linux-kernel - Re: Are jump labels broken on 6.11-rc1?

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Message-ID: <20240731001950.GN6352@frogsfrogsfrogs>
Date: Tue, 30 Jul 2024 17:19:50 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Chandan Babu R <chandanbabu@...nel.org>,
	Matthew Wilcox <willy@...radead.org>,
	xfs <linux-xfs@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>, x86@...nel.org,
	tglx@...utronix.de
Subject: Re: Are jump labels broken on 6.11-rc1?

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?

Yes, it does!  After ~8, a full fstests run completes without incident.

(vs. before where it would blow up within 2 minutes)

Thanks for the fix; you can add
Tested-by: Darrick J. Wong <djwong@...nel.org>

--D

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