Re: [PATCH] block: cleanup and fix batch completion adding conditions

Shinichiro Kawasaki
2025-02-19T07:26:29Z

CC+: Alan,

On Feb 13, 2025 / 08:18, Jens Axboe wrote:
> The conditions for whether or not a request is allowed adding to a
> completion batch are a bit hard to read, and they also have a few
> issues. One is that ioerror may indeed be a random value on passthrough,
> and it's being checked unconditionally of whether or not the given
> request is a passthrough request or not.
>
> Rewrite the conditions to be separate for easier reading, and only check
> ioerror for non-passthrough requests. This fixes an issue with bio
> unmapping on passthrough, where it fails getting added to a batch. This
> both leads to suboptimal performance, and may trigger a potential
> schedule-under-atomic condition for polled passthrough IO.
>
> Fixes: f794f3351f26 ("block: add support for blk_mq_end_request_batch()")
> Signed-off-by: Jens Axboe <axboe@kernel.dk>

I observed the blktests test case nvme/039 failure with v6.14-rc3 kernel. I
bisected and found that this patch in the v6.14-rc3 is the trigger.

The test run output is as follows:

nvme/039 => nvme0n1 (test error logging) [failed]
runtime 5.378s ... 5.354s
--- tests/nvme/039.out 2024-09-20 11:20:26.405380875 +0900
+++ /home/shin/Blktests/blktests/results/nvme0n1/nvme/039.out.bad 2025-02-19 16:13:05.061387179 +0900
@@ -1,7 +1,3 @@
Running nvme/039
- Read(0x2) @ LBA 0, 1 blocks, Unrecovered Read Error (sct 0x2 / sc 0x81) DNR
- Read(0x2) @ LBA 0, 1 blocks, Unknown (sct 0x3 / sc 0x75) DNR
- Write(0x1) @ LBA 0, 1 blocks, Write Fault (sct 0x2 / sc 0x80) DNR
Identify(0x6), Access Denied (sct 0x2 / sc 0x86) DNR cdw10=0x1 cdw11=0x0 cdw12=0x0 cdw13=0x0 cdw14=0x0 cdw15=0x0
- Read(0x2), Invalid Command Opcode (sct 0x0 / sc 0x1) DNR cdw10=0x0 cdw11=0x0 cdw12=0x1 cdw13=0x0 cdw14=0x0 cdw15=0x0
Test complete

The test case does error injection. Test method requires reconsideration to
adjust to this kernel change, probably. Help for fix will be appreciated.