Searched hist:c8bf923d5eeed0b2bbe26feb37bb399ec1a894f5 (Results 1 – 1 of 1) sorted by relevance
| /qemu/tests/unit/ |
| H A D | test-bdrv-drain.c | c8bf923d5eeed0b2bbe26feb37bb399ec1a894f5 Tue Sep 12 23:10:34 UTC 2023 Stefan Hajnoczi <stefanha@redhat.com> test-bdrv-drain: avoid race with BH in IOThread drain test
This patch fixes a race condition in test-bdrv-drain that is difficult
to reproduce. test-bdrv-drain sometimes fails without an error message
on the block pull request sent by Kevin Wolf on Sep 4, 2023. I was able
to reproduce it locally and found that "block-backend: process I/O in
the current AioContext" (in this patch series) is the first commit where
it reproduces.
I do not know why "block-backend: process I/O in the current AioContext"
exposes this bug. It might be related to the fact that the test's preadv
request runs in the main thread instead of IOThread a after my commit.
That might simply change the timing of the test.
Now on to the race condition in test-bdrv-drain. The main thread
schedules a BH in IOThread a and then drains the BDS:
aio_bh_schedule_oneshot(ctx_a, test_iothread_main_thread_bh, &data);
/* The request is running on the IOThread a. Draining its block device
* will make sure that it has completed as far as the BDS is concerned,
* but the drain in this thread can continue immediately after
* bdrv_dec_in_flight() and aio_ret might be assigned only slightly
* later. */
do_drain_begin(drain_type, bs);
If the BH completes before do_drain_begin() then there is nothing to
worry about.
If the BH invokes bdrv_flush() before do_drain_begin(), then
do_drain_begin() waits for it to complete.
The problematic case is when do_drain_begin() runs before the BH enters
bdrv_flush(). Then do_drain_begin() misses the BH and the drain
mechanism has failed in quiescing I/O.
Fix this by incrementing the in_flight counter so that do_drain_begin()
waits for test_iothread_main_thread_bh().
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20230912231037.826804-3-stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
|