From: Josef Bacik <josef@toxicpanda.com>
To: linux-btrfs@vger.kernel.org, kernel-team@fb.com
Subject: [PATCH v2 5/7] btrfs: delay blkdev_put until after the device remove
Date: Tue, 27 Jul 2021 17:01:17 -0400 [thread overview]
Message-ID: <e6af22a1b116e908d26359b55c0d6e2d50fe3105.1627419595.git.josef@toxicpanda.com> (raw)
In-Reply-To: <cover.1627419595.git.josef@toxicpanda.com>
When removing the device we call blkdev_put() on the device once we've
removed it, and because we have an EXCL open we need to take the
->open_mutex on the block device to clean it up. Unfortunately during
device remove we are holding the sb writers lock, which results in the
following lockdep splat
======================================================
WARNING: possible circular locking dependency detected
5.14.0-rc2+ #407 Not tainted
------------------------------------------------------
losetup/11595 is trying to acquire lock:
ffff973ac35dd138 ((wq_completion)loop0){+.+.}-{0:0}, at: flush_workqueue+0x67/0x5e0
but task is already holding lock:
ffff973ac9812c68 (&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_put+0x3a/0x220
btrfs_rm_device.cold+0x62/0xe5
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/11595:
#0: ffff973ac9812c68 (&lo->lo_mutex){+.+.}-{3:3}, at: __loop_clr_fd+0x41/0x660 [loop]
stack backtrace:
CPU: 0 PID: 11595 Comm: losetup Not tainted 5.14.0-rc2+ #407
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
RIP: 0033:0x7fc21255d4cb
So instead save the bdev and do the put once we've dropped the sb
writers lock in order to avoid the lockdep recursion.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
fs/btrfs/ioctl.c | 17 ++++++++++++++---
fs/btrfs/volumes.c | 19 +++++++++++++++----
fs/btrfs/volumes.h | 3 ++-
3 files changed, 31 insertions(+), 8 deletions(-)
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 0ba98e08a029..fabbfdfa56f5 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3205,6 +3205,8 @@ static long btrfs_ioctl_rm_dev_v2(struct file *file, void __user *arg)
struct inode *inode = file_inode(file);
struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
struct btrfs_ioctl_vol_args_v2 *vol_args;
+ struct block_device *bdev = NULL;
+ fmode_t mode;
int ret;
bool cancel = false;
@@ -3237,9 +3239,11 @@ static long btrfs_ioctl_rm_dev_v2(struct file *file, void __user *arg)
/* Exclusive operation is now claimed */
if (vol_args->flags & BTRFS_DEVICE_SPEC_BY_ID)
- ret = btrfs_rm_device(fs_info, NULL, vol_args->devid);
+ ret = btrfs_rm_device(fs_info, NULL, vol_args->devid, &bdev,
+ &mode);
else
- ret = btrfs_rm_device(fs_info, vol_args->name, 0);
+ ret = btrfs_rm_device(fs_info, vol_args->name, 0, &bdev,
+ &mode);
btrfs_exclop_finish(fs_info);
@@ -3255,6 +3259,8 @@ static long btrfs_ioctl_rm_dev_v2(struct file *file, void __user *arg)
kfree(vol_args);
err_drop:
mnt_drop_write_file(file);
+ if (bdev)
+ blkdev_put(bdev, mode);
return ret;
}
@@ -3263,6 +3269,8 @@ static long btrfs_ioctl_rm_dev(struct file *file, void __user *arg)
struct inode *inode = file_inode(file);
struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
struct btrfs_ioctl_vol_args *vol_args;
+ struct block_device *bdev = NULL;
+ fmode_t mode;
int ret;
bool cancel;
@@ -3284,7 +3292,8 @@ static long btrfs_ioctl_rm_dev(struct file *file, void __user *arg)
ret = exclop_start_or_cancel_reloc(fs_info, BTRFS_EXCLOP_DEV_REMOVE,
cancel);
if (ret == 0) {
- ret = btrfs_rm_device(fs_info, vol_args->name, 0);
+ ret = btrfs_rm_device(fs_info, vol_args->name, 0, &bdev,
+ &mode);
if (!ret)
btrfs_info(fs_info, "disk deleted %s", vol_args->name);
btrfs_exclop_finish(fs_info);
@@ -3294,6 +3303,8 @@ static long btrfs_ioctl_rm_dev(struct file *file, void __user *arg)
out_drop_write:
mnt_drop_write_file(file);
+ if (bdev)
+ blkdev_put(bdev, mode);
return ret;
}
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 3ab6c78e6eb2..f622e93a6ff1 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2076,7 +2076,7 @@ void btrfs_scratch_superblocks(struct btrfs_fs_info *fs_info,
}
int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path,
- u64 devid)
+ u64 devid, struct block_device **bdev, fmode_t *mode)
{
struct btrfs_device *device;
struct btrfs_fs_devices *cur_devices;
@@ -2186,15 +2186,26 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path,
mutex_unlock(&fs_devices->device_list_mutex);
/*
- * at this point, the device is zero sized and detached from
+ * At this point, the device is zero sized and detached from
* the devices list. All that's left is to zero out the old
* supers and free the device.
+ *
+ * We cannot call btrfs_close_bdev() here because we're holding the sb
+ * write lock, and blkdev_put() will pull in the ->open_mutex on the
+ * block device and it's dependencies. Instead just flush the device
+ * and let the caller do the final blkdev_put.
*/
- if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state))
+ if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) {
btrfs_scratch_superblocks(fs_info, device->bdev,
device->name->str);
+ if (device->bdev) {
+ sync_blockdev(device->bdev);
+ invalidate_bdev(device->bdev);
+ }
+ }
- btrfs_close_bdev(device);
+ *bdev = device->bdev;
+ *mode = device->mode;
synchronize_rcu();
btrfs_free_device(device);
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 70c749eee3ad..cc70e54cb901 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -472,7 +472,8 @@ struct btrfs_device *btrfs_alloc_device(struct btrfs_fs_info *fs_info,
const u8 *uuid);
void btrfs_free_device(struct btrfs_device *device);
int btrfs_rm_device(struct btrfs_fs_info *fs_info,
- const char *device_path, u64 devid);
+ const char *device_path, u64 devid,
+ struct block_device **bdev, fmode_t *mode);
void __exit btrfs_cleanup_fs_uuids(void);
int btrfs_num_copies(struct btrfs_fs_info *fs_info, u64 logical, u64 len);
int btrfs_grow_device(struct btrfs_trans_handle *trans,
--
2.26.3
next prev parent reply other threads:[~2021-07-27 21:03 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
2021-07-27 21:01 ` Josef Bacik [this message]
2021-08-25 1:00 ` [PATCH v2 5/7] btrfs: delay blkdev_put until after the device remove 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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