Rob Norris a49c957299 linux/zvol_os: fix crash with blk-mq on Linux 4.19
03987f71e3 (#16069) added a workaround to get the blk-mq hardware
context for older kernels that don't cache it in the struct request.
However, this workaround appears to be incomplete.

In 4.19, the rq data context is optional. If its not initialised, then
the cached rq->cpu will be -1, and so using it to index into mq_map
causes a crash.

Given that the upstream 4.19 is now in extended LTS and rarely seen,
RHEL8 4.18+ has long carried "modern" blk-mq support, and the cached
hardware context has been available since 5.1, I'm not going to huge
lengths to get queue selection correct for the very few people that are
likely to feel it. To that end, we simply call raw_smp_processor_id() to
get a valid CPU id and use that instead.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com>
Reviewed-by: Paul Dagnelie <paul.dagnelie@klarasystems.com>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Closes #17597
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OpenZFS is an advanced file system and volume manager which was originally developed for Solaris and is now maintained by the OpenZFS community. This repository contains the code for running OpenZFS on Linux and FreeBSD.

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Official Resources

Installation

Full documentation for installing OpenZFS on your favorite operating system can be found at the Getting Started Page.

Contribute & Develop

We have a separate document with contribution guidelines.

We have a Code of Conduct.

Release

OpenZFS is released under a CDDL license. For more details see the NOTICE, LICENSE and COPYRIGHT files; UCRL-CODE-235197

Supported Kernels

  • The META file contains the officially recognized supported Linux kernel versions.
  • Supported FreeBSD versions are any supported branches and releases starting from 13.0-RELEASE.
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