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>
diff --git a/fs/inode.c b/fs/inode.c
index b2ba83d..798052f 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -695,13 +695,15 @@
}
#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);
