zvol: Remove broken blk-mq optimization #15439
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This reverts commit aefb6a2. aefb6a2 temporally disabled blk-mq until we could fix a fix for openzfs#15351. We now have that fix (see next commit) fix so revert aefb6a2. Signed-off-by: Tony Hutter <hutter2@llnl.gov>
This fix removes a dubious optimization in zfs_uiomove_bvec_rq() that saved the iterator contents of a rq_for_each_segment(). This optimization allowed restoring the "saved state" from a previous rq_for_each_segment() call on the same uio so that you wouldn't need to iterate though each bvec on every zfs_uiomove_bvec_rq() call. However, if the kernel is manipulating the requests/bios/bvecs under the covers between zfs_uiomove_bvec_rq() calls, then it could result in corruption from using the "saved state". This optimization results in an unbootable system after installing an OS on a zvol with blk-mq enabled. Fixes: openzfs#15351 Signed-off-by: Tony Hutter <hutter2@llnl.gov>
behlendorf
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Oct 24, 2023
ixhamza
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Nov 20, 2023
This reverts commit aefb6a2. aefb6a2 temporally disabled blk-mq until we could fix a fix for Signed-off-by: Tony Hutter <hutter2@llnl.gov> Closes openzfs#15439
lundman
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Dec 12, 2023
This reverts commit aefb6a2. aefb6a2 temporally disabled blk-mq until we could fix a fix for Signed-off-by: Tony Hutter <hutter2@llnl.gov> Closes openzfs#15439
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Motivation and Context
Fixes: #15351
Description
This fix removes a dubious optimization in zfs_uiomove_bvec_rq() that saved the iterator contents of a rq_for_each_segment(). This optimization allowed restoring the "saved state" from a previous rq_for_each_segment() call on the same uio so that you wouldn't need to iterate though each bvec on every zfs_uiomove_bvec_rq() call. However, if the kernel is manipulating the requests/bios/bvecs under the covers between zfs_uiomove_bvec_rq() calls, then it could result in corruption from using the "saved state". This optimization results in an unbootable system after installing an OS on a zvol with blk-mq enabled.
With this PR applied the problem goes away.
How Has This Been Tested?
Tried to install both Ubuntu and Fedora from a blk-mq enabled zvol and verified both failed to boot after the install. Re-ran the same test with this patch applied and saw them both correctly boot.
Types of changes
Checklist:
Signed-off-by.