NAS-134891 / 25.04.0 / linux: zvols: correctly detect flush requests (#17131) #281
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since 4.10, bio->bi_opf needs to be checked to determine all kinds of flush requests. this was the case prior to the commit referenced below, but the order of ifdefs was not the usual one (newest up top), which might have caused this to slip through. this fixes a regression when using zvols as Qemu block devices, but might have broken other use cases as well. the symptoms are that all sync writes from within a VM configured to use such a virtual block devices are ignored and treated as async writes by the host ZFS layer. this can be verified using fio in sync mode inside the VM, for example with fio \ --filename=/dev/sda --ioengine=libaio --loops=1 --size=10G \ --time_based --runtime=60 --group_reporting --stonewall --name=cc1 \ --description="CC1" --rw=write --bs=4k --direct=1 --iodepth=1 \ --numjobs=1 --sync=1 which shows an IOPS number way above what the physical device underneath supports, with "zpool iostat -r 1" on the hypervisor side showing no sync IO occuring during the benchmark. with the regression fixed, both fio inside the VM and the IO stats on the host show the expected numbers. Fixes: 846b598 "config: remove HAVE_REQ_OP_* and HAVE_REQ_*" Signed-off-by: Fabian-Gruenbichler <[email protected]> Co-authored-by: Alexander Motin <[email protected]> Reviewed-by: Alexander Motin <[email protected]> Reviewed-by: Tony Hutter <[email protected]>
bugclerk
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amotin
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Mar 19, 2025
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since 4.10, bio->bi_opf needs to be checked to determine all kinds of flush requests. this was the case prior to the commit referenced below, but the order of ifdefs was not the usual one (newest up top), which might have caused this to slip through.
this fixes a regression when using zvols as Qemu block devices, but might have broken other use cases as well. the symptoms are that all sync writes from within a VM configured to use such a virtual block devices are ignored and treated as async writes by the host ZFS layer.
this can be verified using fio in sync mode inside the VM, for example with
fio
--filename=/dev/sda --ioengine=libaio --loops=1 --size=10G
--time_based --runtime=60 --group_reporting --stonewall --name=cc1
--description="CC1" --rw=write --bs=4k --direct=1 --iodepth=1
--numjobs=1 --sync=1
which shows an IOPS number way above what the physical device underneath supports, with "zpool iostat -r 1" on the hypervisor side showing no sync IO occuring during the benchmark.
with the regression fixed, both fio inside the VM and the IO stats on the host show the expected numbers.
Fixes: 846b598
"config: remove HAVE_REQ_OP_* and HAVE_REQ_*"
Reviewed-by: Alexander Motin [email protected]
Reviewed-by: Tony Hutter [email protected]
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Signed-off-by.