Re: Are jump labels broken on 6.11-rc1?

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, Jul 30, 2024 at 03:26:26PM +0200, Peter Zijlstra wrote:
> On Tue, Jul 30, 2024 at 01:00:02PM +0530, Chandan Babu R wrote:
> > On Mon, Jul 29, 2024 at 08:38:49 PM -0700, Darrick J. Wong wrote:
> > > Hi everyone,
> > >
> > > I got the following splat on 6.11-rc1 when I tried to QA xfs online
> > > fsck.  Does this ring a bell for anyone?  I'll try bisecting in the
> > > morning to see if I can find the culprit.
> > 
> > xfs/566 on v6.11-rc1 would consistently cause the oops mentioned below.
> > However, I was able to get xfs/566 to successfully execute for five times on a
> > v6.11-rc1 kernel with the following commits reverted,
> > 
> > 83ab38ef0a0b2407d43af9575bb32333fdd74fb2
> > 695ef796467ed228b60f1915995e390aea3d85c6
> > 9bc2ff871f00437ad2f10c1eceff51aaa72b478f
> > 
> > Reinstating commit 83ab38ef0a0b2407d43af9575bb32333fdd74fb2 causes the kernel
> > to oops once again.
> 
> Durr, does this help?
> 
> 
> diff --git a/kernel/jump_label.c b/kernel/jump_label.c
> index 4ad5ed8adf96..57f70dfa1f3d 100644
> --- a/kernel/jump_label.c
> +++ b/kernel/jump_label.c
> @@ -236,7 +236,7 @@ void static_key_disable_cpuslocked(struct static_key *key)
>  	}
>  
>  	jump_label_lock();
> -	if (atomic_cmpxchg(&key->enabled, 1, 0))
> +	if (atomic_cmpxchg(&key->enabled, 1, 0) == 1)

Ah, because key->enabled can be -1 sometimes?  I'll throw that at the
fstests cloud for a few hours and report back.

--D

>  		jump_label_update(key);
>  	jump_label_unlock();
>  }
>