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Date: Wed, 9 Sep 2026 18:00:44 +0200
From: Frederic Weisbecker <frederic@kernel.org>
To: Thomas Gleixner <tglx@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>, stern@rowland.harvard.edu,
	boqun@kernel.org, LKML <linux-kernel@vger.kernel.org>,
	"Cc: Hyunwoo Kim" <imv4bel@gmail.com>,
	Oleg Nesterov <oleg@redhat.com>,
	Christian Brauner <brauner@kernel.org>,
	John Stultz <jstultz@google.com>, Ingo Molnar <mingo@kernel.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	"Eric W. Biederman" <ebiederm@xmission.com>, stable@vger.kernel.org
Subject: Re: [patch V2 1/8] signal: Prevent exec() race
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Le Wed, Sep 09, 2026 at 03:45:36PM +0200, Thomas Gleixner a écrit :
> On Wed, Sep 09 2026 at 14:51, Peter Zijlstra wrote:
> > On Wed, Sep 09, 2026 at 02:45:55PM +0200, Peter Zijlstra wrote:
> >> On Wed, Sep 09, 2026 at 02:13:11PM +0200, Frederic Weisbecker wrote:
> >> > P2(int *next, int *prev, int *pid, spinlock_t *sighand)
> >> > {
> >> > 	int r0;
> >> > 	int r1;
> >> > 	// get target
> >> > 	r0 = READ_ONCE(*pid);
> >> > 	spin_lock(sighand);
> >
> > There is no dependency between r0 and sighand. While I think there is in
> > posixtimer_send_sigqueue(). Does making it smp_load_acquire() help?
> 
> sighand is r0->sighand->siglock and obviously not known before r0 is
> read. So yes there is a data dependency in reality :)

Ah but the script writes *psighand on one hand and the spin_lock on the
other hand does an acquire so of course it works. But that doesn't tell
if that's transferrable through struct pid->task write on one hand and
struct pid->task deref on the other hand plus task->sighand dependencies.

My brain melts enough for today...