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virtio-blk: restart s->rq reqs in vq AioContexts

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A virtio-blk device with the iothread-vq-mapping parameter has
per-virtqueue AioContexts. It is not thread-safe to process s->rq
requests in the BlockBackend AioContext since that may be different from
the virtqueue's AioContext to which this request belongs. The code
currently races and could crash.

Adapt virtio_blk_dma_restart_cb() to first split s->rq into per-vq lists
and then schedule a BH each vq's AioContext as necessary. This way
requests are safely processed in their vq's AioContext.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20240119135748.270944-5-stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2024-01-19 08:57:46 -05:00 • committed by Kevin Wolf
parent 3cdaf3dd4a
commit 71ee0cdd14
1 changed files with 33 additions and 11 deletions
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44
hw/block/virtio-blk.c
View file

@ -1156,16 +1156,11 @@ static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq)
static void virtio_blk_dma_restart_bh(void *opaque) static void virtio_blk_dma_restart_bh(void *opaque)
{ {
VirtIOBlock *s = opaque; VirtIOBlockReq *req = opaque;
VirtIOBlock *s = req->dev; /* we're called with at least one request */
VirtIOBlockReq *req;
MultiReqBuffer mrb = {}; MultiReqBuffer mrb = {};
WITH_QEMU_LOCK_GUARD(&s->rq_lock) {
req = s->rq;
s->rq = NULL;
}
while (req) { while (req) {
VirtIOBlockReq *next = req->next; VirtIOBlockReq *next = req->next;
if (virtio_blk_handle_request(req, &mrb)) { if (virtio_blk_handle_request(req, &mrb)) {
@ -1195,16 +1190,43 @@ static void virtio_blk_dma_restart_cb(void *opaque, bool running,
RunState state) RunState state)
{ {
VirtIOBlock *s = opaque; VirtIOBlock *s = opaque;
uint16_t num_queues = s->conf.num_queues;
if (!running) { if (!running) {
return; return;
} }
/* Paired with dec in virtio_blk_dma_restart_bh() */ /* Split the device-wide s->rq request list into per-vq request lists */
blk_inc_in_flight(s->conf.conf.blk); g_autofree VirtIOBlockReq **vq_rq = g_new0(VirtIOBlockReq *, num_queues);
VirtIOBlockReq *rq;
aio_bh_schedule_oneshot(blk_get_aio_context(s->conf.conf.blk), WITH_QEMU_LOCK_GUARD(&s->rq_lock) {
virtio_blk_dma_restart_bh, s); rq = s->rq;
s->rq = NULL;
}
while (rq) {
VirtIOBlockReq *next = rq->next;
uint16_t idx = virtio_get_queue_index(rq->vq);
rq->next = vq_rq[idx];
vq_rq[idx] = rq;
rq = next;
}
/* Schedule a BH to submit the requests in each vq's AioContext */
for (uint16_t i = 0; i < num_queues; i++) {
if (!vq_rq[i]) {
continue;
}
/* Paired with dec in virtio_blk_dma_restart_bh() */
blk_inc_in_flight(s->conf.conf.blk);
aio_bh_schedule_oneshot(s->vq_aio_context[i],
virtio_blk_dma_restart_bh,
vq_rq[i]);
}
} }
static void virtio_blk_reset(VirtIODevice *vdev) static void virtio_blk_reset(VirtIODevice *vdev)