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[84.3.50.134]) by smtp.gmail.com with ESMTPSA id n1sm2201159wrw.52.2019.12.09.23.21.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 09 Dec 2019 23:21:21 -0800 (PST) Date: Tue, 10 Dec 2019 08:21:19 +0100 From: Ingo Molnar To: Oleg Nesterov Cc: Linus Torvalds , Peter Zijlstra , Juri Lelli , Vincent Guittot , Miklos Szeredi , Linux Kernel Mailing List , Felipe Balbi Subject: Re: [RFC PATCH] sched/wait: Make interruptible exclusive waitqueue wakeups reliable Message-ID: <20191210072119.GA114501@gmail.com> References: <20191209091813.GA41320@gmail.com> <20191209102759.GA123769@gmail.com> <20191209130005.GB5388@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191209130005.GB5388@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Oleg Nesterov wrote: > On 12/09, Ingo Molnar wrote: > > > > Any consumed exclusive event is handled in finish_wait_exclusive() now: > > > > + } else { > > + /* We got removed from the waitqueue already, wake up the next exclusive waiter (if any): */ > > + if (interrupted && waitqueue_active(wq_head)) > > + __wake_up_locked_key(wq_head, TASK_NORMAL, NULL); > > See my previous email, I don't think we need this... > > But if we do this, then __wake_up_locked_key(key => NULL) doesn't look right. > It should use the same "key" which was passed to __wake_up(key) which removed > us from list. > > Currently this doesn't really matter, the only user of prepare_to_wait_event() > which relies on the "keyed" wakeup is ___wait_var_event() and it doesn't have > "exclusive" waiters, but still. > > Hmm. and it seems that init_wait_var_entry() is buggy? Again, currently this > doesn't matter, but don't we need the trivial fix below? > > Oleg. > > --- x/kernel/sched/wait_bit.c > +++ x/kernel/sched/wait_bit.c > @@ -179,6 +179,7 @@ void init_wait_var_entry(struct wait_bit > .bit_nr = -1, > }, > .wq_entry = { > + .flags = flags, > .private = current, > .func = var_wake_function, > .entry = LIST_HEAD_INIT(wbq_entry->wq_entry.entry), Yeah, agreed. Thanks, Ingo