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From: Thomas Gleixner <tglx@kernel.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Hyunwoo Kim <imv4bel@gmail.com>, Frederic Weisbecker
 <frederic@kernel.org>, Anna-Maria Behnsen <anna-maria@linutronix.de>, Kees
 Cook <kees@kernel.org>, Christian Brauner <brauner@kernel.org>, Peter
 Zijlstra <peterz@infradead.org>, John Stultz <jstultz@google.com>, Ingo
 Molnar <mingo@kernel.org>, Alexander Viro <viro@zeniv.linux.org.uk>, Jan
 Kara <jack@suse.cz>, "Eric W. Biederman" <ebiederm@xmission.com>,
 linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
 linux-mm@kvack.org
Subject: Re: [PATCH v2] posix-cpu-timers: Dequeue per-thread timers before
 exchange_tids()
In-Reply-To: <apXGzcA9BmrbrQZv@redhat.com>
References: <ao7Q8miiuLAPVnWv@v4bel> <ao7iQ_wOLghOvTsq@redhat.com>
 <875x0qclcx.ffs@fw13> <apXGzcA9BmrbrQZv@redhat.com>
Date: Tue, 01 Sep 2026 16:50:39 +0200
Message-ID: <87qzjdauv4.ffs@fw13>
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On Mon, Aug 31 2026 at 20:24, Oleg Nesterov wrote:
> On 08/31, Thomas Gleixner wrote:
>>
>> On Wed, Aug 26 2026 at 14:55, Oleg Nesterov wrote:
>> > Can we move posix_cpu_timers_exit() or the whole CONFIG_POSIX_TIMERS
>> > sequence in begin_new_exec() up, right after de_thread() before the
>> > "if (retval)" check?
>>
>> Yes, but that does not buy us anything.
>
> I didn't mean this makes sense, I just tried to understand the Hyunwoo's
> fix, in particular the placement of additional posix_cpu_timers_exit().

Fair enough. But as I was staring at it some more, I thought more about
it. Yes, we can do:

     ret = de_thread()
     if (ret)
     	goto out;

     mop_up_posix_timers();

de_thread() only returns failure _before_ the TID swap, so that's safe
and spares sprinkling this extra invocation into de_thread().

What a mess.