From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f200.google.com (mail-wr0-f200.google.com [209.85.128.200]) by kanga.kvack.org (Postfix) with ESMTP id 8BA996B0033 for ; Fri, 24 Nov 2017 07:21:51 -0500 (EST) Received: by mail-wr0-f200.google.com with SMTP id z14so9398600wrb.12 for ; Fri, 24 Nov 2017 04:21:51 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id n10si836917edf.443.2017.11.24.04.21.50 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 24 Nov 2017 04:21:50 -0800 (PST) Date: Fri, 24 Nov 2017 13:21:48 +0100 From: Michal Hocko Subject: Re: [PATCH v2 1/2] mm,vmscan: Make unregister_shrinker() no-op if register_shrinker() failed. Message-ID: <20171124122148.qevmiogh3pzr4zix@dhcp22.suse.cz> References: <1511523385-6433-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1511523385-6433-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> Sender: owner-linux-mm@kvack.org List-ID: To: Tetsuo Handa Cc: linux-mm@kvack.org, akpm@linux-foundation.org, Al Viro , Glauber Costa , syzbot On Fri 24-11-17 20:36:24, Tetsuo Handa wrote: > Syzbot caught an oops at unregister_shrinker() because combination of > commit 1d3d4437eae1bb29 ("vmscan: per-node deferred work") and fault > injection made register_shrinker() fail and the caller of > register_shrinker() did not check for failure. > > ---------- > [ 554.881422] FAULT_INJECTION: forcing a failure. > [ 554.881422] name failslab, interval 1, probability 0, space 0, times 0 > [ 554.881438] CPU: 1 PID: 13231 Comm: syz-executor1 Not tainted 4.14.0-rc8+ #82 > [ 554.881443] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > [ 554.881445] Call Trace: > [ 554.881459] dump_stack+0x194/0x257 > [ 554.881474] ? arch_local_irq_restore+0x53/0x53 > [ 554.881486] ? find_held_lock+0x35/0x1d0 > [ 554.881507] should_fail+0x8c0/0xa40 > [ 554.881522] ? fault_create_debugfs_attr+0x1f0/0x1f0 > [ 554.881537] ? check_noncircular+0x20/0x20 > [ 554.881546] ? find_next_zero_bit+0x2c/0x40 > [ 554.881560] ? ida_get_new_above+0x421/0x9d0 > [ 554.881577] ? find_held_lock+0x35/0x1d0 > [ 554.881594] ? __lock_is_held+0xb6/0x140 > [ 554.881628] ? check_same_owner+0x320/0x320 > [ 554.881634] ? lock_downgrade+0x990/0x990 > [ 554.881649] ? find_held_lock+0x35/0x1d0 > [ 554.881672] should_failslab+0xec/0x120 > [ 554.881684] __kmalloc+0x63/0x760 > [ 554.881692] ? lock_downgrade+0x990/0x990 > [ 554.881712] ? register_shrinker+0x10e/0x2d0 > [ 554.881721] ? trace_event_raw_event_module_request+0x320/0x320 > [ 554.881737] register_shrinker+0x10e/0x2d0 > [ 554.881747] ? prepare_kswapd_sleep+0x1f0/0x1f0 > [ 554.881755] ? _down_write_nest_lock+0x120/0x120 > [ 554.881765] ? memcpy+0x45/0x50 > [ 554.881785] sget_userns+0xbcd/0xe20 > (...snipped...) > [ 554.898693] kasan: CONFIG_KASAN_INLINE enabled > [ 554.898724] kasan: GPF could be caused by NULL-ptr deref or user memory access > [ 554.898732] general protection fault: 0000 [#1] SMP KASAN > [ 554.898737] Dumping ftrace buffer: > [ 554.898741] (ftrace buffer empty) > [ 554.898743] Modules linked in: > [ 554.898752] CPU: 1 PID: 13231 Comm: syz-executor1 Not tainted 4.14.0-rc8+ #82 > [ 554.898755] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > [ 554.898760] task: ffff8801d1dbe5c0 task.stack: ffff8801c9e38000 > [ 554.898772] RIP: 0010:__list_del_entry_valid+0x7e/0x150 > [ 554.898775] RSP: 0018:ffff8801c9e3f108 EFLAGS: 00010246 > [ 554.898780] RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000 > [ 554.898784] RDX: 0000000000000000 RSI: ffff8801c53c6f98 RDI: ffff8801c53c6fa0 > [ 554.898788] RBP: ffff8801c9e3f120 R08: 1ffff100393c7d55 R09: 0000000000000004 > [ 554.898791] R10: ffff8801c9e3ef70 R11: 0000000000000000 R12: 0000000000000000 > [ 554.898795] R13: dffffc0000000000 R14: 1ffff100393c7e45 R15: ffff8801c53c6f98 > [ 554.898800] FS: 0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000 > [ 554.898804] CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033 > [ 554.898807] CR2: 00000000dbc23000 CR3: 00000001c7269000 CR4: 00000000001406e0 > [ 554.898813] DR0: 0000000020000000 DR1: 0000000020000000 DR2: 0000000000000000 > [ 554.898816] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600 > [ 554.898818] Call Trace: > [ 554.898828] unregister_shrinker+0x79/0x300 > [ 554.898837] ? perf_trace_mm_vmscan_writepage+0x750/0x750 > [ 554.898844] ? down_write+0x87/0x120 > [ 554.898851] ? deactivate_super+0x139/0x1b0 > [ 554.898857] ? down_read+0x150/0x150 > [ 554.898864] ? check_same_owner+0x320/0x320 > [ 554.898875] deactivate_locked_super+0x64/0xd0 > [ 554.898883] deactivate_super+0x141/0x1b0 > ---------- > > Since allowing register_shrinker() callers to call unregister_shrinker() > when register_shrinker() failed can simplify error recovery path, this > patch makes unregister_shrinker() no-op when register_shrinker() failed. Well, the primary point of this patch is to not blow up, in the first place. It is not to woraround missing register_shrinker handling which what one could understand from the above. Yes we are making it noop because it is easier for users but they still _have_ to check the error path otherwise we have silent memory pressure issues potentially. > Since we can encourage register_shrinker() callers to check for failure > by marking register_shrinker() as __must_check, unregister_shrinker() > can stay silent. I am not sure __must_check is the right way. We already do get allocation warning if the registration fails so silent unregister is acceptable. Unchecked register_shrinker is a bug like any other unchecked error path. > Signed-off-by: Tetsuo Handa > Reported-by: syzbot > Cc: Glauber Costa > Cc: Al Viro With the changelog updated Acked-by: Michal Hocko > --- > mm/vmscan.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 6a5a72b..d01177b 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -297,6 +297,8 @@ int register_shrinker(struct shrinker *shrinker) > */ > void unregister_shrinker(struct shrinker *shrinker) > { > + if (!shrinker->nr_deferred) > + return; > down_write(&shrinker_rwsem); > list_del(&shrinker->list); > up_write(&shrinker_rwsem); > -- > 1.8.3.1 > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org