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

[Jia-Ju Bai]

On 06/05/2017 04:32 PM, Shan Hai wrote:
> On 2017å06æ05æ 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@xxxxxxx>
> > ---
> >   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);
I think you are right. Please ignore my patch.

Thanks,
Jia-Ju Bai