From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 016E3369203; Fri, 1 May 2026 21:17:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777670273; cv=none; b=RT8OOp0LLGhTAbsUNoKZpDhlj6oc8q9TRyhiUg9VBx5IVXiRLug9EB3c/GTtC8KuQfbS3rkTOgvvgntx4fEQr7uqhynpoCdvkHsutYxPCMadTU8kRoo+ljKEysK1uYgCNk3ByxG9ZKB0uADHGbIsD6sC3cWG9hsjUGkm9CB+tdw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777670273; c=relaxed/simple; bh=vlOkMj8GrldfLKQy/WTdxUydoj8upb7F0jPdovFF7F0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=b8hLSvv+l1aZNp/YFKWuIgcDXnQXny0DFQYPjd1JkTIttIuEVMg0U1o/XiKEkWYV8C7pV8lAAK59bALQwyOQDkaIT0TONv6x81TtLdLRz4c4dKqLlfB2U3CJS+YZwuIW58//g3L79ji2aT45QH+BXKektT2utBsURG6QFPKTCOs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jBCThL0Z; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="jBCThL0Z" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3201CC2BCB4; Fri, 1 May 2026 21:17:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777670272; bh=vlOkMj8GrldfLKQy/WTdxUydoj8upb7F0jPdovFF7F0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=jBCThL0ZUOciVlUdDPlkZOk2cwVOOm8Tbr2iNkMf1UGQrhNwVAoYKLFZTpPGFIugP CqIPbpV2kLYCf98CGWmWPPj6kC5jgCpM6j2ptLOpMUKKF3lFhrXG1YmCUhVoADAayI kJl0abVkEp8vQhV144UzJ7SeaBM5+Nrw3EneesVRY12GOeH95mQQuElzJpImNe8ygq ZIwcBr2eGznEeLx7R3QktlCeMAd6ttF4Ov8uCuxvX/cvkctsDe/NY8BkUl7IBTC+EY FEPU5ZI3zs5pRja1ojW9ao3vP6IaxyzGTCsDFql6UajD++8QUl6QYku9G8t22L60lr ElPjU2QMNNO7Q== Date: Fri, 1 May 2026 14:17:50 -0700 From: Minchan Kim To: Michal Hocko , Christian Brauner Cc: akpm@linux-foundation.org, hca@linux.ibm.com, linux-s390@vger.kernel.org, david@kernel.org, brauner@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, surenb@google.com, timmurray@google.com Subject: Re: [PATCH v2] mm: process_mrelease: introduce PROCESS_MRELEASE_REAP_KILL flag Message-ID: References: <20260429211359.3829683-1-minchan@kernel.org> Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Thu, Apr 30, 2026 at 11:55:54AM +0200, Michal Hocko wrote: > On Wed 29-04-26 14:13:59, Minchan Kim wrote: > > This policy differs from the global OOM killer, which kills all processes > > sharing the same mm to guarantee memory reclamation at all costs (preventing > > system hangs). > > Incorrect, we do the same for memcg OOM killer as well. This is not > about preventing system hands. But rather to > > > However, process_mrelease() is invoked by userspace policy. > > If it fails due to sharing, userspace can simply adapt and select another > > victim process (such as another background app in Android case) to release > > memory. We do not need to force success or affect processes that were not > > targeted. > > This is a wrong justification for the proposed semantic. You seem to be > assuming this is just fine rather than this would be problematic for > reasons a), b) and c). If there are no strong reasons _against_ > following the global policy then we should stick with it. There are very > good reasons why we are doing that on the global level. > > If for no other reasons then the proposed semantic severly criples the > shared MM case. You are left with a racy kill and call process_mrelease > approach. You certainly do not want to allow a simple way for tasks to > evade your LMK, do you? So just choose something else is a very bad > approach. > > So unless you are aware of a specific reason(s) where collective kill is a > clearly an incorrect behavior then I believe the proper way is to kill > all processes sharing the mm (unless you are crossing any security > boundary when doing that). I agree that in the case of a global or memcg OOM, the kernel deals with an emergency, system-wide crisis where killing all sibling processes sharing the same mm is an absolute necessity for system survival, bypassing user-space privilege screening. However, process_mrelease() is an explicit user-space initiated system call, and I am still hesitant to place that same raw, destructive policy blindly at the UAPI syscall level even though I don't know of any known security issues right now. If we really want to go that way for the collective kill, at least, we should evaluate signal authorization (kill permission) against *every single* sibling process beforehand instead of only the target task of process_mrelease. Do you agree? Also, I wonder what the signal/process maintainer thinks about this approach. Christian Brauner ?