linux-kernel - [PATCH] fs: xfs: Fix a lock-twice and sleep-in-atomic bug in xfs

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Date:   Mon,  5 Jun 2017 16:17:29 +0800
From:   Jia-Ju Bai <baijiaju1990@....com>
To:     darrick.wong@...cle.com
Cc:     linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jia-Ju Bai <baijiaju1990@....com>
Subject: [PATCH] fs: xfs: Fix a lock-twice and sleep-in-atomic bug in xfs_iget

The driver may sleep under a read rcu lock, and function call path is:
xfs_iget (acquire the lock by rcu_read_lock)
  "goto out_error_or_again" after xfs_iget_cache_hit
    delay
      schedule_timeout_uninterruptible --> may sleep
Meanwhile, the rcu_read_lock will be called twice in this situation.

To fix it, the lock is released before "goto".

Signed-off-by: Jia-Ju Bai <baijiaju1990@....com>
---
 fs/xfs/xfs_icache.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
index f61c84f8..c2a4722 100644
--- a/fs/xfs/xfs_icache.c
+++ b/fs/xfs/xfs_icache.c
@@ -600,8 +600,10 @@ struct xfs_inode *
 
 	if (ip) {
 		error = xfs_iget_cache_hit(pag, ip, ino, flags, lock_flags);
-		if (error)
+		if (error) {
+			rcu_read_unlock();
 			goto out_error_or_again;
+		}
 	} else {
 		rcu_read_unlock();
 		XFS_STATS_INC(mp, xs_ig_missed);
-- 
1.7.9.5