From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.0 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0EE03C11F68 for ; Fri, 2 Jul 2021 05:58:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DB42661424 for ; Fri, 2 Jul 2021 05:58:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229880AbhGBGBF (ORCPT ); Fri, 2 Jul 2021 02:01:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40712 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229733AbhGBGBE (ORCPT ); Fri, 2 Jul 2021 02:01:04 -0400 Received: from mail-pg1-x529.google.com (mail-pg1-x529.google.com [IPv6:2607:f8b0:4864:20::529]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 076C7C061762; Thu, 1 Jul 2021 22:58:31 -0700 (PDT) Received: by mail-pg1-x529.google.com with SMTP id e20so8619849pgg.0; Thu, 01 Jul 2021 22:58:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=Lu7eSsn+Id/N8FajSofs9OS3PuI6JD/yF6zHZnFxH30=; b=KE4M4gZmLORI1SCZ8EN1b30jV6VN5mJtRvPT6vDsEpDkW91sXks9YPQbNFlubvsO4y gaHRfTvhP0r/ZSWm4lKC21SzphxQCqgLCVhVYOYtd+ZOJWKK7PJwoxt5wr8M7YKKJT+F q988TxX1cb7JNBBJHwAkjHx9K7M2LM4mGHubSR5LrACbCXobUk5ilpBZ6Y8TlbYpethL 4mb6QNl1zmpLaLtcokK/tEuTARLF2U1NQ7nzyeTull2X0iLL8mZlJmfs75tTqKLvEXkH 81IbsVH5VpAIwYHDtpRBd+HJik9t+VRKIAi7+gU4fK16JfgBUJvQ/yr8lxZ4iHYMBfD1 Nk4Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to; bh=Lu7eSsn+Id/N8FajSofs9OS3PuI6JD/yF6zHZnFxH30=; b=Ifz4X2c4hMeZ44N3VZz7plOreye/6hT0ohbhGIdz4OvFM290f2I4HY1wGYqbybI/nL 0zysDOET4XWdFG9GWYZOYsPCMEwB5BaMZYGAIUM1tVFcp3JaWk71Ch5nU3jPHjSYObwC uXXuiwPGHTZHyai9uEszDufv3MKzpr/qwfnZAalbW5pwxt/RQL1gzJLyGxjZLnyp7Guw 9+igeFLUq6SoZKYK9LtlYnhbcoyZgNs5T7D5O2c9+S/zpUHypEFoi33pzIeH7hXpb7Nu DKIWEWIXG4ZqswXjHUnc/G+vZ/9/VqXI3V+3nZvEm5SVcMa1tvL296cYuJw3yumuDdbL /EMw== X-Gm-Message-State: AOAM532Gcvxxw5cY9jaezKJkPx0wmRl6ASZxKHEgDPnnYjjPb4gQAMLC Ptua5uHJ0rlaYwCiuegwGtA= X-Google-Smtp-Source: ABdhPJx9iQiOGTL4RIMoRFJF6qMeGkWQTyUsVYDxONye2RFuBrJspgLl5vrzhN1/vvBRYpfBb3fSrw== X-Received: by 2002:a62:5285:0:b029:2e9:e0d5:67dc with SMTP id g127-20020a6252850000b02902e9e0d567dcmr3792309pfb.79.1625205511403; Thu, 01 Jul 2021 22:58:31 -0700 (PDT) Received: from google.com ([2620:15c:211:201:e476:fcd4:d1bf:22a2]) by smtp.gmail.com with ESMTPSA id k13sm1834882pfu.57.2021.07.01.22.58.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Jul 2021 22:58:30 -0700 (PDT) Sender: Minchan Kim Date: Thu, 1 Jul 2021 22:58:28 -0700 From: Minchan Kim To: Luis Chamberlain Cc: gregkh@linuxfoundation.org, jeyu@kernel.org, ngupta@vflare.org, sergey.senozhatsky.work@gmail.com, rafael@kernel.org, axboe@kernel.dk, tj@kernel.org, mbenes@suse.com, jpoimboe@redhat.com, tglx@linutronix.de, keescook@chromium.org, jikos@kernel.org, rostedt@goodmis.org, peterz@infradead.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 2/2] zram: fix deadlock with sysfs attribute usage and module removal Message-ID: References: <20210702043716.2692247-1-mcgrof@kernel.org> <20210702043716.2692247-3-mcgrof@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210702043716.2692247-3-mcgrof@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Thu, Jul 01, 2021 at 09:37:16PM -0700, Luis Chamberlain wrote: > When sysfs attributes use a lock also used on module removal we can > potentially deadlock. This happens when for instance a sysfs file on > a driver is used, then at the same time we have module removal call > trigger. The module removal call code holds a lock, and then the sysfs > file entry waits for the same lock. While holding the lock the module > removal tries to remove the sysfs entries, but these cannot be removed > yet as one is waiting for a lock. This won't complete as the lock is > already held. Likewise module removal cannot complete, and so we deadlock. > > To fix this we just *try* to get a refcount to the module when a shared > lock is used, prior to mucking with a sysfs attribute. If this fails we > just give up right away. > > We use a try method as a full lock means we'd then make our sysfs > attributes busy us out from possible module removal, and so userspace > could force denying module removal, a silly form of "DOS" against module > removal. A try lock on the module removal ensures we give priority to > module removal and interacting with sysfs attributes only comes second. > Using a full lock could mean for instance that if you don't stop poking > at sysfs files you cannot remove a module. > > This deadlock was first reported with the zram driver, a sketch of how > this can happen follows: > > CPU A CPU B > whatever_store() > module_unload > mutex_lock(foo) > mutex_lock(foo) > del_gendisk(zram->disk); > device_del() > device_remove_groups() > > In this situation whatever_store() is waiting for the mutex foo to > become unlocked, but that won't happen until module removal is complete. > But module removal won't complete until the sysfs file being poked > completes which is waiting for a lock already held. > > This is a generic kernel issue with sysfs files which use any lock also > used on module removal. Different generic solutions have been proposed. > One approach proposed is by directly by augmenting attributes with module > information [0]. This patch implements a solution by adding macros with > the prefix MODULE_DEVICE_ATTR_*() which accomplish the same. Until we > don't have a generic agreed upon solution for this shared between drivers, > we must implement a fix for this on each driver. > > We make zram use the new MODULE_DEVICE_ATTR_*() helpers, and completely > open code the solution for class attributes as there are only a few of > those. > > This issue can be reproduced easily on the zram driver as follows: > > Loop 1 on one terminal: > > while true; > do modprobe zram; > modprobe -r zram; > done > > Loop 2 on a second terminal: > while true; do > echo 1024 > /sys/block/zram0/disksize; > echo 1 > /sys/block/zram0/reset; > done > > Without this patch we end up in a deadlock, and the following > stack trace is produced which hints to us what the issue was: > > INFO: task bash:888 blocked for more than 120 seconds. > Tainted: G E 5.12.0-rc1-next-20210304+ #4 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > task:bash state:D stack: 0 pid: 888 ppid: 887 flags: > Call Trace: > __schedule+0x2e4/0x900 > schedule+0x46/0xb0 > schedule_preempt_disabled+0xa/0x10 > __mutex_lock.constprop.0+0x2c3/0x490 > ? _kstrtoull+0x35/0xd0 > reset_store+0x6c/0x160 [zram] > kernfs_fop_write_iter+0x124/0x1b0 > new_sync_write+0x11c/0x1b0 > vfs_write+0x1c2/0x260 > ksys_write+0x5f/0xe0 > do_syscall_64+0x33/0x80 > entry_SYSCALL_64_after_hwframe+0x44/0xae > RIP: 0033:0x7f34f2c3df33 > RSP: 002b:00007ffe751df6e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 > RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 00007f34f2c3df33 > RDX: 0000000000000002 RSI: 0000561ccb06ec10 RDI: 0000000000000001 > RBP: 0000561ccb06ec10 R08: 000000000000000a R09: 0000000000000001 > R10: 0000561ccb157590 R11: 0000000000000246 R12: 0000000000000002 > R13: 00007f34f2d0e6a0 R14: 0000000000000002 R15: 00007f34f2d0e8a0 > INFO: task modprobe:1104 can't die for more than 120 seconds. > task:modprobe state:D stack: 0 pid: 1104 ppid: 916 flags: > Call Trace: > __schedule+0x2e4/0x900 > schedule+0x46/0xb0 > __kernfs_remove.part.0+0x228/0x2b0 > ? finish_wait+0x80/0x80 > kernfs_remove_by_name_ns+0x50/0x90 > remove_files+0x2b/0x60 > sysfs_remove_group+0x38/0x80 > sysfs_remove_groups+0x29/0x40 > device_remove_attrs+0x4a/0x80 > device_del+0x183/0x3e0 > ? mutex_lock+0xe/0x30 > del_gendisk+0x27a/0x2d0 > zram_remove+0x8a/0xb0 [zram] > ? hot_remove_store+0xf0/0xf0 [zram] > zram_remove_cb+0xd/0x10 [zram] > idr_for_each+0x5e/0xd0 > destroy_devices+0x39/0x6f [zram] > __do_sys_delete_module+0x190/0x2a0 > do_syscall_64+0x33/0x80 > entry_SYSCALL_64_after_hwframe+0x44/0xae > RIP: 0033:0x7f32adf727d7 > RSP: 002b:00007ffc08bb38a8 EFLAGS: 00000206 ORIG_RAX: 00000000000000b0 > RAX: ffffffffffffffda RBX: 000055eea23cbb10 RCX: 00007f32adf727d7 > RDX: 0000000000000000 RSI: 0000000000000800 RDI: 000055eea23cbb78 > RBP: 000055eea23cbb10 R08: 0000000000000000 R09: 0000000000000000 > R10: 00007f32adfe5ac0 R11: 0000000000000206 R12: 000055eea23cbb78 > R13: 0000000000000000 R14: 0000000000000000 R15: 000055eea23cbc20 > > [0] https://lkml.kernel.org/r/20210401235925.GR4332@42.do-not-panic.com > > Signed-off-by: Luis Chamberlain Acked-by: Minchan Kim Much simple/clean now. Thanks for persuing the effort.