Kernel soft lockup with blk_mq_update in traces
This document (000020248) is provided subject to the disclaimer at the end of this document.
SUSE Linux Enterprise Server 15
kernel: [1726320.308008] NMI watchdog: BUG: soft lockup - CPU#104 stuck for 23s!
and followed by
kernel: [1726320.336383] ? blk_mq_update_queue_map+0x20/0x20
in the logs.
These stats are the ones shown in
In the Azure Enviroment the Hyper-V storvsc driver in Linux can set the
parameter value too high, which can result in allocating too many "tags" when operating with blk-mq enabled.
There are several workarounds possible:
1. The most obvious would be to move to a Linux kernel version 5.0 or later. But this is the most problematic in a Production Enviroment as it depends on whether a Kernel 5.0 or later is available.
2. Disable blk-mq and use the older block subsystem in the Linux kernel.
This workaround could negate some I/O performance gains of the parallelism that the blk-mq subsystem provides.
To apply this workaround the
is removed from the kernel boot line, and a reboot is required.
3. Disable disk I/O stats.
This can be done on-the-fly on a per-disk basis on a running system by
echo "0" /sys/block/<device>/queue/iostats
This has to be done for each disk device in the System and is not persistent over a reboot.
4. Reduce the "can_queue" value.
This value cannot be set directly. The desired effect can be achieved by adding the kernel boot line options
a reboot is required during which these values will then be passed to the hv_storvsc.
Option 4 only works on Azure. Option 3 is not persistent. Option 1 might not be possible.
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- Document ID:000020248
- Creation Date: 09-Jun-2021
- Modified Date:09-Jun-2021
- SUSE Linux Enterprise Server
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