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 1D55428E8; Tue, 20 Aug 2024 19:34:16 +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=1724182457; cv=none; b=aOsi7zlmlLVds2a9mNZwePRKKEExNH9+ww53HgX8lFoRev2r/MrIIhX/sAuxwbYHhY0xa2bpHgMqJO3kLVTqeHfnBbzHotmPWhrFuHMAt3oRFwXbCoCsg9mYpbhex+kMajv/W1urrTeN85akZyiyY8Gk/u1xmQ+x5DCnRDyS8hU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724182457; c=relaxed/simple; bh=ztkY1HcRzYZPhdNOGcVyvUZWwCzGOeoC3a5BlTiOty8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=HmJx1TVYiR6aOG9vI+VhuNpdM14NgMY76zK50OQzmZF7ncIkNVwcR/QLbEuiH3w06BqXaLkdrBxawHGn1/c13ekhDM54WtNEkO2l8GtH7pse9W77Y9ni7HrIztlAVxlIDc963sP7u128F+orDZ+NYLDROaxsNafBSS5tc25iGlA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ufF3CqrK; 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="ufF3CqrK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3E045C4AF15; Tue, 20 Aug 2024 19:34:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1724182456; bh=ztkY1HcRzYZPhdNOGcVyvUZWwCzGOeoC3a5BlTiOty8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ufF3CqrKmgREyHzpn6s40n4gwbUKiBn3qYB54yCPjq5LYv4aLjVMy1ChiZalXul// jv1ahPCJhMGX6eEsoKZHeIGw27bmCwNDvJB1muHRgl0C3BDWaEYfp0UFmdfT8GgrcT GF8NBVLrnkXe60xwRXdae6uljlJd2lLFqG7LJYVphrzXxhyswKygIHWVaywdiBq4Df w3B7Hgn/DYMhTwhsgyUmA47XYlJhGhTSUqTjAmJCxgOqFMa3S8mI5zKIKfzLrnwbi5 xCPAOofu9jst2h2B/nZ2jgeM6KSSkX73aNChZHh8Ly2k/F6s7jR7zQ95NMfwdRRK6E ldb9rbpIIyf6Q== Date: Tue, 20 Aug 2024 12:34:14 -0700 From: Eric Biggers To: Christian Brauner Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Oleg Nesterov , Aleksa Sarai , Tycho Andersen , Daan De Meyer , Tejun Heo , stable@vger.kernel.org Subject: Re: [PATCH] pidfd: prevent creation of pidfds for kthreads Message-ID: <20240820193414.GA1178@sol.localdomain> References: <20240731-gleis-mehreinnahmen-6bbadd128383@brauner> <20240818035818.GA1929@sol.localdomain> <20240819-staudamm-rederei-cb7092f54e76@brauner> Precedence: bulk X-Mailing-List: stable@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: <20240819-staudamm-rederei-cb7092f54e76@brauner> On Mon, Aug 19, 2024 at 10:41:15AM +0200, Christian Brauner wrote: > On Sat, Aug 17, 2024 at 08:58:18PM GMT, Eric Biggers wrote: > > Hi Christian, > > > > On Wed, Jul 31, 2024 at 12:01:12PM +0200, Christian Brauner wrote: > > > It's currently possible to create pidfds for kthreads but it is unclear > > > what that is supposed to mean. Until we have use-cases for it and we > > > figured out what behavior we want block the creation of pidfds for > > > kthreads. > > > > > > Fixes: 32fcb426ec00 ("pid: add pidfd_open()") > > > Cc: stable@vger.kernel.org > > > Signed-off-by: Christian Brauner > > > --- > > > kernel/fork.c | 25 ++++++++++++++++++++++--- > > > 1 file changed, 22 insertions(+), 3 deletions(-) > > > > Unfortunately this commit broke systemd-shutdown's ability to kill processes, > > which makes some filesystems no longer get unmounted at shutdown. > > > > It looks like systemd-shutdown relies on being able to create a pidfd for any > > process listed in /proc (even a kthread), and if it gets EINVAL it treats it a > > fatal error and stops looking for more processes... > > Thanks for the report! > I talked to Daan De Meyer who made that change and he said that this > must a systemd version that hasn't gotten his fixes yet. In any case, if > this causes regression then I'll revert it right now. See the appended > revert. Thanks for queueing up a revert. This was on systemd 256.4 which was released less than a month ago. I'm not sure what systemd fix you are talking about. Looking at killall() in src/shared/killall.c on the latest "main" branch of systemd, it calls proc_dir_read_pidref() => pidref_set_pid() => pidfd_open(), and EINVAL gets passed back up to killall() and treated as a fatal error. ignore_proc() skips kernel threads but is executed too late. I didn't test it, so I could be wrong, but based on the code it does not appear to be fixed. - Erici