syzbot has found a reproducer for the following issue on: HEAD commit: 729e3d09 Merge tag 'ceph-for-5.9-rc5' of git://github.com/.. git tree: upstream console output: https://syzkaller.appspot.com/x/log.txt?x=12f2ce0d900000 kernel config: https://syzkaller.appspot.com/x/.config?x=c61610091f4ca8c4 dashboard link: https://syzkaller.appspot.com/bug?extid=956ef5eac18eadd0fb7f compiler: gcc (GCC) 10.1.0-syz 20200507 syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10f3a853900000 C reproducer: https://syzkaller.appspot.com/x/repro.c?x=157f7263900000 IMPORTANT: if you fix the issue, please add the following tag to the commit: Reported-by: syzbot+956ef5eac18eadd0fb7f@xxxxxxxxxxxxxxxxxxxxxxxxx ------------[ cut here ]------------ refcount_t: underflow; use-after-free. WARNING: CPU: 0 PID: 7382 at lib/refcount.c:28 refcount_warn_saturate+0x1d1/0x1e0 lib/refcount.c:28 Kernel panic - not syncing: panic_on_warn set ... CPU: 0 PID: 7382 Comm: io_wqe_worker-1 Not tainted 5.9.0-rc4-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x198/0x1fd lib/dump_stack.c:118 panic+0x347/0x7c0 kernel/panic.c:231 __warn.cold+0x20/0x46 kernel/panic.c:600 report_bug+0x1bd/0x210 lib/bug.c:198 handle_bug+0x38/0x90 arch/x86/kernel/traps.c:234 exc_invalid_op+0x14/0x40 arch/x86/kernel/traps.c:254 asm_exc_invalid_op+0x12/0x20 arch/x86/include/asm/idtentry.h:536 RIP: 0010:refcount_warn_saturate+0x1d1/0x1e0 lib/refcount.c:28 Code: e9 db fe ff ff 48 89 df e8 2c dd 18 fe e9 8a fe ff ff e8 c2 d6 d8 fd 48 c7 c7 60 dc 93 88 c6 05 0d 0d 12 07 01 e8 b1 d7 a9 fd <0f> 0b e9 af fe ff ff 0f 1f 84 00 00 00 00 00 41 56 41 55 41 54 55 RSP: 0018:ffffc9000810fe08 EFLAGS: 00010286 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: ffff88809592a200 RSI: ffffffff815db9a7 RDI: fffff52001021fb3 RBP: 0000000000000003 R08: 0000000000000001 R09: ffff8880ae6318e7 R10: 0000000000000000 R11: 0000000000000000 R12: ffff88809a6080b8 R13: ffff8880a7896e30 R14: ffff8880a7896e00 R15: ffff8880a6727f00 refcount_sub_and_test include/linux/refcount.h:274 [inline] refcount_dec_and_test include/linux/refcount.h:294 [inline] io_worker_exit fs/io-wq.c:236 [inline] io_wqe_worker+0xcdb/0x10e0 fs/io-wq.c:596 kthread+0x3b5/0x4a0 kernel/kthread.c:292 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294 Kernel Offset: disabled Rebooting in 86400 seconds..
