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fs: make sure data stored into inode is properly seen before unlocking new inode 

In theory it could happen that on one CPU we initialize a new inode but
clearing of I_NEW | I_LOCK gets reordered before some of the
initialization.  Thus on another CPU we return not fully uptodate inode
from iget_locked().

This seems to fix a corruption issue on ext3 mounted over NFS.

[akpm@linux-foundation.org: add some commentary]
Signed-off-by: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jan Kara 2009-09-21 17:01:06 -07:00 committed by Linus Torvalds
parent 5be461657b
commit 580be0837a
1 changed files with 8 additions and 6 deletions
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14
fs/inode.c
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@ -695,13 +695,15 @@ void unlock_new_inode(struct inode *inode)
}
#endif
/*
* This is special! We do not need the spinlock
* when clearing I_LOCK, because we're guaranteed
* that nobody else tries to do anything about the
* state of the inode when it is locked, as we
* just created it (so there can be no old holders
* that haven't tested I_LOCK).
* This is special! We do not need the spinlock when clearing I_LOCK,
* because we're guaranteed that nobody else tries to do anything about
* the state of the inode when it is locked, as we just created it (so
* there can be no old holders that haven't tested I_LOCK).
* However we must emit the memory barrier so that other CPUs reliably
* see the clearing of I_LOCK after the other inode initialisation has
* completed.
*/
smp_mb();
WARN_ON((inode->i_state & (I_LOCK|I_NEW)) != (I_LOCK|I_NEW));
inode->i_state &= ~(I_LOCK|I_NEW);
wake_up_inode(inode);