From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 028F1FB44C6 for ; Fri, 24 Apr 2026 07:38:40 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3A03D6B008A; Fri, 24 Apr 2026 03:38:40 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 378A76B008C; Fri, 24 Apr 2026 03:38:40 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 28E366B0092; Fri, 24 Apr 2026 03:38:40 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 150776B008A for ; Fri, 24 Apr 2026 03:38:40 -0400 (EDT) Received: from smtpin12.hostedemail.com (lb01b-stub [10.200.18.250]) by unirelay10.hostedemail.com (Postfix) with ESMTP id C2B9BC244D for ; Fri, 24 Apr 2026 07:38:39 +0000 (UTC) X-FDA: 84692647158.12.E1A18FE Received: from mail-wm1-f44.google.com (mail-wm1-f44.google.com [209.85.128.44]) by imf17.hostedemail.com (Postfix) with ESMTP id B7D5F40007 for ; Fri, 24 Apr 2026 07:38:37 +0000 (UTC) Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=suse.com header.s=google header.b=P5AWZQ4m; spf=pass (imf17.hostedemail.com: domain of mhocko@suse.com designates 209.85.128.44 as permitted sender) smtp.mailfrom=mhocko@suse.com; dmarc=pass (policy=quarantine) header.from=suse.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1777016318; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=7sRCoE676JeZHeB3B8L45JxboYFG9w4g6sbDNRxrI1Y=; b=Fp0gShyncNyqkQl+y8lJbjuPgrEFjC5NenOtQnaHTFk71wuPA6ahBLAeOwhH2UHqoGPaZR hw/p5IVzQOcy+yjTqiaZQJceYVAbcIeB9m/mdVTMAZIXpNS/ZXcfPL2OmN88Z2DP/WZBwb PJ6CIi8z6AAM+7ty4e77fHjKw3J4FCY= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1777016318; a=rsa-sha256; cv=none; b=0K7IQW6rHpwiU697MBmqFJ3tQMyIkhki/xC94xwu0VoWlJ7ZXTWZqUTN7aWcM9Lsva/xTs YIDctyAi9Rq5qv/3TWQ343jKK8uIMHl1kAUH6XHVj4guVlZAsAT2DbobfdcX8Tp8GVmWuu yR2DLsvGDMmqnIz9C2fYdWqegCMg0nc= ARC-Authentication-Results: i=1; imf17.hostedemail.com; dkim=pass header.d=suse.com header.s=google header.b=P5AWZQ4m; spf=pass (imf17.hostedemail.com: domain of mhocko@suse.com designates 209.85.128.44 as permitted sender) smtp.mailfrom=mhocko@suse.com; dmarc=pass (policy=quarantine) header.from=suse.com Received: by mail-wm1-f44.google.com with SMTP id 5b1f17b1804b1-4891e5b9c1fso56108015e9.2 for ; Fri, 24 Apr 2026 00:38:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=google; t=1777016316; x=1777621116; darn=kvack.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=7sRCoE676JeZHeB3B8L45JxboYFG9w4g6sbDNRxrI1Y=; b=P5AWZQ4m7TLJfaTDfzmwiuYJ1RzPYi9Sve5p4crcngVTh7qNqdFUnTtA6D21DvOSgU sE222oXRUVLSVf2MXgR+6QxDxbdPyN8Pp8/d+mcml4YeKlhamVb5RN9b/SE6JQw9hNDj M9n3V3CpHNzITZQJa5dD/LQl8w3Vs8uhoMcaq1tnBEbUCAiUTsnh2ABmLIZDcRfIxXmF Aq8HXsw4KEYTwo73nRePY8xXpPuZyrT1TrvFJh9/j53ncTnKUH1rAFilI1JPCQqTouEA JA/b9gW9H2wLG+tDE++lsRzka/4QWIQIsaROThWXGdrRiIranlNXx5clGWMz+3xis7dU 6gaw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1777016316; x=1777621116; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=7sRCoE676JeZHeB3B8L45JxboYFG9w4g6sbDNRxrI1Y=; b=muKbydXC/Yyl8+TAcI5Kum54BG3fSOQ2g8GuOoE8e+ARNnPi0r65m3v0dlm/n0f2Ab AaEFaHUqxSxE83hbVIvZ1J9TAcr5hnB0alNloUqy0ttLyPwdwHju1HbNgzU4SbbiSrrD 7d6cPPjlo3t/9K+bvzv4AdNnqJ6AoPAQ3vnuVwQwMdhkYSlphwmSX92F+WeOGHHFXYPZ pP3bQBmfeHniNoAqaepX8KrNT1FMhkvxMoIs6i+Bp06V4AmvePgcOWyPK4D8tcA0AM0X I3ZVWYHpzV4bHgbrFPYjZ4WAs5EjQo42SXmRtBFsz57mqkRWnWRGNMzOjrZdoK7dS39n gvvw== X-Forwarded-Encrypted: i=1; AFNElJ+53cBkbDzCITDzhgpJnJFj6K+rlR+xAQmuTYZZqze+aMS6Wl064oXWBx4PeLmT579r1qntXrcC5Q==@kvack.org X-Gm-Message-State: AOJu0Yw9WfnfXhwnYl9yIYA5DXs7c4PDN70xUxCzIZ5yk9/7Oxb8kubd P8Uki9mLRxj5o08EjzlzAKa/d9uz4Kjbyv0slGHizHVW4H3NKjk6219ZV0BAf/z4L5E= X-Gm-Gg: AeBDiesfo4DIctnGJIgUACaC6VRZCcED5Gc2bPCk0HUtOqtJ6XEMv69dCj0DQmMMfKR 6TybmhZYmSzrLX3AFEk7VutkS1i6FbeNZdWz+C6L9NF6liLLgOaVaiXBiSK66lOBt0rFpjg2dmy ugf1y/xVfdru7yfXApR33HS9CvyMvMxqRAHMlMB44bnjDbJuuLtFoY4ri6wH4khIzCoSD5enQe7 87dy42TpwR6KQJFMI5KiAF+JoCUNf9KId6mH/BSVoredphtHNhR0AxsQg9Mzs6DNXDmWznYjvDM 7rO+yx7zHngCm8sFWWa6YEqX7EL0V25mTFg6B2iREIS/kCZH0ZQdwuDpLecNRzHLu4B6eJOd6DB nEzNqfRh9V1+MHNBYjWZKzBvZr7XBnlvh0OtLdzCfFyq7/T1/ozswcjME+L7UTDA+kZhjZFhmJw WB+rM+u8zfb/U0YIYlV1sGfm16B7LJe4SJ9PfIKEPmmw+cvYU= X-Received: by 2002:a05:600c:6206:b0:48a:599a:3716 with SMTP id 5b1f17b1804b1-48a599a3bfamr155991265e9.23.1777016315877; Fri, 24 Apr 2026 00:38:35 -0700 (PDT) Received: from localhost (109-81-17-171.rct.o2.cz. [109.81.17.171]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-488fc0f82bbsm979447725e9.3.2026.04.24.00.38.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 24 Apr 2026 00:38:35 -0700 (PDT) Date: Fri, 24 Apr 2026 09:38:34 +0200 From: Michal Hocko To: Minchan Kim Cc: Christian Brauner , akpm@linux-foundation.org, david@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, surenb@google.com, timmurray@google.com Subject: Re: [RFC 3/3] mm: process_mrelease: introduce PROCESS_MRELEASE_REAP_KILL flag Message-ID: References: <20260413223948.556351-1-minchan@kernel.org> <20260413223948.556351-4-minchan@kernel.org> <20260416-planktont-abwinken-b9499483b939@brauner> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: wsfcapyf1co4bsur3ugxxdgsbksbe5ep X-Rspam-User: X-Rspamd-Queue-Id: B7D5F40007 X-Rspamd-Server: rspam05 X-HE-Tag: 1777016317-355910 X-HE-Meta: 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 OR1dCbiQ 7gL1EmQjSWsV0qHnmpg0yzkni9CODEvz3fyrA137ONgrKH/7Mdx5OvvCOwz4fYgGOTgoKKjvtpQE2dyc8GZnFqW0W/US398CyQWBtzARgN0+dTFLIJRWlPNrmSmNgXScRsChLZOrfDbiaVWMP1qcQ43nKVrYYsfNzCtlJ/rAxcB3War1TMoLx3GD4R/9Mik7FsJlmu492S3rGYboNlK8fyShDVwIgsim4o6iWrC3+D9vXsPQQ/hOQhnCjaU9neswu9WMzkv1Uj7YGMM5zzBtaAQPD+VUU0d2xPLIN3zu/JRKFNjPnv5+slTVcEUek06PUz7aJj/MhJvNcdoPD5iKhF1y87GPclhTMfFRkokgn+4grd518HoqgVbtIlaTSvT5kcU3jLqWh5WWzC2mMqkbXayMEERqWB4adBVAnwOLXQMq1iKs= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu 23-04-26 16:43:48, Minchan Kim wrote: > On Thu, Apr 23, 2026 at 09:17:39AM +0200, Michal Hocko wrote: > > On Mon 20-04-26 14:47:04, Minchan Kim wrote: > > > On Fri, Apr 17, 2026 at 09:04:31AM +0200, Michal Hocko wrote: > > > > On Thu 16-04-26 23:30:09, Minchan Kim wrote: > > > > > If I send the SIGKILL first to satisfy the process_mrelease() requirement, > > > > > we immediately run into the scheduling race condition where the victim can > > > > > enter the exit path before the reaper can set the flag. > > > > > > > > Why don't you just grab the mm before you send the signal and then continue > > > > with reaping? You just want to avoid a race where the victim manages to > > > > process fatal signal, start its exit path and mrelease path losing that > > > > race so you rely on the exit path, right? > > > > > > The problem is that process_mrelease() operates on a task obtained from a pidfd. > > > > > > Once the victim process receives the SIGKILL and enters the exit path (exit_mm), > > > the kernel sets task->mm to NULL. > > > > > > Even if we could somehow hold a reference to the mm_struct beforehand, > > > process_mrelease() would still fail because mm_struct via task returns NULL > > > after exit_mm() has been called. > > > > > > Therefore, we cannot simply "grab the mm" before sending the signal and expect > > > process_mrelease() to work after the victim starts exiting. > > > > I do not follow. Why cannot you simply do this > > I misunderstood your point. Do you mean this? > > https://lore.kernel.org/linux-mm/20260421230239.172582-4-minchan@kernel.org/ > > There are more details to figure out. Yes, there are couple of details to iron out. The existing reaping has some hard requirements in place. I am all for relaxing those where possible (ideally without much of special casing for this specific use case) but this is much more viable solution than KILL_MRELEASE you are introducing here. Keep in mind that fundamentally this should be a really as simple as trigger exit_mmap after sending SIGKILL. We are reusing a large part of oom_reaper functionality because it was comfortable but if there are constrains that stand in the way and they make no sense for this usecase then do not sick with them. -- Michal Hocko SUSE Labs