From: Anand Jain <anand.jain@oracle.com>
To: dsterba@suse.cz, linux-btrfs@vger.kernel.org
Subject: Re: [PATCH v4 1/3] btrfs: scrub: fix circular locking dependency warning
Date: Thu, 14 Feb 2019 00:02:28 +0800 [thread overview]
Message-ID: <ce95f62f-dcf3-5364-3449-b4e23f28dd5f@oracle.com> (raw)
In-Reply-To: <20190212164522.GE2900@twin.jikos.cz>
On 2/13/19 12:45 AM, David Sterba wrote:
> On Wed, Jan 30, 2019 at 02:45:00PM +0800, Anand Jain wrote:
>> Circular locking dependency check reports warning[1], that's because
>> the btrfs_scrub_dev() calls the stack #0 below with, the
>> fs_info::scrub_lock held. The test case leading to this warning..
>>
>> mkfs.btrfs -fq /dev/sdb && mount /dev/sdb /btrfs
>> btrfs scrub start -B /btrfs
>>
>> In fact we have fs_info::scrub_workers_refcnt to tack if the init and
>> destroy of the scrub workers are needed. So once we have incremented
>> and decremented the fs_info::scrub_workers_refcnt value in the thread,
>> its ok to drop the scrub_lock, and then actually do the
>> btrfs_destroy_workqueue() part. So this patch drops the scrub_lock
>> before calling btrfs_destroy_workqueue().
>>
>> [1]
>> [ 76.146826] ======================================================
>> [ 76.147086] WARNING: possible circular locking dependency detected
>> [ 76.147316] 4.20.0-rc3+ #41 Not tainted
>> [ 76.147489] ------------------------------------------------------
>> [ 76.147722] btrfs/4065 is trying to acquire lock:
>> [ 76.147984] 0000000038593bc0 ((wq_completion)"%s-%s""btrfs",
>> name){+.+.}, at: flush_workqueue+0x70/0x4d0
>> [ 76.148337]
>> but task is already holding lock:
>> [ 76.148594] 0000000062392ab7 (&fs_info->scrub_lock){+.+.}, at:
>> btrfs_scrub_dev+0x316/0x5d0 [btrfs]
>> [ 76.148909]
>> which lock already depends on the new lock.
>>
>> [ 76.149191]
>> the existing dependency chain (in reverse order) is:
>> [ 76.149446]
>> -> #3 (&fs_info->scrub_lock){+.+.}:
>> [ 76.149707] btrfs_scrub_dev+0x11f/0x5d0 [btrfs]
>> [ 76.149924] btrfs_ioctl+0x1ac3/0x2d80 [btrfs]
>> [ 76.150216] do_vfs_ioctl+0xa9/0x6d0
>> [ 76.150468] ksys_ioctl+0x60/0x90
>> [ 76.150716] __x64_sys_ioctl+0x16/0x20
>> [ 76.150911] do_syscall_64+0x50/0x180
>> [ 76.151182] entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> [ 76.151469]
>> -> #2 (&fs_devs->device_list_mutex){+.+.}:
>> [ 76.151851] reada_start_machine_worker+0xca/0x3f0 [btrfs]
>> [ 76.152195] normal_work_helper+0xf0/0x4c0 [btrfs]
>> [ 76.152489] process_one_work+0x1f4/0x520
>> [ 76.152751] worker_thread+0x46/0x3d0
>> [ 76.153715] kthread+0xf8/0x130
>> [ 76.153912] ret_from_fork+0x3a/0x50
>> [ 76.154178]
>> -> #1 ((work_completion)(&work->normal_work)){+.+.}:
>> [ 76.154575] worker_thread+0x46/0x3d0
>> [ 76.154828] kthread+0xf8/0x130
>> [ 76.155108] ret_from_fork+0x3a/0x50
>> [ 76.155357]
>> -> #0 ((wq_completion)"%s-%s""btrfs", name){+.+.}:
>> [ 76.155751] flush_workqueue+0x9a/0x4d0
>> [ 76.155911] drain_workqueue+0xca/0x1a0
>> [ 76.156182] destroy_workqueue+0x17/0x230
>> [ 76.156455] btrfs_destroy_workqueue+0x5d/0x1c0 [btrfs]
>> [ 76.156756] scrub_workers_put+0x2e/0x60 [btrfs]
>> [ 76.156931] btrfs_scrub_dev+0x329/0x5d0 [btrfs]
>> [ 76.157219] btrfs_ioctl+0x1ac3/0x2d80 [btrfs]
>> [ 76.157491] do_vfs_ioctl+0xa9/0x6d0
>> [ 76.157742] ksys_ioctl+0x60/0x90
>> [ 76.157910] __x64_sys_ioctl+0x16/0x20
>> [ 76.158177] do_syscall_64+0x50/0x180
>> [ 76.158429] entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> [ 76.158716]
>> other info that might help us debug this:
>>
>> [ 76.158908] Chain exists of:
>> (wq_completion)"%s-%s""btrfs", name --> &fs_devs->device_list_mutex
>> --> &fs_info->scrub_lock
>>
>> [ 76.159629] Possible unsafe locking scenario:
>>
>> [ 76.160607] CPU0 CPU1
>> [ 76.160934] ---- ----
>> [ 76.161210] lock(&fs_info->scrub_lock);
>> [ 76.161458]
>> lock(&fs_devs->device_list_mutex);
>> [ 76.161805]
>> lock(&fs_info->scrub_lock);
>> [ 76.161909] lock((wq_completion)"%s-%s""btrfs", name);
>> [ 76.162201]
>> *** DEADLOCK ***
>
> Please next time make sure the log messages are copied without
> whitespace damage. In many cases it's easy to glue the lines together,
> but specially the above locking scenario needs to be exact as the
> indentaion matters.
>
> I'll replace the whole report with the one in my logs as it does not
> have the device_list_mutex in the locking chain. This would be confusing
> as the problem with device_list_mutex was fixed already.
ok. Thanks.
-Anand
>>
>> [ 76.162627] 2 locks held by btrfs/4065:
>> [ 76.162897] #0: 00000000bef2775b (sb_writers#12){.+.+}, at:
>> mnt_want_write_file+0x24/0x50
>> [ 76.163335] #1: 0000000062392ab7 (&fs_info->scrub_lock){+.+.}, at:
>> btrfs_scrub_dev+0x316/0x5d0 [btrfs]
>> [ 76.163796]
>> stack backtrace:
>> [ 76.163911] CPU: 1 PID: 4065 Comm: btrfs Not tainted 4.20.0-rc3+ #41
>> [ 76.164228] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS
>> VirtualBox 12/01/2006
>> [ 76.164646] Call Trace:
>> [ 76.164872] dump_stack+0x5e/0x8b
>> [ 76.165128] print_circular_bug.isra.37+0x1f1/0x1fe
>> [ 76.165398] __lock_acquire+0x14aa/0x1620
>> [ 76.165652] lock_acquire+0xb0/0x190
>> [ 76.165910] ? flush_workqueue+0x70/0x4d0
>> [ 76.166175] flush_workqueue+0x9a/0x4d0
>> [ 76.166420] ? flush_workqueue+0x70/0x4d0
>> [ 76.166671] ? drain_workqueue+0x52/0x1a0
>> [ 76.166911] drain_workqueue+0xca/0x1a0
>> [ 76.167167] destroy_workqueue+0x17/0x230
>> [ 76.167428] btrfs_destroy_workqueue+0x5d/0x1c0 [btrfs]
>> [ 76.167720] scrub_workers_put+0x2e/0x60 [btrfs]
>> [ 76.168233] btrfs_scrub_dev+0x329/0x5d0 [btrfs]
>> [ 76.168504] ? __sb_start_write+0x121/0x1b0
>> [ 76.168759] ? mnt_want_write_file+0x24/0x50
>> [ 76.169654] btrfs_ioctl+0x1ac3/0x2d80 [btrfs]
>> [ 76.169934] ? find_held_lock+0x2d/0x90
>> [ 76.170204] ? find_held_lock+0x2d/0x90
>> [ 76.170450] do_vfs_ioctl+0xa9/0x6d0
>> [ 76.170690] ? __fget+0x101/0x1f0
>> [ 76.170910] ? __fget+0x5/0x1f0
>> [ 76.171157] ksys_ioctl+0x60/0x90
>> [ 76.171391] __x64_sys_ioctl+0x16/0x20
>> [ 76.171634] do_syscall_64+0x50/0x180
>> [ 76.171892] entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> [ 76.172186] RIP: 0033:0x7f61d422e567
>> [ 76.172425] Code: 44 00 00 48 8b 05 29 09 2d 00 64 c7 00 26 00 00 00
>> 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 b8 10 00 00 00 0f
>> 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d f9 08 2d 00 f7 d8 64 89 01 48
>
> This like can be ommitted from the log unless we really want to decode
> the instructions.
>
next prev parent reply other threads:[~2019-02-13 16:02 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-30 6:44 [PATCH v4 0/3] btrfs: scrub: fix scrub_lock Anand Jain
2019-01-30 6:45 ` [PATCH v4 1/3] btrfs: scrub: fix circular locking dependency warning Anand Jain
2019-01-30 14:07 ` David Sterba
2019-01-31 6:34 ` Anand Jain
2019-02-12 15:49 ` David Sterba
2019-02-12 16:45 ` David Sterba
2019-02-13 16:02 ` Anand Jain [this message]
2019-01-30 6:45 ` [PATCH v4 2/3] btrfs: scrub: add scrub_lock lockdep check in scrub_workers_get Anand Jain
2019-01-30 6:45 ` [PATCH v4 3/3] btrfs: scrub: convert scrub_workers_refcnt to refcount_t Anand Jain
2019-02-08 17:02 ` [PATCH v4 0/3] btrfs: scrub: fix scrub_lock David Sterba
2019-02-11 8:09 ` Anand Jain
2019-02-11 8:38 ` [PATCH v5 3/3] btrfs: scrub: convert scrub_workers_refcnt to refcount_t Anand Jain
2019-02-12 17:15 ` [PATCH] btrfs: scrub: add assertions for worker pointers David Sterba
2019-02-13 16:02 ` Anand Jain
2019-02-13 17:35 ` [PATCH v4 0/3] btrfs: scrub: fix scrub_lock David Sterba
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