syzbot
possible deadlock in submit_bio_noacct_nocheck (2)
Status:
upstream: reported on 2026/08/16 23:17
Subsystems:
block
Labels:
prio:low
[Documentation on labels]
Reported-by: syzbot+ab02331ccbc7523c65ab@syzkaller.appspotmail.com
First crash: 7d07h, last: 6d16h
Sample crash report:
loop7: detected capacity change from 0 to 8192
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G L
------------------------------------------------------
syz.7.6727/29554 is trying to acquire lock:
ffff888026c5f020 (&q->q_usage_counter(io)#24){++++}-{0:0}, at: __submit_bio_noacct_mq block/blk-core.c:756 [inline]
ffff888026c5f020 (&q->q_usage_counter(io)#24){++++}-{0:0}, at: submit_bio_noacct_nocheck+0x2f4/0xa40 block/blk-core.c:790
but task is already holding lock:
ffff88805b4b80a8 (&sbi->fat_lock){+.+.}-{4:4}, at: lock_fat fs/fat/fatent.c:285 [inline]
ffff88805b4b80a8 (&sbi->fat_lock){+.+.}-{4:4}, at: fat_alloc_clusters+0x1f2/0xe30 fs/fat/fatent.c:482
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (&sbi->fat_lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
lock_fat fs/fat/fatent.c:285 [inline]
fat_count_free_clusters+0x157/0xb40 fs/fat/fatent.c:729
fat_statfs+0x135/0x400 fs/fat/inode.c:874
statfs_by_dentry fs/statfs.c:66 [inline]
vfs_statfs+0x147/0x2d0 fs/statfs.c:90
loop_get_discard_config drivers/block/loop.c:774 [inline]
loop_update_limits+0x375/0x920 drivers/block/loop.c:984
loop_configure+0x7d2/0xdc0 drivers/block/loop.c:1084
lo_ioctl+0xad5/0x2150 drivers/block/loop.c:1564
blkdev_ioctl+0x5e3/0x740 block/ioctl.c:798
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #1 (&q->limits_lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
queue_limits_start_update include/linux/blkdev.h:1101 [inline]
loop_set_dio drivers/block/loop.c:1460 [inline]
lo_simple_ioctl drivers/block/loop.c:1528 [inline]
lo_ioctl+0x16ca/0x2150 drivers/block/loop.c:1594
blkdev_ioctl+0x5e3/0x740 block/ioctl.c:798
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #0 (&q->q_usage_counter(io)#24){++++}-{0:0}:
check_prev_add kernel/locking/lockdep.c:3181 [inline]
check_prevs_add kernel/locking/lockdep.c:3300 [inline]
validate_chain kernel/locking/lockdep.c:3924 [inline]
__lock_acquire+0x15ff/0x2e50 kernel/locking/lockdep.c:5254
lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5908
bio_queue_enter block/blk.h:95 [inline]
blk_mq_submit_bio+0x7f8/0x2a70 block/blk-mq.c:3127
__submit_bio_noacct_mq block/blk-core.c:756 [inline]
submit_bio_noacct_nocheck+0x2f4/0xa40 block/blk-core.c:790
bh_submit fs/buffer.c:1146 [inline]
__bread_slow fs/buffer.c:1157 [inline]
__bread_gfp+0x1e9/0x380 fs/buffer.c:1403
sb_bread include/linux/buffer_head.h:344 [inline]
fat12_ent_bread+0x156/0x570 fs/fat/fatent.c:77
fat_ent_read_block+0x391/0x4b0 fs/fat/fatent.c:450
fat_alloc_clusters+0x434/0xe30 fs/fat/fatent.c:498
fat_alloc_new_dir+0x160/0xb90 fs/fat/dir.c:1184
vfat_mkdir+0x13a/0x300 fs/fat/namei_vfat.c:861
vfs_mkdir+0x40c/0x620 fs/namei.c:5410
filename_mkdirat+0x285/0x510 fs/namei.c:5443
__do_sys_mkdirat fs/namei.c:5464 [inline]
__se_sys_mkdirat+0x35/0x150 fs/namei.c:5461
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
other info that might help us debug this:
Chain exists of:
&q->q_usage_counter(io)#24 --> &q->limits_lock --> &sbi->fat_lock
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&sbi->fat_lock);
lock(&q->limits_lock);
lock(&sbi->fat_lock);
rlock(&q->q_usage_counter(io)#24);
*** DEADLOCK ***
locks held by syz.7.6727/29554: 4, last CPU#0:
#0: ffff8880357fc460 (sb_writers#17){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:494
#1: ffff88806a592260 (&sb->s_type->i_mutex_key#32/1){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:1069 [inline]
#1: ffff88806a592260 (&sb->s_type->i_mutex_key#32/1){+.+.}-{4:4}, at: __start_dirop fs/namei.c:2918 [inline]
#1: ffff88806a592260 (&sb->s_type->i_mutex_key#32/1){+.+.}-{4:4}, at: start_dirop fs/namei.c:2942 [inline]
#1: ffff88806a592260 (&sb->s_type->i_mutex_key#32/1){+.+.}-{4:4}, at: filename_create+0x200/0x370 fs/namei.c:5092
#2: ffff88805b4b81b8 (&sbi->s_lock){+.+.}-{4:4}, at: vfat_mkdir+0x10f/0x300 fs/fat/namei_vfat.c:858
#3: ffff88805b4b80a8 (&sbi->fat_lock){+.+.}-{4:4}, at: lock_fat fs/fat/fatent.c:285 [inline]
#3: ffff88805b4b80a8 (&sbi->fat_lock){+.+.}-{4:4}, at: fat_alloc_clusters+0x1f2/0xe30 fs/fat/fatent.c:482
stack backtrace:
CPU: 0 UID: 0 PID: 29554 Comm: syz.7.6727 Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2059
check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2191
check_prev_add kernel/locking/lockdep.c:3181 [inline]
check_prevs_add kernel/locking/lockdep.c:3300 [inline]
validate_chain kernel/locking/lockdep.c:3924 [inline]
__lock_acquire+0x15ff/0x2e50 kernel/locking/lockdep.c:5254
lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5908
bio_queue_enter block/blk.h:95 [inline]
blk_mq_submit_bio+0x7f8/0x2a70 block/blk-mq.c:3127
__submit_bio_noacct_mq block/blk-core.c:756 [inline]
submit_bio_noacct_nocheck+0x2f4/0xa40 block/blk-core.c:790
bh_submit fs/buffer.c:1146 [inline]
__bread_slow fs/buffer.c:1157 [inline]
__bread_gfp+0x1e9/0x380 fs/buffer.c:1403
sb_bread include/linux/buffer_head.h:344 [inline]
fat12_ent_bread+0x156/0x570 fs/fat/fatent.c:77
fat_ent_read_block+0x391/0x4b0 fs/fat/fatent.c:450
fat_alloc_clusters+0x434/0xe30 fs/fat/fatent.c:498
fat_alloc_new_dir+0x160/0xb90 fs/fat/dir.c:1184
vfat_mkdir+0x13a/0x300 fs/fat/namei_vfat.c:861
vfs_mkdir+0x40c/0x620 fs/namei.c:5410
filename_mkdirat+0x285/0x510 fs/namei.c:5443
__do_sys_mkdirat fs/namei.c:5464 [inline]
__se_sys_mkdirat+0x35/0x150 fs/namei.c:5461
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f165a19cf47
Code: 00 66 90 48 89 f2 b9 00 01 00 00 48 89 fe bf 9c ff ff ff e9 db f7 ff ff 66 2e 0f 1f 84 00 00 00 00 00 90 b8 02 01 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f165b14be58 EFLAGS: 00000246 ORIG_RAX: 0000000000000102
RAX: ffffffffffffffda RBX: 00007f165b14bee0 RCX: 00007f165a19cf47
RDX: 00000000000001ff RSI: 0000200000000240 RDI: 00000000ffffff9c
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000200000000240
R13: 00007f165b14bea0 R14: 0000000000000000 R15: 0000000000000000
</TASK>
Struck through repros no longer work on HEAD.