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SubjectRe: [PATCH] fs: xfs: Fix a lock-twice and sleep-in-atomic bug in xfs_iget
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On 2017年06月05日 16:17, Jia-Ju Bai wrote:
> 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@163.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();

Seems you are going to double unlock by doing this, since it is unlocked
in the xfs_iget_cache_hit.

Thanks
Shan Hai

> goto out_error_or_again;
> + }
> } else {
> rcu_read_unlock();
> XFS_STATS_INC(mp, xs_ig_missed);

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