Message-ID: <aXOGrXo3AbXPHA-K@fedora>
Date: Fri, 23 Jan 2026 22:33:17 +0800
From: Ming Lei <ming.lei@...hat.com>
To: Alexander Atanasov <alex@...olabs.com>
Cc: Shuah Khan <shuah@...nel.org>, linux-block@...r.kernel.org,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests: ublk: use tmpdir for scratch files and
 improve relative paths use

On Fri, Jan 23, 2026 at 03:59:31PM +0200, Alexander Atanasov wrote:
> On 23 Jan 2026, at 15:33, Ming Lei <ming.lei@...hat.com> wrote:
> > 
> > On Fri, Jan 23, 2026 at 11:20:36AM +0000, Alexander Atanasov wrote:
> >> Create a temp dir for temporary files and use it instead of
> >> placing them inside source tree.
> > 
> > Many temporary files are backing files of file storage target, so far
> > the code requires O_DIRECT, or the size could be a bit big.
> > 
> > In case of ramfs/tmpfs of temp dir, it may cause problem for tests.
> > 
> 
> I am aware of O_DIRECT problem but you can export different TMPDIR that has working O_DIRECT.

Can you share how to export TMPDIR capable of O_DIRECT?

> 
> I use sshfs mount of the build to run the tests and that is a problem sshfs/fuse does not
> do O_DIRECT too.
> 
> I think test_generic_06.sh is the only one that fails due to this(thou I still have to investigate).
> 
> If O_DIRECT is required by the tests it may be possible to go thru a RAM disk which does support it,
> so it works eveerywhere
> 
> Other option is to preserve working in source tree as it is now, and just add a variable to specify working directory -
> UBLK_TMPDIR or something.
> 
> 
> I get a lot of out of order io - between 0 and 10 on average on my test setup:
> tools/testing/selftests/ublk/test_generic_01.sh 
> Attached 3 probes
> io_out_of_order: exp 564688 actual 564648
> io_out_of_order: exp 564648 actual 565584
> io_out_of_order: exp 565584 actual 564688
> io_out_of_order: exp 565592 actual 564688
> io_out_of_order: exp 566328 actual 565592
> io_out_of_order: exp 882256 actual 882248
> io_out_of_order: exp 883032 actual 882912
> io_out_of_order: exp 882912 actual 883040
> io_out_of_order: exp 883040 actual 883032
> 
> 
> generic_01 : [FAIL]
> 
> All rq-s are there just reordered , AFAIK blk-mq does not guarantee that requests will be completed in order, what’s the idea to catch this and

If there is just 0 ~ 10, it could be fine. But if all are reorderd,
something must be wrong. One improvement could be check if there is too
many reorder...

Actually what I am trying to test is to make sure same order is observed
from both ublk driver dispatch code path and ublk target io handling code
path, because io_uring task work schedule uses llist, which may introduce io
reorder.

However, that involves ublk kprobe/kfunc trace, which may not be stable,
so I simply check the end-to-end IO order. Sometimes blk-mq IO queue/dispatch
may re-order IO.

I guess the following change may avoid the re-order, but batch IO case may
not be covered:

diff --git a/tools/testing/selftests/ublk/test_generic_01.sh b/tools/testing/selftests/ublk/test_generic_01.sh
index 21a31cd5491a..5805da4c84c5 100755
--- a/tools/testing/selftests/ublk/test_generic_01.sh
+++ b/tools/testing/selftests/ublk/test_generic_01.sh
@@ -29,14 +29,8 @@ if ! kill -0 "$btrace_pid" > /dev/null 2>&1; then
        exit "$UBLK_SKIP_CODE"
 fi

-# run fio over this ublk disk
-fio --name=write_seq \
-    --filename=/dev/ublkb"${dev_id}" \
-    --ioengine=libaio --iodepth=16 \
-    --rw=write \
-    --size=512M \
-    --direct=1 \
-    --bs=4k > /dev/null 2>&1
+taskset -c 0 dd if=/dev/zero of=/dev/ublkb"${dev_id}" bs=1M count=256 oflag=direct > /dev/null 2>&1
+


> consider it an error? (Latest tree with batch io and batch io fixes on top of if that matters)

Never observe generic_01 failure in my test VM and hardware.

My kernel config is based on Fedora, maybe scheduler config option makes the difference.



Thanks,
Ming

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