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[BUG]
There is a lockdep report related to device scan:
======================================================
WARNING: possible circular locking dependency detected
7.2.0-20260712.rc2.git0.e3321fa3034d.300.fc44.s390x+debug #1 Not tainted
------------------------------------------------------
(udev-worker)/1653 is trying to acquire lock:
0000006919232220 (&type->i_mutex_dir_key#2){++++}-{3:3}, at: lookup_slow+0x3e/0x70
but task is already holding lock:
00000069238564d8 (&fs_devs->device_list_mutex){+.+.}-{3:3}, at: device_list_add.constprop.0+0x148/0xc60
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #5 (&fs_devs->device_list_mutex){+.+.}-{3:3}:
lock_acquire+0x150/0x3f0
__mutex_lock+0xba/0xdc0
mutex_lock_nested+0x32/0x40
write_all_supers+0x7a/0x670
btrfs_sync_log+0xae6/0xdd0
btrfs_sync_file+0x4fa/0x7a0
__s390x_sys_fsync+0x52/0xa0
__do_syscall+0x172/0x750
system_call+0x72/0x90
-> #4 (&fs_info->tree_log_mutex){+.+.}-{3:3}:
lock_acquire+0x150/0x3f0
__mutex_lock+0xba/0xdc0
mutex_lock_nested+0x32/0x40
btrfs_sync_log+0xaba/0xdd0
btrfs_sync_file+0x4fa/0x7a0
__s390x_sys_fsync+0x52/0xa0
__do_syscall+0x172/0x750
system_call+0x72/0x90
-> #3 (btrfs_trans_num_extwriters){.+.+}-{0:0}:
lock_acquire+0x150/0x3f0
join_transaction+0x108/0x680
start_transaction+0x21a/0x660
btrfs_join_transaction+0x32/0x40
btrfs_dirty_inode+0x52/0xf0
touch_atime+0x90/0xc0
filemap_read+0x446/0x450
vfs_read+0x208/0x370
ksys_read+0x88/0x120
__do_syscall+0x172/0x750
system_call+0x72/0x90
-> #2 (btrfs_trans_num_writers){.+.+}-{0:0}:
reacquire_held_locks+0x14c/0x240
__lock_release.isra.0+0xd8/0x380
lock_release+0xf6/0x270
percpu_up_read+0x28/0xf0
__btrfs_end_transaction+0x178/0x1f0
btrfs_dirty_inode+0x82/0xf0
touch_atime+0x90/0xc0
btrfs_file_mmap_prepare+0x8c/0xa0
__mmap_region+0x214/0x780
mmap_region+0x108/0x160
do_mmap+0x402/0x5a0
vm_mmap_pgoff+0x156/0x230
ksys_mmap_pgoff+0x17e/0x220
__s390x_sys_old_mmap+0xa8/0x140
__do_syscall+0x172/0x750
system_call+0x72/0x90
-> #1 (&mm->mmap_lock){++++}-{3:3}:
lock_acquire+0x150/0x3f0
__might_fault+0x7a/0xa0
filldir64+0x11c/0x210
offset_readdir+0x92/0x200
iterate_dir+0xcc/0x2d0
__do_sys_getdents64+0x7a/0x130
__do_syscall+0x172/0x750
system_call+0x72/0x90
-> #0 (&type->i_mutex_dir_key#2){++++}-{3:3}:
check_prev_add+0x160/0xf40
__lock_acquire+0x12aa/0x15a0
lock_acquire+0x150/0x3f0
down_read+0x5a/0x280
lookup_slow+0x3e/0x70
path_lookupat+0x1f0/0x370
filename_lookup+0xce/0x1f0
kern_path+0x48/0x70
is_same_device+0x146/0x300
device_list_add.constprop.0+0x1be/0xc60
btrfs_scan_one_device+0x13a/0x2f0
btrfs_control_ioctl+0x110/0x1e0
__s390x_sys_ioctl+0xfa/0x130
__do_syscall+0x172/0x750
system_call+0x72/0x90
other info that might help us debug this:
Chain exists of:
&type->i_mutex_dir_key#2 --> &fs_info->tree_log_mutex --> &fs_devs->device_list_mutex
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&fs_devs->device_list_mutex);
lock(&fs_info->tree_log_mutex);
lock(&fs_devs->device_list_mutex);
rlock(&type->i_mutex_dir_key#2);
*** DEADLOCK ***
2 locks held by (udev-worker)/1653:
#0: 0000016c727051c8 (uuid_mutex){+.+.}-{3:3}, at: btrfs_control_ioctl+0x102/0x1e0
#1: 00000069238564d8 (&fs_devs->device_list_mutex){+.+.}-{3:3}, at: device_list_add.constprop.0+0x148/0xc60
stack backtrace:
CPU: 2 UID: 0 PID: 1653 Comm: (udev-worker) Not tainted 7.2.0-20260712.rc2.git0.e3321fa3034d.300.fc44.s390x+debug #1 PREEMPT
Hardware name: IBM 3931 A01 701 (LPAR)
Call Trace:
[<0000016c70680e3e>] dump_stack_lvl+0xae/0x108
[<0000016c7078aa44>] print_circular_bug+0x1a4/0x230
[<0000016c7078ac5c>] check_noncircular+0x18c/0x1b0
[<0000016c7078c030>] check_prev_add+0x160/0xf40
[<0000016c7078fbaa>] __lock_acquire+0x12aa/0x15a0
[<0000016c7078fff0>] lock_acquire+0x150/0x3f0
[<0000016c7180e2fa>] down_read+0x5a/0x280
[<0000016c70b88dde>] lookup_slow+0x3e/0x70
[<0000016c70b8f5d0>] path_lookupat+0x1f0/0x370
[<0000016c70b900ae>] filename_lookup+0xce/0x1f0
[<0000016c70b90218>] kern_path+0x48/0x70
[<0000016c70f5b4a6>] is_same_device+0x146/0x300
[<0000016c70f67cfe>] device_list_add.constprop.0+0x1be/0xc60
[<0000016c70f688da>] btrfs_scan_one_device+0x13a/0x2f0
[<0000016c70ed9cb0>] btrfs_control_ioctl+0x110/0x1e0
[<0000016c70b97d0a>] __s390x_sys_ioctl+0xfa/0x130
[<0000016c718004d2>] __do_syscall+0x172/0x750
[<0000016c718155d2>] system_call+0x72/0x90
[CAUSE]
Btrfs device scan will call is_same_device() with device_list_mutex
held. But is_same_device() will call kern_path() which will do path
resolution and lock the inode.
So device scan has the following lock sequence:
mutex_lock(device_list_mutex) from device_list_add()
|
v
inode_lock_shared() from lookup_slow() during kern_path().
Meanwhile another thread is fsyncing, which has the following
lock sequence:
inode_lock() from btrfs_inode_lock() inside btrfs_direct_write()
|
v
mutex_lock(tree_log_mutex() from btrfs_sync_log(), which is further
triggered from
iomap_dio_complete()->generic_write_sync()->btrfs_sync_file().
|
v
mutex_lock(device_list_mutex) from write_all_supers() inside
btrfs_sync_log().
So the device scan has a reversed lock sequence, compared to the fsync
one, this means we can have the following deadlock:
Device scan | Fsync
----------------------------------------+--------------------------------
device_list_mutex locked |
| inode locked
| try to lock device_list_mutex
try to lock inode |
[FIX]
Instead of a full path lookup, use dev_t to determine if two device
paths are pointing to the same block device.
Inside kernel dev_t is going to uniquely determine a block device, and
the device path lookup is already done by lookup_bdev(), which is done
without device_list_mutex held, thus no reversed locking sequence.
Reported-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Link: https://lore.kernel.org/linux-btrfs/5a9d9847-4ae6-43c4-afdc-6e5fa51d6117@linux.ibm.com/
Fixes:
|
History
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