[PATCH AUTOSEL 5.14 17/25] btrfs: delay blkdev_put until after the device remove
From: Sasha Levin
Date: Mon Sep 13 2021 - 18:35:34 EST
From: Josef Bacik <josef@xxxxxxxxxxxxxx>
[ Upstream commit 3fa421dedbc82f985f030c5a6480ea2d784334c3 ]
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.
Reviewed-by: Anand Jain <anand.jain@xxxxxxxxxx>
Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
fs/btrfs/ioctl.c | 15 +++++++++++----
fs/btrfs/volumes.c | 23 +++++++++++++++++------
fs/btrfs/volumes.h | 3 ++-
3 files changed, 30 insertions(+), 11 deletions(-)
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 0ba98e08a029..50e12989e84a 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 +3239,9 @@ 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 +3257,8 @@ 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 +3267,8 @@ 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 +3290,7 @@ 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);
@@ -3293,7 +3299,8 @@ static long btrfs_ioctl_rm_dev(struct file *file, void __user *arg)
kfree(vol_args);
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 8dc14985128f..7f38f81f1a92 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2119,7 +2119,7 @@ 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;
@@ -2233,15 +2233,26 @@ 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
- * the devices list. All that's left is to zero out the old
- * supers and free the device.
+ * 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 55a8ba244716..f77f869dfd2c 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,
--
2.30.2