario to changelog ]
Signed-off-by: David Sterba <dsterba@suse.com>

...

This commit is contained in:

Josef Bacik 2017-07-24 15:14:25 -04:00 • committed by David Sterba

parent 8d8aafeea2

commit 23b5ec7494

4 changed files with 110 additions and 34 deletions

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5

fs/btrfs/ctree.h

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9

fs/btrfs/file.c

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108

fs/btrfs/inode.c

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22

fs/btrfs/ioctl.c

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