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[198.145.29.96]) by mx.google.com with ESMTPS id i96si1324225pje.4.2019.06.10.21.39.12 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 10 Jun 2019 21:39:12 -0700 (PDT) Received-SPF: pass (google.com: domain of gkohli@codeaurora.org designates 198.145.29.96 as permitted sender) client-ip=198.145.29.96; Authentication-Results: mx.google.com; dkim=pass header.i=@codeaurora.org header.s=default header.b=dob0nTtT; dkim=pass header.i=@codeaurora.org header.s=default header.b=fC1I4+x5; spf=pass (google.com: domain of gkohli@codeaurora.org designates 198.145.29.96 as permitted sender) smtp.mailfrom=gkohli@codeaurora.org Received: by smtp.codeaurora.org (Postfix, from userid 1000) id 4CE95604BE; Tue, 11 Jun 2019 04:39:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1560227952; bh=GxvWGt9BSFpOm0HBYOLwuO1UUTw67j40yC2FZPp7lcY=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=dob0nTtTztsKrzbG99s2RNDLafJK+yaBUpEXQ50HfnN1Smzg9myH8GKQJ2MZoaVQj G5hQwVyQ6pj1OUJIYTClnu/jnu1+MXJy5foM5B8pC2yesIggzo9qY84y4cXZ7tRIsa ONChedqqzDeYrgyxUVbFO/uyAAU4Trs/UqGlaTNo= Received: from [10.204.79.142] (blr-c-bdr-fw-01_globalnat_allzones-outside.qualcomm.com [103.229.19.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: gkohli@smtp.codeaurora.org) by smtp.codeaurora.org (Postfix) with ESMTPSA id 3DE0460261; Tue, 11 Jun 2019 04:39:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1560227951; bh=GxvWGt9BSFpOm0HBYOLwuO1UUTw67j40yC2FZPp7lcY=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=fC1I4+x5OBGfNCBsYpH8gEdI1mu+JvSeL2VIuUVgwIHFBfoBqyhXRLlk8Ynaruyiv DVZbPNoB5Po6eIKDJG9vrTPtDHHB2v3kvXeJz5kR44kDeTFJIQg0b1HiIkPfmageka zvesMBiGovazHRLrl/FJLMoQiHGOnNA9IEj0zBLg= DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 3DE0460261 Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=gkohli@codeaurora.org Subject: Re: [PATCH] block: fix a crash in do_task_dead() To: Oleg Nesterov Cc: Peter Zijlstra , Jens Axboe , Qian Cai , akpm@linux-foundation.org, hch@lst.de, mingo@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1559161526-618-1-git-send-email-cai@lca.pw> <20190530080358.GG2623@hirez.programming.kicks-ass.net> <82e88482-1b53-9423-baad-484312957e48@kernel.dk> <20190603123705.GB3419@hirez.programming.kicks-ass.net> <20190607133541.GJ3436@hirez.programming.kicks-ass.net> <20190607142332.GF3463@hirez.programming.kicks-ass.net> <16419960-3703-5988-e7ea-9d3a439f8b05@codeaurora.org> <20190610144641.GA8127@redhat.com> From: Gaurav Kohli Message-ID: <154008a8-9d29-2411-28a0-0284a95b4481@codeaurora.org> Date: Tue, 11 Jun 2019 10:09:06 +0530 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190610144641.GA8127@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit 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: >>> + >> >> Hi Peter, Jen, >> >> As we are not taking pi_lock here , is there possibility of same task dead >> call comes as this point of time for current thread, bcoz of which we have >> seen earlier issue after this commit 0619317ff8ba >> [T114538] do_task_dead+0xf0/0xf8 >> [T114538] do_exit+0xd5c/0x10fc >> [T114538] do_group_exit+0xf4/0x110 >> [T114538] get_signal+0x280/0xdd8 >> [T114538] do_notify_resume+0x720/0x968 >> [T114538] work_pending+0x8/0x10 >> >> Is there a chance of TASK_DEAD set at this point of time? > > In this case try_to_wake_up(current, TASK_NORMAL) will do nothing, see the > if (!(p->state & state)) above. > > See also the comment about set_special_state() above. It disables irqs and > this is enough to ensure that try_to_wake_up(current) from irq can't race > with set_special_state(TASK_DEAD). Thanks Oleg, I missed that part(both thread and interrupt is in same core only), So that situation would never come. > > Oleg. > -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.