syzbot

refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 14 at lib/refcount.c:28 refcount_warn_saturate+0x154/0x1f8 lib/refcount.c:28
Modules linked in:
CPU: 0 PID: 14 Comm: ksoftirqd/0 Not tainted 5.15.184-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : refcount_warn_saturate+0x154/0x1f8 lib/refcount.c:28
lr : refcount_warn_saturate+0x154/0x1f8 lib/refcount.c:28
sp : ffff80001b307b40
x29: ffff80001b307b40 x28: fffffbffefff2fc0 x27: 1fffe0001992b043
x26: 1fffe0001992b043
 x25: 0000000000000000
 x24: 0000000000000001

x23: dfff800000000000
 x22: fffffbffefff3088
 x21: 0000000000000000
x20: ffff0000cc9582e8 x19: ffff80001658e000 x18: 0000000000000101
x17: 0000000000000000 x16: ffff8000111a5644 x15: 0000000000000012
x14: 0000000000000000 x13: 1ffff0000282a06b x12: 0000000000ff0100
x11: 0000000000000100 x10: 0000000000000000 x9 : 9b237cd785ead200
x8 : 9b237cd785ead200
 x7 : 0000000000000000 x6 : 0000000000000000

x5 : 0000000000000080
 x4 : 0000000000000000 x3 : ffff80000850383c
x2 : 0000000000000001 x1 : 0000000000000100 x0 : 0000000000000026
Call trace:
 refcount_warn_saturate+0x154/0x1f8 lib/refcount.c:28
 __refcount_sub_and_test include/linux/refcount.h:283 [inline]
 __refcount_dec_and_test include/linux/refcount.h:315 [inline]
 refcount_dec_and_test include/linux/refcount.h:333 [inline]
 blk_mq_free_request+0x434/0x578 block/blk-mq.c:543
 __blk_mq_end_request+0x30c/0x344 block/blk-mq.c:568
 blk_mq_end_request+0x68/0x88 block/blk-mq.c:577
 nbd_complete_rq+0x48/0x160 drivers/block/nbd.c:360
 blk_complete_reqs block/blk-mq.c:587 [inline]
 blk_done_softirq+0x11c/0x168 block/blk-mq.c:592
 handle_softirqs+0x344/0xbf0 kernel/softirq.c:558
 run_ksoftirqd+0x7c/0x2a0 kernel/softirq.c:925
 smpboot_thread_fn+0x4b0/0x920 kernel/smpboot.c:164
 kthread+0x374/0x454 kernel/kthread.c:334
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:870
irq event stamp: 256683
hardirqs last  enabled at (256682): [<ffff8000111a3bac>] __exit_to_kernel_mode arch/arm64/kernel/entry-common.c:81 [inline]
hardirqs last  enabled at (256682): [<ffff8000111a3bac>] exit_to_kernel_mode+0xe0/0x168 arch/arm64/kernel/entry-common.c:91
hardirqs last disabled at (256683): [<ffff8000111a0f18>] el1_dbg+0x24/0x80 arch/arm64/kernel/entry-common.c:396
softirqs last  enabled at (256654): [<ffff80000819d0d8>] softirq_handle_end kernel/softirq.c:401 [inline]
softirqs last  enabled at (256654): [<ffff80000819d0d8>] handle_softirqs+0xa4c/0xbf0 kernel/softirq.c:586
softirqs last disabled at (256659): [<ffff80000819f98c>] run_ksoftirqd+0x7c/0x2a0 kernel/softirq.c:925
---[ end trace feb4dddeaa23838f ]---