Hi everyone. I have recently switched to a setup running QEMU 5.0(which supports io_uring) for a Windows 10 guest on Linux v5.4.63. The QEMU hosts /dev/nvme0n1p3 to the guest with virtio-blk with discard/unmap enabled. I've been having a weird issue where the system would randomly hang whenever I turn on or shutdown the guest. The host will stay up for a bit and then just hang. No response on SSH, etc. Even ping doesn't work. It's been hard to even get a log to debug the issue, but I've been able to get a show-backtrace-all-active-cpus sysrq dmesg on the most recent encounter with the issue and it's showing some io_uring functions. Since I've been encountering the issue ever since I switched to QEMU 5.0, I suspect io_uring may be the culprit to the issue. While I'd love to try out the mainline kernel, it's currently not feasible at the moment as I have to stay in linux-5.4.y. Backporting mainline's io_uring also seems to be a non-trivial job. Any tips would be appreciated. I can build my own kernel and I'm willing to try out (backported) patches. Thanks. [243683.539303] NMI backtrace for cpu 1 [243683.539303] CPU: 1 PID: 1527 Comm: qemu-system-x86 Tainted: P W O 5.4.63+ #1 [243683.539303] Hardware name: System manufacturer System Product Name/PRIME Z370-A, BIOS 2401 07/12/2019 [243683.539304] RIP: 0010:io_uring_flush+0x98/0x140 [243683.539304] Code: e4 74 70 48 8b 93 e8 02 00 00 48 8b 32 48 8b 4a 08 48 89 4e 08 48 89 31 48 89 12 48 89 52 08 48 8b 72 f8 81 4a a8 00 40 00 00 <48> 85 f6 74 15 4c 3b 62 c8 75 0f ba 01 00 00 00 bf 02 00 00 00 e8 [243683.539304] RSP: 0018:ffff8881f20c3e28 EFLAGS: 00000006 [243683.539305] RAX: ffff888419cd94e0 RBX: ffff88842ba49800 RCX: ffff888419cd94e0 [243683.539305] RDX: ffff888419cd94e0 RSI: ffff888419cd94d0 RDI: ffff88842ba49af8 [243683.539306] RBP: ffff88842ba49af8 R08: 0000000000000001 R09: ffff88840d17aaf8 [243683.539306] R10: 0000000000000001 R11: 00000000ffffffec R12: ffff88843c68c080 [243683.539306] R13: ffff88842ba49ae8 R14: 0000000000000001 R15: 0000000000000000 [243683.539307] FS: 0000000000000000(0000) GS:ffff88843ea80000(0000) knlGS:0000000000000000 [243683.539307] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [243683.539307] CR2: 00007f3234b31f90 CR3: 0000000002608001 CR4: 00000000003726e0 [243683.539307] Call Trace: [243683.539308] ? filp_close+0x2a/0x60 [243683.539308] ? put_files_struct.part.0+0x57/0xb0 [243683.539309] ? do_exit+0x321/0xa70 [243683.539309] ? do_group_exit+0x35/0x90 [243683.539309] ? __x64_sys_exit_group+0xf/0x10 [243683.539309] ? do_syscall_64+0x41/0x160 [243683.539309] ? entry_SYSCALL_64_after_hwframe+0x44/0xa9 [243684.753272] rcu: INFO: rcu_sched detected stalls on CPUs/tasks: [243684.753278] rcu: 1-...0: (1 GPs behind) idle=a5e/1/0x4000000000000000 softirq=7893711/7893712 fqs=2955 [243684.753280] (detected by 3, t=6002 jiffies, g=17109677, q=117817) [243684.753282] Sending NMI from CPU 3 to CPUs 1: [243684.754285] NMI backtrace for cpu 1 [243684.754285] CPU: 1 PID: 1527 Comm: qemu-system-x86 Tainted: P W O 5.4.63+ #1 [243684.754286] Hardware name: System manufacturer System Product Name/PRIME Z370-A, BIOS 2401 07/12/2019 [243684.754286] RIP: 0010:io_uring_flush+0x83/0x140 [243684.754287] Code: 89 ef e8 00 36 92 00 48 8b 83 e8 02 00 00 49 39 c5 74 52 4d 85 e4 74 70 48 8b 93 e8 02 00 00 48 8b 32 48 8b 4a 08 48 89 4e 08 <48> 89 31 48 89 12 48 89 52 08 48 8b 72 f8 81 4a a8 00 40 00 00 48 [243684.754287] RSP: 0018:ffff8881f20c3e28 EFLAGS: 00000002 [243684.754288] RAX: ffff888419cd94e0 RBX: ffff88842ba49800 RCX: ffff888419cd94e0 [243684.754288] RDX: ffff888419cd94e0 RSI: ffff888419cd94e0 RDI: ffff88842ba49af8 [243684.754289] RBP: ffff88842ba49af8 R08: 0000000000000001 R09: ffff88840d17aaf8 [243684.754289] R10: 0000000000000001 R11: 00000000ffffffec R12: ffff88843c68c080 [243684.754289] R13: ffff88842ba49ae8 R14: 0000000000000001 R15: 0000000000000000 [243684.754290] FS: 0000000000000000(0000) GS:ffff88843ea80000(0000) knlGS:0000000000000000 [243684.754290] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [243684.754291] CR2: 00007f3234b31f90 CR3: 0000000002608001 CR4: 00000000003726e0 [243684.754291] Call Trace: [243684.754291] ? filp_close+0x2a/0x60 [243684.754291] ? put_files_struct.part.0+0x57/0xb0 [243684.754292] ? do_exit+0x321/0xa70 [243684.754292] ? do_group_exit+0x35/0x90 [243684.754292] ? __x64_sys_exit_group+0xf/0x10 [243684.754293] ? do_syscall_64+0x41/0x160 [243684.754293] ? entry_SYSCALL_64_after_hwframe+0x44/0xa9
