Hi, I've been experiencing this problem intermittently since December of last year after upgrading some existing servers to Debian stable (buster). I can't reproduce it at will and it can sometimes take several months to happen again, although it has just happened twice in 3 days on one host. What happens is that all IO to particular MD devices seems to freeze. At this point I generally have no option but to power cycle the server as an orderly shutdown can't be completed. These servers are Xen hypervisors, and very occasionally I or a guest administrator has been able to shut down a guest and then things seem to become unblocked. I am aware that this could mean it could be a Xen issue and I'm pursuing that angle as well. The version of the Xen hypervisor in use did change as well as the OS upgrade. In terms of logging, this is the sort of thing I get: Jun 12 12:04:40 clockwork kernel: [216427.246183] INFO: task md5_raid1:205 blocked for more than 120 seconds. Jun 12 12:04:40 clockwork kernel: [216427.246995] Not tainted 4.19.0-16-amd64 #1 Debian 4.19.181-1 Jun 12 12:04:40 clockwork kernel: [216427.247852] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. Jun 12 12:04:40 clockwork kernel: [216427.248674] md5_raid1 D 0 205 2 0x80000000 Jun 12 12:04:40 clockwork kernel: [216427.249534] Call Trace: Jun 12 12:04:40 clockwork kernel: [216427.250368] __schedule+0x29f/0x840 Jun 12 12:04:40 clockwork kernel: [216427.251788] ? _raw_spin_unlock_irqrestore+0x14/0x20 Jun 12 12:04:40 clockwork kernel: [216427.253078] schedule+0x28/0x80 Jun 12 12:04:40 clockwork kernel: [216427.253945] md_super_wait+0x6e/0xa0 [md_mod] Jun 12 12:04:40 clockwork kernel: [216427.254812] ? finish_wait+0x80/0x80 Jun 12 12:04:40 clockwork kernel: [216427.256139] md_bitmap_wait_writes+0x93/0xa0 [md_mod] Jun 12 12:04:40 clockwork kernel: [216427.256994] ? md_bitmap_get_counter+0x42/0xd0 [md_mod] Jun 12 12:04:40 clockwork kernel: [216427.257787] md_bitmap_daemon_work+0x1f7/0x370 [md_mod] Jun 12 12:04:40 clockwork kernel: [216427.258608] ? md_rdev_init+0xb0/0xb0 [md_mod] Jun 12 12:04:40 clockwork kernel: [216427.259553] md_check_recovery+0x41/0x530 [md_mod] Jun 12 12:04:40 clockwork kernel: [216427.260304] raid1d+0x5c/0xf10 [raid1] Jun 12 12:04:40 clockwork kernel: [216427.261096] ? lock_timer_base+0x67/0x80 Jun 12 12:04:40 clockwork kernel: [216427.261863] ? _raw_spin_unlock_irqrestore+0x14/0x20 Jun 12 12:04:40 clockwork kernel: [216427.262659] ? try_to_del_timer_sync+0x4d/0x80 Jun 12 12:04:40 clockwork kernel: [216427.263436] ? del_timer_sync+0x37/0x40 Jun 12 12:04:40 clockwork kernel: [216427.264189] ? schedule_timeout+0x173/0x3b0 Jun 12 12:04:40 clockwork kernel: [216427.264911] ? md_rdev_init+0xb0/0xb0 [md_mod] Jun 12 12:04:40 clockwork kernel: [216427.265664] ? md_thread+0x94/0x150 [md_mod] Jun 12 12:04:40 clockwork kernel: [216427.266412] ? process_checks+0x4a0/0x4a0 [raid1] Jun 12 12:04:40 clockwork kernel: [216427.267124] md_thread+0x94/0x150 [md_mod] Jun 12 12:04:40 clockwork kernel: [216427.267842] ? finish_wait+0x80/0x80 Jun 12 12:04:40 clockwork kernel: [216427.268539] kthread+0x112/0x130 Jun 12 12:04:40 clockwork kernel: [216427.269231] ? kthread_bind+0x30/0x30 Jun 12 12:04:40 clockwork kernel: [216427.269903] ret_from_fork+0x35/0x40 Jun 12 12:04:40 clockwork kernel: [216427.270590] INFO: task md2_raid1:207 blocked for more than 120 seconds. Jun 12 12:04:40 clockwork kernel: [216427.271260] Not tainted 4.19.0-16-amd64 #1 Debian 4.19.181-1 Jun 12 12:04:40 clockwork kernel: [216427.271942] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. Jun 12 12:04:40 clockwork kernel: [216427.272721] md2_raid1 D 0 207 2 0x80000000 Jun 12 12:04:40 clockwork kernel: [216427.273432] Call Trace: Jun 12 12:04:40 clockwork kernel: [216427.274172] __schedule+0x29f/0x840 Jun 12 12:04:40 clockwork kernel: [216427.274869] schedule+0x28/0x80 Jun 12 12:04:40 clockwork kernel: [216427.275543] io_schedule+0x12/0x40 Jun 12 12:04:40 clockwork kernel: [216427.276208] wbt_wait+0x205/0x300 Jun 12 12:04:40 clockwork kernel: [216427.276861] ? wbt_wait+0x300/0x300 Jun 12 12:04:40 clockwork kernel: [216427.277503] rq_qos_throttle+0x31/0x40 Jun 12 12:04:40 clockwork kernel: [216427.278193] blk_mq_make_request+0x111/0x530 Jun 12 12:04:40 clockwork kernel: [216427.278876] generic_make_request+0x1a4/0x400 Jun 12 12:04:40 clockwork kernel: [216427.279657] ? try_to_wake_up+0x54/0x470 Jun 12 12:04:40 clockwork kernel: [216427.280400] submit_bio+0x45/0x130 Jun 12 12:04:40 clockwork kernel: [216427.281136] ? md_super_write.part.63+0x90/0x120 [md_mod] Jun 12 12:04:40 clockwork kernel: [216427.281788] md_update_sb.part.65+0x3a8/0x8e0 [md_mod] Jun 12 12:04:40 clockwork kernel: [216427.282480] ? md_rdev_init+0xb0/0xb0 [md_mod] Jun 12 12:04:40 clockwork kernel: [216427.283106] md_check_recovery+0x272/0x530 [md_mod] Jun 12 12:04:40 clockwork kernel: [216427.283738] raid1d+0x5c/0xf10 [raid1] Jun 12 12:04:40 clockwork kernel: [216427.284345] ? __schedule+0x2a7/0x840 Jun 12 12:04:40 clockwork kernel: [216427.284939] ? md_rdev_init+0xb0/0xb0 [md_mod] Jun 12 12:04:40 clockwork kernel: [216427.285522] ? schedule+0x28/0x80 Jun 12 12:04:40 clockwork kernel: [216427.286121] ? schedule_timeout+0x26d/0x3b0 Jun 12 12:04:40 clockwork kernel: [216427.286702] ? __schedule+0x2a7/0x840 Jun 12 12:04:40 clockwork kernel: [216427.287279] ? md_rdev_init+0xb0/0xb0 [md_mod] Jun 12 12:04:40 clockwork kernel: [216427.287871] ? md_thread+0x94/0x150 [md_mod] Jun 12 12:04:40 clockwork kernel: [216427.288458] ? process_checks+0x4a0/0x4a0 [raid1] Jun 12 12:04:40 clockwork kernel: [216427.289062] md_thread+0x94/0x150 [md_mod] Jun 12 12:04:40 clockwork kernel: [216427.289663] ? finish_wait+0x80/0x80 Jun 12 12:04:40 clockwork kernel: [216427.290288] kthread+0x112/0x130 Jun 12 12:04:40 clockwork kernel: [216427.290858] ? kthread_bind+0x30/0x30 Jun 12 12:04:40 clockwork kernel: [216427.291433] ret_from_fork+0x35/0x40 Anyone seen anything like this before or have any suggestions for what to try next? It's not really feasible for me to try to see if it happens without running as a Xen dom0 because even if it doesn't happen for 2 months I won't have confidence… Thanks, Andy
