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Biederman" , 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: <87qzjdauv4.ffs@fw13> References: <875x0qclcx.ffs@fw13> <87qzjdauv4.ffs@fw13> Date: Tue, 01 Sep 2026 17:11:45 +0200 Message-ID: <87o6ehatvy.ffs@fw13> MIME-Version: 1.0 Content-Type: text/plain X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 08D711C000B X-Stat-Signature: rtjxizimuebs91yoy6essga3nta9pxt7 X-HE-Tag: 1788275508-265761 X-HE-Meta: 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 BqpfZtdv OFVjR8xs3qfYvApudN5H+Gl+ypL64crPf/ZLHsOYugjA5faTDMFNadmAt1VBiTtvgBrJcON29eoZydI0Le8jGpSPTAN0z2UYlpyvmsxbTy9KQ8wcrQU8V1KPzc0Uaz/wf4tVIVNDEWe7VHOzSYgEGRJngdyjHxAsx73AKU9V4LR2UCSvdAxONZQQjm4rbiuzcqqyvKnH2eSUGXRI2fMhrNYjvnpH1RQ4ut3sqo2zqIbpNti0Rc3y7cWaUV64PYa/5MAOx0uoMPV4Tcs1EBQVPKH5OBIoPMzgPUK3jO0gUtpt1z9mT12J+Q2vhAk5C8JfIoI5T Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Sep 01 2026 at 16:50, Thomas Gleixner wrote: > 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. I'm still thinking that an indicator for a task doing exec(), which is set _before_ de_thread() and removed afterwards would be more sensible than relying on subtle ordering constraints. Along with the nonsense to keep timers queued on a task until release_task(). There is no real benefit from keeping them around at after PF_EXITING is set. Sure someone might argue that the precious CPU cycles consumed in do_exit() afterwards won't be accounted, but seriously? Thanks, tglx