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Wed, 11 Nov 2026 23:01:40 +0000 (UTC) Received: from onestero-thinkpadp1gen7.tpbc.csb (headnet04.pony-001.prod.iad2.dc.redhat.com [10.2.32.116]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id 01DC41800495; Wed, 11 Nov 2026 23:01:36 +0000 (UTC) Received: by onestero-thinkpadp1gen7.tpbc.csb (nbSMTP-1.00) for uid 13628 oleg@redhat.com; Thu, 12 Nov 2026 00:01:39 +0100 (CET) Date: Thu, 12 Nov 2026 00:01:35 +0100 From: Oleg Nesterov To: Mani Tofigh via B4 Relay Cc: Peter Zijlstra , Ingo Molnar , Christian Brauner , Michal Nazarewicz , Wen Yang , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, tz2294@columbia.edu, stable@vger.kernel.org, Mani Tofigh Subject: Re: [PATCH] sched/wait: Queue non-exclusive waiters at the head in do_wait_intr*() Message-ID: References: <20261111-b4-sched-wait-intr-head-v1-1-17cf2af5b964@columbia.edu> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261111-b4-sched-wait-intr-head-v1-1-17cf2af5b964@columbia.edu> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 On 11/11, Mani Tofigh via B4 Relay wrote: > > --- a/kernel/sched/wait.c > +++ b/kernel/sched/wait.c > @@ -319,8 +319,12 @@ EXPORT_SYMBOL(prepare_to_wait_event); > */ > int do_wait_intr(wait_queue_head_t *wq, wait_queue_entry_t *wait) > { > - if (likely(list_empty(&wait->entry))) > - __add_wait_queue_entry_tail(wq, wait); > + if (likely(list_empty(&wait->entry))) { > + if (wait->flags & WQ_FLAG_EXCLUSIVE) > + __add_wait_queue_entry_tail(wq, wait); > + else > + __add_wait_queue(wq, wait); This look right and matches prepare_to_wait_event(). But it seems there is another problem if WQ_FLAG_EXCLUSIVE, see the "Exclusive waiter must not fail if it was selected by wakeup" comment in prepare_to_wait_event(). Perhaps it makes more sense to simply kill __wait_event_interruptible_locked() and reimplement wait_event_interruptible_locked() on top of ___wait_event(cmd => do_wait_intr) ? This way do_wait_intr() will only need to do unlock + schedule + lock. Oleg.