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For reference, here is the stack of systemd-udevd seen in the hang:
[ 1558.214013] INFO: task systemd-udevd:1778 blocked for more than 120 seconds.
[ 1558.214318] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this
message.
[ 1558.214556] systemd-udevd D 00003fff8dbdf7a0 0 1778 1 0x00040000
[ 1558.214637] Call Trace:
[ 1558.214673] [c000000004ad3790] [c0000000007aac20]
schedule_timeout+0x180/0x2f0 (unreliable)
[ 1558.214779] [c000000004ad3960] [c0000000000158d0] __switch_to+0x200/0x350
[ 1558.214870] [c000000004ad39c0] [c0000000007adbb4] __schedule+0x414/0x9e0
[ 1558.214961] [c000000004ad3a90] [c0000000003b4e54]
blk_mq_freeze_queue_wait+0x64/0xd0
[ 1558.215107] [c000000004ad3af0] [d000000034011964]
nvme_revalidate_disk+0xd4/0x3a0 [nvme]
[ 1558.215386] [c000000004ad3b90] [c0000000003c2398]
rescan_partitions+0x98/0x390
[ 1558.215508] [c000000004ad3c60] [c0000000003bb7ac]
__blkdev_reread_part+0x9c/0xd0
[ 1558.215599] [c000000004ad3c90] [c0000000003bb818]
blkdev_reread_part+0x38/0x70
[ 1558.215935] [c000000004ad3cc0] [c0000000003bc334] blkdev_ioctl+0x3b4/0xb80
[ 1558.216016] [c000000004ad3d20] [c0000000002cbcd0] block_ioctl+0x70/0x90
[ 1558.216114] [c000000004ad3d40] [c000000000296b38] do_vfs_ioctl+0x458/0x740
[ 1558.216192] [c000000004ad3dd0] [c000000000296ee4] SyS_ioctl+0xc4/0xe0
[ 1558.216275] [c000000004ad3e30] [c00000000000a17c] system_call+0x38/0xb4
It appears that systemd-udevd is triggering every time HTX writes to the
boot sector (partition table) of the raw drive, and this is causing the
revalidate calls which expose the issue with the block driver mq freeze.
With a partition table on each drive, HTX will no longer be writing the
partition table and no longer triggering systemd to re-read the
partition table and try to freeze I/O.
The fix for this is provided by the following upstream commit:
966d2b0 percpu-refcount: fix reference leak during percpu-atomic
transition
which needs to be pulled into 16.04 (as well as newer releases).
** Affects: linux (Ubuntu)
Importance: Undecided
Assignee: Taco Screen team (taco-screen-team)
Status: New
** Tags: architecture-ppc64le bugnameltc-148242 severity-critical
targetmilestone-inin16042
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systemd-udevd hung in blk_mq_freeze_queue_wait testing unpartitioned NVMe drive
https://bugs.launchpad.net/bugs/1662673
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