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: 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