linux-kernel - Re: fs: WARNING in locks_unlink_lock

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Date:   Sat, 08 Oct 2016 06:47:21 -0400
From:   Jeff Layton <jlayton@...chiereds.net>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Bruce Fields <bfields@...ldses.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: fs: WARNING in locks_unlink_lock_ctx (not holding proper lock)

On Sat, 2016-10-08 at 10:12 +0200, Peter Zijlstra wrote:
> On Fri, Oct 07, 2016 at 07:26:36PM -0400, Jeff Layton wrote:
> 
> > 
> > Well spotted. Yeah, I think you're right. The assertion is this:
> > 
> >     percpu_rwsem_assert_held(&file_rwsem);
> > 
> > I'm guessing this is probably fallout from the lglock to rwsem
> > conversion (commit aba376607383).
> > 
> > From a quick glance, I think we probably just need to down_read the
> > file_rwsem in locks_remove_lease, prior to taking the flc_lock, and
> > release it just afterward.
> 
> Correct on all that.
> 
> > 
> > I do want to go over the code a little more
> > closely though to make sure other codepaths aren't missing that lock
> > though.
> 
> Urg, sorry for missing these, I went through it again and found the
> below to be missing.
> 
> ---
> Subject: fs/locks: Add missing file_sem locks
> 
> I overlooked a few code-paths that can lead to
> locks_delete_global_locks().
> 
> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
> 
> diff --git a/fs/locks.c b/fs/locks.c
> index 133fb2543d21..c623490863a9 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -1604,6 +1604,7 @@ int fcntl_getlease(struct file *filp)
>  
>  	ctx = smp_load_acquire(&inode->i_flctx);
>  	if (ctx && !list_empty_careful(&ctx->flc_lease)) {
> +		percpu_down_read_preempt_disable(&file_rwsem);
>  		spin_lock(&ctx->flc_lock);
>  		time_out_leases(file_inode(filp), &dispose);
>  		list_for_each_entry(fl, &ctx->flc_lease, fl_list) {
> @@ -1613,6 +1614,8 @@ int fcntl_getlease(struct file *filp)
>  			break;
>  		}
>  		spin_unlock(&ctx->flc_lock);
> +		percpu_up_read_preempt_enable(&file_rwsem);
> +
>  		locks_dispose_list(&dispose);
>  	}
>  	return type;
> @@ -2522,11 +2525,14 @@ locks_remove_lease(struct file *filp, struct file_lock_context *ctx)
>  	if (list_empty(&ctx->flc_lease))
>  		return;
>  
> +	percpu_down_read_preempt_disable(&file_rwsem);
>  	spin_lock(&ctx->flc_lock);
>  	list_for_each_entry_safe(fl, tmp, &ctx->flc_lease, fl_list)
>  		if (filp == fl->fl_file)
>  			lease_modify(fl, F_UNLCK, &dispose);
>  	spin_unlock(&ctx->flc_lock);
> +	percpu_up_read_preempt_enable(&file_rwsem);
> +
>  	locks_dispose_list(&dispose);
>  }
>  

Looks correct to me.

Peter, do you need me to pick this patch up or do you plan to get it to
Linus another way?

Thanks, and:

Reviewed-by: Jeff Layton <jlayton@...chiereds.net>