Am 12.02.2025 um 10:32 hat Hanna Czenczek geschrieben: > RBD schedules the request completion code (qemu_rbd_finish_bh()) to run > in the BDS's AioContext. The intent seems to be to run it in the same > context that the original request coroutine ran in, i.e. the thread on > whose stack the RBDTask object exists (see qemu_rbd_start_co()). > > However, with multiqueue, that thread is not necessarily the same as the > BDS's AioContext. Instead, we need to remember the actual AioContext > and schedule the completion BH there. > > Buglink: https://issues.redhat.com/browse/RHEL-67115
Please add a short summary of what actually happens to the commit message. I had to check the link to remember what the symptoms are. > Reported-by: Junyao Zhao <junz...@redhat.com> > Signed-off-by: Hanna Czenczek <hre...@redhat.com> > --- > I think I could also drop RBDTask.ctx and just use > `qemu_coroutine_get_aio_context(RBDTask.co)` instead, but this is the > version of the patch that was tested and confirmed to fix the issue (I > don't have a local reproducer), so I thought I'll post this first. Did you figure out why it even makes a difference in which thread qemu_rbd_finish_bh() runs? For context: static void qemu_rbd_finish_bh(void *opaque) { RBDTask *task = opaque; task->complete = true; aio_co_wake(task->co); } This looks as if it should be working in any thread, except maybe for a missing barrier after updating task->complete - but I think the failure mode for that would be a hang in qemu_rbd_start_co(). > block/rbd.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/block/rbd.c b/block/rbd.c > index af984fb7db..9d4e0817e0 100644 > --- a/block/rbd.c > +++ b/block/rbd.c > @@ -102,7 +102,7 @@ typedef struct BDRVRBDState { > } BDRVRBDState; > > typedef struct RBDTask { > - BlockDriverState *bs; > + AioContext *ctx; > Coroutine *co; > bool complete; > int64_t ret; > @@ -1269,8 +1269,7 @@ static void qemu_rbd_completion_cb(rbd_completion_t c, > RBDTask *task) > { > task->ret = rbd_aio_get_return_value(c); > rbd_aio_release(c); > - aio_bh_schedule_oneshot(bdrv_get_aio_context(task->bs), > - qemu_rbd_finish_bh, task); > + aio_bh_schedule_oneshot(task->ctx, qemu_rbd_finish_bh, task); > } > > static int coroutine_fn qemu_rbd_start_co(BlockDriverState *bs, > @@ -1281,7 +1280,10 @@ static int coroutine_fn > qemu_rbd_start_co(BlockDriverState *bs, > RBDAIOCmd cmd) > { > BDRVRBDState *s = bs->opaque; > - RBDTask task = { .bs = bs, .co = qemu_coroutine_self() }; > + RBDTask task = { > + .ctx = qemu_get_current_aio_context(), > + .co = qemu_coroutine_self(), > + }; > rbd_completion_t c; > int r; Nothing wrong I can see about the change, but I don't understand why it fixes the problem. Kevin