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[209.132.183.28]) by mx.google.com with ESMTPS id p67si4618041qkd.272.2019.03.22.04.16.51 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 22 Mar 2019 04:16:51 -0700 (PDT) Received-SPF: pass (google.com: domain of oleg@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of oleg@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=oleg@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id BEC5B3083363; Fri, 22 Mar 2019 11:16:50 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.32]) by smtp.corp.redhat.com (Postfix) with SMTP id 41AA71A914; Fri, 22 Mar 2019 11:16:45 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Fri, 22 Mar 2019 12:16:48 +0100 (CET) Date: Fri, 22 Mar 2019 12:16:42 +0100 From: Oleg Nesterov To: Matthew Wilcox Cc: Waiman Long , Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , linux-kernel@vger.kernel.org, linux-mm@kvack.org, selinux@vger.kernel.org, Paul Moore , Stephen Smalley , Eric Paris , "Peter Zijlstra (Intel)" Subject: Re: [PATCH 2/4] signal: Make flush_sigqueue() use free_q to release memory Message-ID: <20190322111642.GA28876@redhat.com> References: <20190321214512.11524-1-longman@redhat.com> <20190321214512.11524-3-longman@redhat.com> <20190322015208.GD19508@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190322015208.GD19508@bombadil.infradead.org> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Fri, 22 Mar 2019 11:16:51 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 03/21, Matthew Wilcox wrote: > > On Thu, Mar 21, 2019 at 05:45:10PM -0400, Waiman Long wrote: > > > To avoid this dire condition and reduce lock hold time of tasklist_lock, > > flush_sigqueue() is modified to pass in a freeing queue pointer so that > > the actual freeing of memory objects can be deferred until after the > > tasklist_lock is released and irq re-enabled. > > I think this is a really bad solution. It looks kind of generic, > but isn't. It's terribly inefficient, and all it's really doing is > deferring the debugging code until we've re-enabled interrupts. Agreed. > We'd be much better off just having a list_head in the caller > and list_splice() the queue->list onto that caller. Then call > __sigqueue_free() for each signal on the queue. This won't work, note the comment which explains the race with sigqueue_free(). Let me think about it... at least we can do something like close_the_race_with_sigqueue_free(struct sigpending *queue) { struct sigqueue *q, *t; list_for_each_entry_safe(q, t, ...) { if (q->flags & SIGQUEUE_PREALLOC) list_del_init(&q->list); } called with ->siglock held, tasklist_lock is not needed. After that flush_sigqueue() can be called lockless in release_task() release_task. I'll try to make the patch tomorrow. Oleg.