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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Frederic Weisbecker <frederic@kernel.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Anna-Maria Behnsen <anna-maria@linutronix.de>,
        John Stultz <jstultz@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Stephen Boyd <sboyd@kernel.org>,
        Eric Biederman <ebiederm@xmission.com>,
        Oleg Nesterov <oleg@redhat.com>
Subject: Re: [patch 14/45] posix-timers: Consolidate interval retrieval
In-Reply-To: <ZJ7g1NvmxnKqCLC9@lothringen>
References: <20230606132949.068951363@linutronix.de>
 <20230606142031.816970056@linutronix.de>
 <ZJww66Svi84Bvw9Z@localhost.localdomain> <87ttuq14xp.ffs@tglx>
 <ZJ67nQ6Q8F3mu6Jb@lothringen> <875y75yu7u.ffs@tglx>
 <ZJ7g1NvmxnKqCLC9@lothringen>
Date:   Sat, 01 Jul 2023 20:01:01 +0200
Message-ID: <87bkgvy0iq.ffs@tglx>
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On Fri, Jun 30 2023 at 16:04, Frederic Weisbecker wrote:
> On Fri, Jun 30, 2023 at 03:07:17PM +0200, Thomas Gleixner wrote:
>> How exactly does this end up being copied to user space if ret != 0?
>
> kc->timer_get() doesn't return any value.
>
> So before the patch, interval is retrieved only if the target is not reaped:
>
> timer_gettime() {
>     do_timer_gettime() {
>         posix_cpu_timer_get() {
>             p = cpu_timer_task_rcu(timer);
>             if (p)
>                 itp->interval = ....
>         }
>     }
> }
>
> After the patch it's retrieved unconditionally:
>
> timer_gettime() {
>     do_timer_gettime() {
>         //unconditionally set
>         itp->interval = ....
>         posix_cpu_timer_get() {
>             p = cpu_timer_task_rcu(timer);
>             if (!p)
>                 //doesn't return any value so no failure reported

Duh. you are right ...