From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 D8C92397E92; Thu, 25 Jun 2026 10:57:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782385031; cv=none; b=KHcTKM2Y1cFxJ2uF4MBts+UHkdOm3URVypwuUkhE6O3N7MBhGS8EEhLsJkJKSL0OQ2YXh3AF3cdiJ5V5FDk2BSkLas11U3QzBqX6Olg1Tivw10DD+nUn3JxR2AUIejHdSvJO5qYTWWptNaHBOklakCfIOcFRCI8hJOZ2K3SKXzE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782385031; c=relaxed/simple; bh=9KF5R6dD/IJCSXWxZtgQlOGoHXYnhsCeEF2a4cPBKq4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=KViSX07IXrIcYBi28bmPD4ADafOP3LqINW8JZ3vL+ov7WJNuKA6oDTB8UtAv9TajfPK2g4+2d+qJBdNm1+sBPMmQnuRGRpy8DJyF0ZrupGtofbvz73BvEFfRXcbSA7WbfZxrjExX3I6IpLSBrqXKULrDu1F0ECwPtrWdyxGBVBE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ND0O6TyC; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ND0O6TyC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C5F4B1F000E9; Thu, 25 Jun 2026 10:57:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782385030; bh=1JCXB0zNTf/AELeBd7FV26+x3FLfZvl38bsfAk9MOdk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=ND0O6TyC0KNxiweXNCoigX32kil+sQ32QIEurWStEiE7oO1t0Xi/VjBNYxe9ww7Jg I/tO1nBlkG2C7jGl1yBZACb6GxwZu/FgqqFbS0C0lsJnPqoGTR5ofb3NZJgyiybKNe Sc+XPw0a9RAbu46u7D+uGg3HOAFbr0NF0sKXEcOvT4QZjIv2cPgZrdeQVpahwUlPc1 A2o4UbJB+tP4+pGF5PLi7FNmyAQJCo3Ny5ca3m0M9gS8rXqSSh+kw3yHrgoDuWcuZA gZaABt2L+RfzCa+HYo+FsJkjOCcSP9weB5BwzfDQ0gGkXR4rjh6YXEATccAiGajWQq mmVGY/hwLl3tA== Message-ID: <9105c433-44a7-4e8f-bacb-def93d11a7f2@kernel.org> Date: Thu, 25 Jun 2026 12:57:02 +0200 Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4] coredump: Add /proc//coredump_pre_exit for pre-exit before dumping To: Christian Brauner , Mike Rapoport , Lorenzo Stoakes , mjguzik@gmail.com, pfalcato@suse.de, ebiederm@xmission.com, viro@zeniv.linux.org.uk, jack@suse.cz, jlayton@kernel.org, chuck.lever@oracle.com, alex.aring@gmail.com, arnd@arndb.de, keescook@chromium.org, mcgrof@kernel.org, j.granados@samsung.com, allen.lkml@gmail.com Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Xin Zhao , linux-mm@kvack.org References: <20260624145552.70143-1-jackzxcui1989@163.com> <20260625-wappnen-drohbrief-wermutstropfen-c53538f01547@brauner> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit >> + >> #define F_DUPFD 0 /* dup */ >> #define F_GETFD 1 /* get close_on_exec */ >> #define F_SETFD 2 /* set/clear close_on_exec */ >> diff --git a/kernel/fork.c b/kernel/fork.c >> index a679b2448234..84f1ee7f32cf 100644 >> --- a/kernel/fork.c >> +++ b/kernel/fork.c >> @@ -1030,6 +1030,18 @@ static int __init coredump_filter_setup(char *s) >> >> __setup("coredump_filter=", coredump_filter_setup); >> >> +static unsigned long default_dump_pre_exit; >> + >> +static int __init coredump_pre_exit_setup(char *s) >> +{ >> + default_dump_pre_exit = >> + (simple_strtoul(s, NULL, 0) << MMF_DUMP_PRE_EXIT_SHIFT) & >> + MMF_DUMP_PRE_EXIT_MASK; >> + return 1; >> +} >> + >> +__setup("coredump_pre_exit=", coredump_pre_exit_setup); > > This makes no sense. I think you really need to sit down and think about > a design for this that doesn't introduce state machinery for boot, mm, > and the VFS in one shot to solve a fringe problem... Staring at exit_mmap_mapped_shared(), ... this looks rather hacky ("let's fake munmap and set some magical flags"). We're essentially saying "we don't want (pretty much) anything that's MAP_SHARED in the coredump". And for some reason someone should configure that, that's a rather weird toggle tbh. And the granularity ("file-backed shared memory") is completely odd. Aren't there other ways we could optimize this internally? Like, if we know that a process is dead and cannot run anymore, downgrade writes to reads (and make sure we block GUP write attempts accordingly), or would that also not be sufficient? Another thought: fs/coredump.c calls get_dump_page(). get_dump_page() will not fault in any memory. So if a page is not in the page tables at the time of the dump, it will not get included in the coredump. Which means, that whether most non-anonymous memory will be included in a coredump is already like playing the lottery. This is true for MAP_SHARED file mappings and MAP_PRIVATE file mappings without private modifications. Which makes me wonder: How much is tooling relying on file-backed pages to end up in a coredump? -- Cheers, David