fs: dcache: Use READ_ONCE when accessing i_dir_seq

i_dir_seq is subject to concurrent modification by a cmpxchg or
store-release operation, so ensure that the relaxed access in
d_alloc_parallel uses READ_ONCE.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/dcache.c b/fs/dcache.c
index bde3b66..8945e6c 100644 (file)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2507,7 +2507,7 @@ retry:
        }
 
        hlist_bl_lock(b);
-       if (unlikely(parent->d_inode->i_dir_seq != seq)) {
+       if (unlikely(READ_ONCE(parent->d_inode->i_dir_seq) != seq)) {
                hlist_bl_unlock(b);
                rcu_read_unlock();
                goto retry;