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Avoid vq_lock drop in vdev_queue_aggregate(). #12297

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Aug 17, 2021
Merged

Avoid vq_lock drop in vdev_queue_aggregate(). #12297

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63 changes: 34 additions & 29 deletions module/zfs/vdev_queue.c
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Original file line number Diff line number Diff line change
Expand Up @@ -599,7 +599,6 @@ static zio_t *
vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
{
zio_t *first, *last, *aio, *dio, *mandatory, *nio;
zio_link_t *zl = NULL;
uint64_t maxgap = 0;
uint64_t size;
uint64_t limit;
Expand Down Expand Up @@ -797,19 +796,12 @@ vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
ASSERT3U(abd_get_size(aio->io_abd), ==, aio->io_size);

/*
* We need to drop the vdev queue's lock during zio_execute() to
* avoid a deadlock that we could encounter due to lock order
* reversal between vq_lock and io_lock in zio_change_priority().
* Callers must call zio_vdev_io_bypass() and zio_execute() for
* aggregated (parent) I/Os so that we could avoid dropping the
* queue's lock here to avoid a deadlock that we could encounter
* due to lock order reversal between vq_lock and io_lock in
* zio_change_priority().
*/
mutex_exit(&vq->vq_lock);
while ((dio = zio_walk_parents(aio, &zl)) != NULL) {
ASSERT3U(dio->io_type, ==, aio->io_type);

zio_vdev_io_bypass(dio);
zio_execute(dio);
}
mutex_enter(&vq->vq_lock);

return (aio);
}

Expand Down Expand Up @@ -847,23 +839,24 @@ vdev_queue_io_to_issue(vdev_queue_t *vq)
ASSERT3U(zio->io_priority, ==, p);

aio = vdev_queue_aggregate(vq, zio);
if (aio != NULL)
if (aio != NULL) {
zio = aio;
else
} else {
vdev_queue_io_remove(vq, zio);

/*
* If the I/O is or was optional and therefore has no data, we need to
* simply discard it. We need to drop the vdev queue's lock to avoid a
* deadlock that we could encounter since this I/O will complete
* immediately.
*/
if (zio->io_flags & ZIO_FLAG_NODATA) {
mutex_exit(&vq->vq_lock);
zio_vdev_io_bypass(zio);
zio_execute(zio);
mutex_enter(&vq->vq_lock);
goto again;
/*
* If the I/O is or was optional and therefore has no data, we
* need to simply discard it. We need to drop the vdev queue's
* lock to avoid a deadlock that we could encounter since this
* I/O will complete immediately.
*/
if (zio->io_flags & ZIO_FLAG_NODATA) {
mutex_exit(&vq->vq_lock);
zio_vdev_io_bypass(zio);
zio_execute(zio);
mutex_enter(&vq->vq_lock);
goto again;
}
}

vdev_queue_pending_add(vq, zio);
Expand All @@ -876,7 +869,8 @@ zio_t *
vdev_queue_io(zio_t *zio)
{
vdev_queue_t *vq = &zio->io_vd->vdev_queue;
zio_t *nio;
zio_t *dio, *nio;
zio_link_t *zl = NULL;

if (zio->io_flags & ZIO_FLAG_DONT_QUEUE)
return (zio);
Expand Down Expand Up @@ -923,6 +917,11 @@ vdev_queue_io(zio_t *zio)
return (NULL);

if (nio->io_done == vdev_queue_agg_io_done) {
while ((dio = zio_walk_parents(nio, &zl)) != NULL) {
ASSERT3U(dio->io_type, ==, nio->io_type);
zio_vdev_io_bypass(dio);
zio_execute(dio);
}
zio_nowait(nio);
return (NULL);
}
Expand All @@ -934,7 +933,8 @@ void
vdev_queue_io_done(zio_t *zio)
{
vdev_queue_t *vq = &zio->io_vd->vdev_queue;
zio_t *nio;
zio_t *dio, *nio;
zio_link_t *zl = NULL;

mutex_enter(&vq->vq_lock);

Expand All @@ -947,6 +947,11 @@ vdev_queue_io_done(zio_t *zio)
while ((nio = vdev_queue_io_to_issue(vq)) != NULL) {
mutex_exit(&vq->vq_lock);
if (nio->io_done == vdev_queue_agg_io_done) {
while ((dio = zio_walk_parents(nio, &zl)) != NULL) {
ASSERT3U(dio->io_type, ==, nio->io_type);
zio_vdev_io_bypass(dio);
zio_execute(dio);
}
zio_nowait(nio);
} else {
zio_vdev_io_reissue(nio);
Expand Down