Re: [PATCH v9 00/13] blk: honor isolcpus configuration

Aaron Tomlin
2026-03-31T13:38:34Z

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On Tue, Mar 31, 2026 at 09:01:48AM +0800, Ming Lei wrote:
> Can you share the bug report link?
>
> IMO, it should be solved as a backportable patch first if possible.

Hi Ming,

Thanks for taking a look at the series.

Here is the link to the kernel test robot's bug report:
https://lore.kernel.org/oe-lkp/202509101342.a803ecaa-lkp@intel.com

Regarding a backportable patch, the NULL pointer dereference is actually
not an existing mainline bug. It was a regression introduced specifically
by the previous iteration of this series, specifically by Patch 10:
"blk-mq: use hk cpus only when isolcpus=io_queue is enabled".

The previously implementation introduced the global static
blk_hk_online_mask variable, which caused the race condition during the
robot's cpuhotplug stress tests. Because that flawed logic was confined to
the unmerged v8 patches and never made it into a mainline release, there is
nothing to backport to stable trees.

Version 9 simply drops that global mask approach entirely in favour of
local data_race(cpu_online_mask) snapshots, fixing the architectural flaw
within the series itself.

Kind regards,
--
Aaron Tomlin

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