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Subject[PATCH 5.15 087/230] btrfs: use btrfs_get_dev_args_from_path in dev removal ioctls
Date
From: Josef Bacik <josef@toxicpanda.com>

[ Upstream commit 1a15eb724aaef8656f8cc01d9355797cfe7c618e ]

For device removal and replace we call btrfs_find_device_by_devspec,
which if we give it a device path and nothing else will call
btrfs_get_dev_args_from_path, which opens the block device and reads the
super block and then looks up our device based on that.

However at this point we're holding the sb write "lock", so reading the
block device pulls in the dependency of ->open_mutex, which produces the
following lockdep splat

======================================================
WARNING: possible circular locking dependency detected
5.14.0-rc2+ #405 Not tainted
------------------------------------------------------
losetup/11576 is trying to acquire lock:
ffff9bbe8cded938 ((wq_completion)loop0){+.+.}-{0:0}, at: flush_workqueue+0x67/0x5e0

but task is already holding lock:
ffff9bbe88e4fc68 (&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_get_by_path+0x98/0xa0
btrfs_get_bdev_and_sb+0x1b/0xb0
btrfs_find_device_by_devspec+0x12b/0x1c0
btrfs_rm_device+0x127/0x610
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/11576:
#0: ffff9bbe88e4fc68 (&lo->lo_mutex){+.+.}-{3:3}, at: __loop_clr_fd+0x41/0x660 [loop]

stack backtrace:
CPU: 0 PID: 11576 Comm: losetup Not tainted 5.14.0-rc2+ #405
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: 0033:0x7f31b02404cb

Instead what we want to do is populate our device lookup args before we
grab any locks, and then pass these args into btrfs_rm_device(). From
there we can find the device and do the appropriate removal.

Suggested-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/btrfs/ioctl.c | 67 +++++++++++++++++++++++++++-------------------
fs/btrfs/volumes.c | 15 +++++------
fs/btrfs/volumes.h | 2 +-
3 files changed, 48 insertions(+), 36 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 4951a2ab88dd..4317720a29e8 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3218,6 +3218,7 @@ static long btrfs_ioctl_add_dev(struct btrfs_fs_info *fs_info, void __user *arg)

static long btrfs_ioctl_rm_dev_v2(struct file *file, void __user *arg)
{
+ BTRFS_DEV_LOOKUP_ARGS(args);
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;
@@ -3229,35 +3230,39 @@ static long btrfs_ioctl_rm_dev_v2(struct file *file, void __user *arg)
if (!capable(CAP_SYS_ADMIN))
return -EPERM;

- ret = mnt_want_write_file(file);
- if (ret)
- return ret;
-
vol_args = memdup_user(arg, sizeof(*vol_args));
if (IS_ERR(vol_args)) {
ret = PTR_ERR(vol_args);
- goto err_drop;
+ goto out;
}

if (vol_args->flags & ~BTRFS_DEVICE_REMOVE_ARGS_MASK) {
ret = -EOPNOTSUPP;
goto out;
}
+
vol_args->name[BTRFS_SUBVOL_NAME_MAX] = '\0';
- if (!(vol_args->flags & BTRFS_DEVICE_SPEC_BY_ID) &&
- strcmp("cancel", vol_args->name) == 0)
+ if (vol_args->flags & BTRFS_DEVICE_SPEC_BY_ID) {
+ args.devid = vol_args->devid;
+ } else if (!strcmp("cancel", vol_args->name)) {
cancel = true;
+ } else {
+ ret = btrfs_get_dev_args_from_path(fs_info, &args, vol_args->name);
+ if (ret)
+ goto out;
+ }
+
+ ret = mnt_want_write_file(file);
+ if (ret)
+ goto out;

ret = exclop_start_or_cancel_reloc(fs_info, BTRFS_EXCLOP_DEV_REMOVE,
cancel);
if (ret)
- goto out;
- /* Exclusive operation is now claimed */
+ goto err_drop;

- if (vol_args->flags & BTRFS_DEVICE_SPEC_BY_ID)
- ret = btrfs_rm_device(fs_info, NULL, vol_args->devid, &bdev, &mode);
- else
- ret = btrfs_rm_device(fs_info, vol_args->name, 0, &bdev, &mode);
+ /* Exclusive operation is now claimed */
+ ret = btrfs_rm_device(fs_info, &args, &bdev, &mode);

btrfs_exclop_finish(fs_info);

@@ -3269,17 +3274,19 @@ static long btrfs_ioctl_rm_dev_v2(struct file *file, void __user *arg)
btrfs_info(fs_info, "device deleted: %s",
vol_args->name);
}
-out:
- kfree(vol_args);
err_drop:
mnt_drop_write_file(file);
if (bdev)
blkdev_put(bdev, mode);
+out:
+ btrfs_put_dev_args_from_path(&args);
+ kfree(vol_args);
return ret;
}

static long btrfs_ioctl_rm_dev(struct file *file, void __user *arg)
{
+ BTRFS_DEV_LOOKUP_ARGS(args);
struct inode *inode = file_inode(file);
struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
struct btrfs_ioctl_vol_args *vol_args;
@@ -3291,32 +3298,38 @@ static long btrfs_ioctl_rm_dev(struct file *file, void __user *arg)
if (!capable(CAP_SYS_ADMIN))
return -EPERM;

- ret = mnt_want_write_file(file);
- if (ret)
- return ret;
-
vol_args = memdup_user(arg, sizeof(*vol_args));
- if (IS_ERR(vol_args)) {
- ret = PTR_ERR(vol_args);
- goto out_drop_write;
- }
+ if (IS_ERR(vol_args))
+ return PTR_ERR(vol_args);
+
vol_args->name[BTRFS_PATH_NAME_MAX] = '\0';
- cancel = (strcmp("cancel", vol_args->name) == 0);
+ if (!strcmp("cancel", vol_args->name)) {
+ cancel = true;
+ } else {
+ ret = btrfs_get_dev_args_from_path(fs_info, &args, vol_args->name);
+ if (ret)
+ goto out;
+ }
+
+ ret = mnt_want_write_file(file);
+ if (ret)
+ goto out;

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, &bdev, &mode);
+ ret = btrfs_rm_device(fs_info, &args, &bdev, &mode);
if (!ret)
btrfs_info(fs_info, "disk deleted %s", vol_args->name);
btrfs_exclop_finish(fs_info);
}

- kfree(vol_args);
-out_drop_write:
mnt_drop_write_file(file);
if (bdev)
blkdev_put(bdev, mode);
+out:
+ btrfs_put_dev_args_from_path(&args);
+ kfree(vol_args);
return ret;
}

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 8d09e6d442b2..3bd68f1b79e6 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2120,8 +2120,9 @@ void btrfs_scratch_superblocks(struct btrfs_fs_info *fs_info,
update_dev_time(device_path);
}

-int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path,
- u64 devid, struct block_device **bdev, fmode_t *mode)
+int btrfs_rm_device(struct btrfs_fs_info *fs_info,
+ struct btrfs_dev_lookup_args *args,
+ struct block_device **bdev, fmode_t *mode)
{
struct btrfs_device *device;
struct btrfs_fs_devices *cur_devices;
@@ -2140,14 +2141,12 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path,
if (ret)
goto out;

- device = btrfs_find_device_by_devspec(fs_info, devid, device_path);
-
- if (IS_ERR(device)) {
- if (PTR_ERR(device) == -ENOENT &&
- device_path && strcmp(device_path, "missing") == 0)
+ device = btrfs_find_device(fs_info->fs_devices, args);
+ if (!device) {
+ if (args->missing)
ret = BTRFS_ERROR_DEV_MISSING_NOT_FOUND;
else
- ret = PTR_ERR(device);
+ ret = -ENOENT;
goto out;
}

diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index d1df03f77e29..30288b728bbb 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -496,7 +496,7 @@ struct btrfs_device *btrfs_alloc_device(struct btrfs_fs_info *fs_info,
void btrfs_put_dev_args_from_path(struct btrfs_dev_lookup_args *args);
void btrfs_free_device(struct btrfs_device *device);
int btrfs_rm_device(struct btrfs_fs_info *fs_info,
- const char *device_path, u64 devid,
+ struct btrfs_dev_lookup_args *args,
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);
--
2.35.1


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