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[209.132.183.28]) by mx.google.com with ESMTPS id e12si1863047qvj.62.2019.03.26.06.30.15 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 26 Mar 2019 06:30:15 -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-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 0CD7383F4C; Tue, 26 Mar 2019 13:30:04 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.68]) by smtp.corp.redhat.com (Postfix) with SMTP id 68DF53843; Tue, 26 Mar 2019 13:29:57 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 26 Mar 2019 14:30:02 +0100 (CET) Date: Tue, 26 Mar 2019 14:29:55 +0100 From: Oleg Nesterov To: Christopher Lameter Cc: Waiman Long , Matthew Wilcox , Andrew Morton , 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: <20190326132955.GA16837@redhat.com> References: <20190321214512.11524-1-longman@redhat.com> <20190321214512.11524-3-longman@redhat.com> <20190322015208.GD19508@bombadil.infradead.org> <20190322111642.GA28876@redhat.com> <01000169a686689d-bc18fecd-95e1-4b3e-8cd5-dad1b1c570cc-000000@email.amazonses.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <01000169a686689d-bc18fecd-95e1-4b3e-8cd5-dad1b1c570cc-000000@email.amazonses.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Tue, 26 Mar 2019 13:30:15 +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: Sorry, I am sick and can't work, hopefully I'll return tomorrow. On 03/22, Christopher Lameter wrote: > > On Fri, 22 Mar 2019, Waiman Long wrote: > > > I am looking forward to it. > > There is also alrady rcu being used in these paths. kfree_rcu() would not > be enough? It is an estalished mechanism that is mature and well > understood. But why do we want to increase the number of rcu callbacks in flight? For the moment, lets discuss the exiting tasks only. The only reason why flush_sigqueue(&tsk->pending) needs spin_lock_irq() is the race with release_posix_timer()->sigqueue_free() from another thread which can remove a SIGQUEUE_PREALLOC'ed sigqueue from list. With the simple patch below flush_sigqueue() can be called lockless with irqs enabled. However, this change is not enough, we need to do something similar with do_sigaction()->flush_sigqueue_mask(), and this is less simple. So I won't really argue with kfree_rcu() but I am not sure this is the best option. Oleg. --- a/kernel/exit.c +++ b/kernel/exit.c @@ -85,6 +85,17 @@ static void __unhash_process(struct task_struct *p, bool group_dead) list_del_rcu(&p->thread_node); } +// Rename me and move into signal.c +void remove_prealloced(struct sigpending *queue) +{ + struct sigqueue *q, *t; + + list_for_each_entry_safe(q, t, &queue->list, list) { + if (q->flags & SIGQUEUE_PREALLOC) + list_del_init(&q->list); + } +} + /* * This function expects the tasklist_lock write-locked. */ @@ -160,16 +171,15 @@ static void __exit_signal(struct task_struct *tsk) * Do this under ->siglock, we can race with another thread * doing sigqueue_free() if we have SIGQUEUE_PREALLOC signals. */ - flush_sigqueue(&tsk->pending); + if (!group_dead) + remove_prealloced(&tsk->pending); tsk->sighand = NULL; spin_unlock(&sighand->siglock); __cleanup_sighand(sighand); clear_tsk_thread_flag(tsk, TIF_SIGPENDING); - if (group_dead) { - flush_sigqueue(&sig->shared_pending); + if (group_dead) tty_kref_put(tty); - } } static void delayed_put_task_struct(struct rcu_head *rhp) @@ -221,6 +231,11 @@ void release_task(struct task_struct *p) write_unlock_irq(&tasklist_lock); cgroup_release(p); release_thread(p); + + flush_sigqueue(&p->pending); + if (thread_group_leader(p)) + flush_sigqueue(&p->signal->shared_pending); + call_rcu(&p->rcu, delayed_put_task_struct); p = leader;