linux-kernel - Re: [PATCH] posix-timers: Handle returned errors poperly in [i]timer

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Date: Mon, 15 Apr 2024 18:27:58 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Anna-Maria Behnsen <anna-maria@...utronix.de>
Cc: Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	John Stultz <jstultz@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, Stephen Boyd <sboyd@...nel.org>,
	Eric Biederman <ebiederm@...ssion.com>
Subject: Re: [PATCH] posix-timers: Handle returned errors poperly in
 [i]timer_delete()

Anna-Maria, I can't really answer, I don't understand this code today ;)
That said, let me try to explain my opinion,

On 04/15, Anna-Maria Behnsen wrote:
>
> Oleg Nesterov <oleg@...hat.com> writes:
>
> > On 04/15, Anna-Maria Behnsen wrote:
> >>
> >> timer_delete_hook() returns -EINVAL when the clock or the timer_del
> >> callback of the clock does not exist. This return value is not handled by
> >> the callsites timer_delete() and itimer_delete().
> >
> > IIUC this shouldn't happen? timer_delete_hook() WARN()s in this case,
> > not sure we need to return this error to userspace...
>
> This shouldn't happen, right.
>
> Even if we do not return this error to userspace, is it valid to proceed
> with the rest of the callsites?

Well, I'd say that nothing is safe after we hit the kernel problem.

But lets suppose we return EINVAL and skip list_del(&timer->list)/etc.
How can this help? What can userspace do to resolve this problem? Is it
better to "leak" this timer? I dunno.

> When it is fine to just ignore the
> -EINVAL return, then I would propose just to add a comment to the code.

Agreed!

Oleg.