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 C0012137929; Tue, 16 Apr 2024 19:18:05 +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=1713295085; cv=none; b=mIDV8M1QnkUtqGLlavM/3AAGP450EnjgA0IhgR8+wsvFgHwvMZvfvW59+aUivlVweCVxp4LgpqOl+HFwOCduCrnffXvW9euXLzPot3JHvCmy1MDlOuH87hzB2C0w/fF6WLnTfsqX2ZB0Rgl0ylnm4OfJYm5DfOwxWx7+Rn7Q9i4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713295085; c=relaxed/simple; bh=qe83P9vvTKzKa5UvpEdn6fNXNpGNSmqGdNylsccrOPg=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=pm/ygnanzSTvIgIRYNRTp7DMeJCOTN7nTXcUUTsot72cHuLgJL9ymmeKZPoWBbezfsyXNWB7CraMTGwgcIfuv5W0VXZoughMOji3rKAKzPrm5Hgw67nr4fMJqvcoz2qFdI9zvb936fA3CM7rOv69Ky3ICtR0gc1OztwSj3gg/2E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=pVdheGOo; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="pVdheGOo" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B7D88C113CE; Tue, 16 Apr 2024 19:18:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1713295085; bh=qe83P9vvTKzKa5UvpEdn6fNXNpGNSmqGdNylsccrOPg=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=pVdheGOoICvekvJn1ImFKQUiCCrvaWXTHv0NGii/S5H8qa4b/gMw7RUsRncLQGheH QoQw8hNH+BtYx0X0PSDPk3yfINo8dnrUVtBOdlff6gODI3AzNz/FgYJ1jN9hI5cLh5 oR3RfafPTtgJoGL6I1VHhoa15sMYx824E9SFr3yk= Date: Tue, 16 Apr 2024 12:18:04 -0700 From: Andrew Morton To: Christian Heusel Cc: Seth Jennings , Dan Streetman , Vitaly Wool , linux-mm@kvack.org, linux-kernel@vger.kernel.org, David Runge , "Richard W.M. Jones" , Mark W , regressions@lists.linux.dev, Johannes Weiner , Yosry Ahmed , Nhat Pham , Chengming Zhou Subject: Re: [REGRESSION] Null pointer dereference while shrinking zswap Message-Id: <20240416121804.a46c4174f6cec30ab51f18e5@linux-foundation.org> In-Reply-To: <3iccc6vjl5gminut3lvpl4va2lbnsgku5ei2d7ylftoofy3n2v@gcfdvtsq6dx2> References: <3iccc6vjl5gminut3lvpl4va2lbnsgku5ei2d7ylftoofy3n2v@gcfdvtsq6dx2> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 16 Apr 2024 14:19:24 +0200 Christian Heusel wrote: > Hello everyone, > > while rebuilding a few packages in Arch Linux we have recently come > across a regression in the linux kernel which was made visible by a test > failure in libguestfs[0], where the booted kernel showed a Call Trace > like the following one: > > [ 218.738568] CPU: 0 PID: 167 Comm: guestfsd Not tainted 6.7.0-rc4-1-mainline-00158-gb5ba474f3f51 #1 bf39861cf50acae7a79c534e25532f28afe4e593^M (cc more zswap people) Fairly old kernel. We might have fixed it since then, but it would be good to know what fixed this, for backporting reasons. > [ 218.739007] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS Arch Linux 1.16.3-1-1 04/01/2014^M > [ 218.739787] RIP: 0010:memcg_page_state+0x9/0x30^M > [ 218.740299] Code: 0d b8 ff ff 66 66 2e 0f 1f 84 00 00 00 00 00 66 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 66 0f 1f 00 0f 1f 44 00 00 <48> 8b 87 00 06 00 00 48 63 f6 31 d2 48 8b 04 f0 48 85 c0 48 0f 48^M > [ 218.740727] RSP: 0018:ffffb5fa808dfc10 EFLAGS: 00000202^M > [ 218.740862] RAX: 0000000000000000 RBX: ffffb5fa808dfce0 RCX: 0000000000000002^M > [ 218.741016] RDX: 0000000000000001 RSI: 0000000000000033 RDI: 0000000000000000^M > [ 218.741168] RBP: 0000000000000000 R08: ffff976681ff8000 R09: 0000000000000000^M > [ 218.741322] R10: 0000000000000001 R11: ffff9766833f9d00 R12: ffff9766ffffe780^M > [ 218.742167] R13: 0000000000000000 R14: ffff976680cc1800 R15: ffff976682204d80^M > [ 218.742376] FS: 00007f1479d9f540(0000) GS:ffff9766fbc00000(0000) knlGS:0000000000000000^M > [ 218.742569] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033^M > [ 218.743256] CR2: 0000000000000600 CR3: 0000000103606000 CR4: 0000000000750ef0^M > [ 218.743494] PKRU: 55555554^M > [ 218.743593] Call Trace:^M > [ 218.743733] ^M > [ 218.743847] ? __die+0x23/0x70^M > [ 218.743957] ? page_fault_oops+0x171/0x4e0^M > [ 218.744056] ? free_unref_page+0xf6/0x180^M > [ 218.744458] ? exc_page_fault+0x7f/0x180^M > [ 218.744551] ? asm_exc_page_fault+0x26/0x30^M > [ 218.744684] ? memcg_page_state+0x9/0x30^M > [ 218.744779] zswap_shrinker_count+0x9d/0x110^M > [ 218.744896] do_shrink_slab+0x3a/0x360^M > [ 218.744990] shrink_slab+0xc7/0x3c0^M > [ 218.745609] drop_slab+0x85/0x140^M > [ 218.745691] drop_caches_sysctl_handler+0x7e/0xd0^M > [ 218.745799] proc_sys_call_handler+0x1c0/0x2e0^M > [ 218.745912] vfs_write+0x23d/0x400^M > [ 218.745998] ksys_write+0x6f/0xf0^M > [ 218.746080] do_syscall_64+0x64/0xe0^M > [ 218.746169] ? exit_to_user_mode_prepare+0x132/0x1f0^M > [ 218.746873] entry_SYSCALL_64_after_hwframe+0x6e/0x76^M > > The regression is present in the mainline kernel and also was > independently reported to the redhat bugtracker[1]. > > I have bisected (see log[2]) the regression between v6.9-rc4 and v6.6 > and have landed on the following results (removed unrelated test commit) > as remainders since some of the commits were not buildable for me: > - 7108cc3f765c ("mm: memcg: add per-memcg zswap writeback stat") > - a65b0e7607cc ("zswap: make shrinking memcg-aware") > - b5ba474f3f51 ("zswap: shrink zswap pool based on memory pressure") > > I have decided on good/bad commits with the relevant libguestfs tests, > but I think the reproducer in the redhat bugzilla is simpler (although I > only became aware of it during the bisection and therefore didn't test > it myself): > > LIBGUESTFS_MEMSIZE=4096 LIBGUESTFS_DEBUG=1 LIBGUESTFS_TRACE=1 make -C /build/libguestfs/src/libguestfs-1.52.0/tests -k check TESTS=c-api/tests > > I hope I have included everything needed to debug this further, if there > is more to add I'm happy to provide more details! > > Cheers, > Christian > > [0]: https://github.com/libguestfs/libguestfs/issues/139 > [1]: https://bugzilla.redhat.com/show_bug.cgi?id=2275252 > [2]: https://gist.github.com/christian-heusel/d5095c36b72ae90871e27dfed32ddc46