fs: fix superblock iteration race
list_for_each_entry_safe is not suitable to protect against concurrent
modification of the list. 6754af6 introduced a race in sb walking.
list_for_each_entry can use the trick of pinning the current entry in
the list before we drop and retake the lock because it subsequently
follows cur->next. However list_for_each_entry_safe saves n=cur->next
for following before entering the loop body, so when the lock is
dropped, n may be deleted.
Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: John Stultz <johnstul@us.ibm.com>
Cc: Frank Mayhar <fmayhar@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/dcache.c b/fs/dcache.c
index d96047b..c8c78ba 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -590,6 +590,8 @@
up_read(&sb->s_umount);
}
spin_lock(&sb_lock);
+ /* lock was dropped, must reset next */
+ list_safe_reset_next(sb, n, s_list);
count -= pruned;
__put_super(sb);
/* more work left to do? */