VFS: Impose ordering on accesses of d_inode and d_flags

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commit 4bf46a2726 upstream.

Impose ordering on accesses of d_inode and d_flags to avoid the need to do
this:

	if (!dentry->d_inode || d_is_negative(dentry)) {

when this:

	if (d_is_negative(dentry)) {

should suffice.

This check is especially problematic if a dentry can have its type field set
to something other than DENTRY_MISS_TYPE when d_inode is NULL (as in
unionmount).

What we really need to do is stick a write barrier between setting d_inode and
setting d_flags and a read barrier between reading d_flags and reading
d_inode.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
[bwh: Backported to 3.16:
 - Use ACCESS_ONCE() instead of {READ,WRITE}_ONCE()
 - There's no DCACHE_FALLTHRU flag]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

...

This commit is contained in:

David Howells 2015-03-05 14:09:22 +00:00 • committed by Ben Hutchings

parent 7a49bf4347

commit d0058dcb67

2 changed files with 42 additions and 25 deletions

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46

fs/dcache.c

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21

include/linux/dcache.h

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