From: David Sterba <dsterba@suse.cz>
To: Josef Bacik <josef@toxicpanda.com>
Cc: linux-btrfs@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH v2 4/7] btrfs: update the bdev time directly when closing
Date: Thu, 2 Sep 2021 14:16:09 +0200 [thread overview]
Message-ID: <20210902121608.GP3379@twin.jikos.cz> (raw)
In-Reply-To: <7a02499fac5a53031b333ce58d84089c8ce9e329.1627419595.git.josef@toxicpanda.com>
On Tue, Jul 27, 2021 at 05:01:16PM -0400, Josef Bacik wrote:
> We update the ctime/mtime of a block device when we remove it so that
> blkid knows the device changed. However we do this by re-opening the
> block device and calling filp_update_time. This is more correct because
> it'll call the inode->i_op->update_time if it exists, but the block dev
> inodes do not do this. Instead call generic_update_time() on the
> bd_inode in order to avoid the blkdev_open path and get rid of the
> following lockdep splat
>
> ======================================================
> WARNING: possible circular locking dependency detected
> 5.14.0-rc2+ #406 Not tainted
> ------------------------------------------------------
> losetup/11596 is trying to acquire lock:
> ffff939640d2f538 ((wq_completion)loop0){+.+.}-{0:0}, at: flush_workqueue+0x67/0x5e0
>
> but task is already holding lock:
> ffff939655510c68 (&lo->lo_mutex){+.+.}-{3:3}, at: __loop_clr_fd+0x41/0x660 [loop]
>
> which lock already depends on the new lock.
>
> the existing dependency chain (in reverse order) is:
>
> -> #4 (&lo->lo_mutex){+.+.}-{3:3}:
> __mutex_lock+0x7d/0x750
> lo_open+0x28/0x60 [loop]
> blkdev_get_whole+0x25/0xf0
> blkdev_get_by_dev.part.0+0x168/0x3c0
> blkdev_open+0xd2/0xe0
> do_dentry_open+0x161/0x390
> path_openat+0x3cc/0xa20
> do_filp_open+0x96/0x120
> do_sys_openat2+0x7b/0x130
> __x64_sys_openat+0x46/0x70
> do_syscall_64+0x38/0x90
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> -> #3 (&disk->open_mutex){+.+.}-{3:3}:
> __mutex_lock+0x7d/0x750
> blkdev_get_by_dev.part.0+0x56/0x3c0
> blkdev_open+0xd2/0xe0
> do_dentry_open+0x161/0x390
> path_openat+0x3cc/0xa20
> do_filp_open+0x96/0x120
> file_open_name+0xc7/0x170
> filp_open+0x2c/0x50
> btrfs_scratch_superblocks.part.0+0x10f/0x170
> btrfs_rm_device.cold+0xe8/0xed
> btrfs_ioctl+0x2a31/0x2e70
> __x64_sys_ioctl+0x80/0xb0
> do_syscall_64+0x38/0x90
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> -> #2 (sb_writers#12){.+.+}-{0:0}:
> lo_write_bvec+0xc2/0x240 [loop]
> loop_process_work+0x238/0xd00 [loop]
> process_one_work+0x26b/0x560
> worker_thread+0x55/0x3c0
> kthread+0x140/0x160
> ret_from_fork+0x1f/0x30
>
> -> #1 ((work_completion)(&lo->rootcg_work)){+.+.}-{0:0}:
> process_one_work+0x245/0x560
> worker_thread+0x55/0x3c0
> kthread+0x140/0x160
> ret_from_fork+0x1f/0x30
>
> -> #0 ((wq_completion)loop0){+.+.}-{0:0}:
> __lock_acquire+0x10ea/0x1d90
> lock_acquire+0xb5/0x2b0
> flush_workqueue+0x91/0x5e0
> drain_workqueue+0xa0/0x110
> destroy_workqueue+0x36/0x250
> __loop_clr_fd+0x9a/0x660 [loop]
> block_ioctl+0x3f/0x50
> __x64_sys_ioctl+0x80/0xb0
> do_syscall_64+0x38/0x90
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> other info that might help us debug this:
>
> Chain exists of:
> (wq_completion)loop0 --> &disk->open_mutex --> &lo->lo_mutex
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&lo->lo_mutex);
> lock(&disk->open_mutex);
> lock(&lo->lo_mutex);
> lock((wq_completion)loop0);
>
> *** DEADLOCK ***
>
> 1 lock held by losetup/11596:
> #0: ffff939655510c68 (&lo->lo_mutex){+.+.}-{3:3}, at: __loop_clr_fd+0x41/0x660 [loop]
>
> stack backtrace:
> CPU: 1 PID: 11596 Comm: losetup Not tainted 5.14.0-rc2+ #406
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-2.fc32 04/01/2014
> Call Trace:
> dump_stack_lvl+0x57/0x72
> check_noncircular+0xcf/0xf0
> ? stack_trace_save+0x3b/0x50
> __lock_acquire+0x10ea/0x1d90
> lock_acquire+0xb5/0x2b0
> ? flush_workqueue+0x67/0x5e0
> ? lockdep_init_map_type+0x47/0x220
> flush_workqueue+0x91/0x5e0
> ? flush_workqueue+0x67/0x5e0
> ? verify_cpu+0xf0/0x100
> drain_workqueue+0xa0/0x110
> destroy_workqueue+0x36/0x250
> __loop_clr_fd+0x9a/0x660 [loop]
> ? blkdev_ioctl+0x8d/0x2a0
> block_ioctl+0x3f/0x50
> __x64_sys_ioctl+0x80/0xb0
> do_syscall_64+0x38/0x90
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Added to misc-next, thanks.
next prev parent reply other threads:[~2021-09-02 12:16 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-27 21:01 [PATCH v2 0/7] Josef Bacik
2021-07-27 21:01 ` [PATCH v2 1/7] btrfs: do not call close_fs_devices in btrfs_rm_device Josef Bacik
2021-09-01 8:13 ` Anand Jain
2021-07-27 21:01 ` [PATCH v2 2/7] btrfs: do not take the uuid_mutex " Josef Bacik
2021-09-01 12:01 ` Anand Jain
2021-09-01 17:08 ` David Sterba
2021-09-01 17:10 ` Josef Bacik
2021-09-01 19:49 ` Anand Jain
2021-09-02 12:58 ` David Sterba
2021-09-02 14:10 ` Josef Bacik
2021-09-17 14:33 ` David Sterba
2021-09-20 7:45 ` Anand Jain
2021-09-20 8:26 ` David Sterba
2021-09-20 9:41 ` Anand Jain
2021-09-23 4:33 ` Anand Jain
2021-09-21 11:59 ` Filipe Manana
2021-09-21 12:17 ` Filipe Manana
2021-09-22 15:33 ` Filipe Manana
2021-09-23 4:15 ` Anand Jain
2021-09-23 3:58 ` [PATCH] btrfs: drop lockdep assert in close_fs_devices() Anand Jain
2021-09-23 4:04 ` Anand Jain
2021-07-27 21:01 ` [PATCH v2 3/7] btrfs: do not read super look for a device path Josef Bacik
2021-08-25 2:00 ` Anand Jain
2021-09-27 15:32 ` Josef Bacik
2021-09-28 11:50 ` Anand Jain
2021-07-27 21:01 ` [PATCH v2 4/7] btrfs: update the bdev time directly when closing Josef Bacik
2021-08-25 0:35 ` Anand Jain
2021-09-02 12:16 ` David Sterba [this message]
2021-07-27 21:01 ` [PATCH v2 5/7] btrfs: delay blkdev_put until after the device remove Josef Bacik
2021-08-25 1:00 ` Anand Jain
2021-09-02 12:16 ` David Sterba
2021-07-27 21:01 ` [PATCH v2 6/7] btrfs: unify common code for the v1 and v2 versions of " Josef Bacik
2021-08-25 1:19 ` Anand Jain
2021-09-01 14:05 ` Nikolay Borisov
2021-07-27 21:01 ` [PATCH v2 7/7] btrfs: do not take the device_list_mutex in clone_fs_devices Josef Bacik
2021-08-24 22:08 ` Anand Jain
2021-09-01 13:35 ` Nikolay Borisov
2021-09-02 12:59 ` David Sterba
2021-09-17 15:06 ` [PATCH v2 0/7] David Sterba
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