vduse_blk_detach_ctx() waits for in-flight requests using
AIO_WAIT_WHILE(). This is not allowed according to a comment in
bdrv_set_aio_context_commit():
/*
* Take the old AioContex when detaching it from bs.
* At this point, new_context lock is already acquired, and we are now
* also taking old_context. This is safe as long as bdrv_detach_aio_context
* does not call AIO_POLL_WHILE().
*/
Use this opportunity to rewrite the drain code in vduse-blk:
- Use the BlockExport refcount so that vduse_blk_exp_delete() is only
called when there are no more requests in flight.
- Implement .drained_poll() so in-flight request coroutines are stopped
by the time .bdrv_detach_aio_context() is called.
- Remove AIO_WAIT_WHILE() from vduse_blk_detach_ctx() to solve the
.bdrv_detach_aio_context() constraint violation. It's no longer
needed due to the previous changes.
- Always handle the VDUSE file descriptor, even in drained sections. The
VDUSE file descriptor doesn't submit I/O, so it's safe to handle it in
drained sections. This ensures that the VDUSE kernel code gets a fast
response.
- Suspend virtqueue fd handlers in .drained_begin() and resume them in
.drained_end(). This eliminates the need for the
aio_set_fd_handler(is_external=true) flag, which is being removed from
QEMU.
This is a long list but splitting it into individual commits would
probably lead to git bisect failures - the changes are all related.
Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
---
block/export/vduse-blk.c | 132 +++++++++++++++++++++++++++------------
1 file changed, 93 insertions(+), 39 deletions(-)
diff --git a/block/export/vduse-blk.c b/block/export/vduse-blk.c
index f7ae44e3ce..35dc8fcf45 100644
--- a/block/export/vduse-blk.c
+++ b/block/export/vduse-blk.c
@@ -31,7 +31,8 @@ typedef struct VduseBlkExport {
VduseDev *dev;
uint16_t num_queues;
char *recon_file;
- unsigned int inflight;
+ unsigned int inflight; /* atomic */
+ bool vqs_started;
} VduseBlkExport;
typedef struct VduseBlkReq {
@@ -41,13 +42,24 @@ typedef struct VduseBlkReq {
static void vduse_blk_inflight_inc(VduseBlkExport *vblk_exp)
{
- vblk_exp->inflight++;
+ if (qatomic_fetch_inc(&vblk_exp->inflight) == 0) {
+ /* Prevent export from being deleted */
+ aio_context_acquire(vblk_exp->export.ctx);
+ blk_exp_ref(&vblk_exp->export);
+ aio_context_release(vblk_exp->export.ctx);
+ }
}
static void vduse_blk_inflight_dec(VduseBlkExport *vblk_exp)
{
- if (--vblk_exp->inflight == 0) {
+ if (qatomic_fetch_dec(&vblk_exp->inflight) == 1) {
+ /* Wake AIO_WAIT_WHILE() */
aio_wait_kick();
+
+ /* Now the export can be deleted */
+ aio_context_acquire(vblk_exp->export.ctx);
+ blk_exp_unref(&vblk_exp->export);
+ aio_context_release(vblk_exp->export.ctx);
}
}
@@ -124,8 +136,12 @@ static void vduse_blk_enable_queue(VduseDev *dev,
VduseVirtq *vq)
{
VduseBlkExport *vblk_exp = vduse_dev_get_priv(dev);
+ if (!vblk_exp->vqs_started) {
+ return; /* vduse_blk_drained_end() will start vqs later */
+ }
+
aio_set_fd_handler(vblk_exp->export.ctx, vduse_queue_get_fd(vq),
- true, on_vduse_vq_kick, NULL, NULL, NULL, vq);
+ false, on_vduse_vq_kick, NULL, NULL, NULL, vq);
/* Make sure we don't miss any kick afer reconnecting */
eventfd_write(vduse_queue_get_fd(vq), 1);
}
@@ -133,9 +149,14 @@ static void vduse_blk_enable_queue(VduseDev *dev,
VduseVirtq *vq)
static void vduse_blk_disable_queue(VduseDev *dev, VduseVirtq *vq)
{
VduseBlkExport *vblk_exp = vduse_dev_get_priv(dev);
+ int fd = vduse_queue_get_fd(vq);
- aio_set_fd_handler(vblk_exp->export.ctx, vduse_queue_get_fd(vq),
- true, NULL, NULL, NULL, NULL, NULL);
+ if (fd < 0) {
+ return;
+ }
+
+ aio_set_fd_handler(vblk_exp->export.ctx, fd, false,
+ NULL, NULL, NULL, NULL, NULL);
}
static const VduseOps vduse_blk_ops = {
@@ -152,42 +173,19 @@ static void on_vduse_dev_kick(void *opaque)
static void vduse_blk_attach_ctx(VduseBlkExport *vblk_exp, AioContext *ctx)
{
- int i;
-
aio_set_fd_handler(vblk_exp->export.ctx, vduse_dev_get_fd(vblk_exp->dev),
- true, on_vduse_dev_kick, NULL, NULL, NULL,
+ false, on_vduse_dev_kick, NULL, NULL, NULL,
vblk_exp->dev);
- for (i = 0; i < vblk_exp->num_queues; i++) {
- VduseVirtq *vq = vduse_dev_get_queue(vblk_exp->dev, i);
- int fd = vduse_queue_get_fd(vq);
-
- if (fd < 0) {
- continue;
- }
- aio_set_fd_handler(vblk_exp->export.ctx, fd, true,
- on_vduse_vq_kick, NULL, NULL, NULL, vq);
- }
+ /* Virtqueues are handled by vduse_blk_drained_end() */
}
static void vduse_blk_detach_ctx(VduseBlkExport *vblk_exp)
{
- int i;
-
- for (i = 0; i < vblk_exp->num_queues; i++) {
- VduseVirtq *vq = vduse_dev_get_queue(vblk_exp->dev, i);
- int fd = vduse_queue_get_fd(vq);
-
- if (fd < 0) {
- continue;
- }
- aio_set_fd_handler(vblk_exp->export.ctx, fd,
- true, NULL, NULL, NULL, NULL, NULL);
- }
aio_set_fd_handler(vblk_exp->export.ctx, vduse_dev_get_fd(vblk_exp->dev),
- true, NULL, NULL, NULL, NULL, NULL);
+ false, NULL, NULL, NULL, NULL, NULL);
- AIO_WAIT_WHILE(vblk_exp->export.ctx, vblk_exp->inflight > 0);
+ /* Virtqueues are handled by vduse_blk_drained_begin() */
}
@@ -220,8 +218,55 @@ static void vduse_blk_resize(void *opaque)
(char *)&config.capacity);
}
+static void vduse_blk_stop_virtqueues(VduseBlkExport *vblk_exp)
+{
+ for (uint16_t i = 0; i < vblk_exp->num_queues; i++) {
+ VduseVirtq *vq = vduse_dev_get_queue(vblk_exp->dev, i);
+ vduse_blk_disable_queue(vblk_exp->dev, vq);
+ }
+
+ vblk_exp->vqs_started = false;
+}
+
+static void vduse_blk_start_virtqueues(VduseBlkExport *vblk_exp)
+{
+ vblk_exp->vqs_started = true;
+
+ for (uint16_t i = 0; i < vblk_exp->num_queues; i++) {
+ VduseVirtq *vq = vduse_dev_get_queue(vblk_exp->dev, i);
+ vduse_blk_enable_queue(vblk_exp->dev, vq);
+ }
+}
+
+static void vduse_blk_drained_begin(void *opaque)
+{
+ BlockExport *exp = opaque;
+ VduseBlkExport *vblk_exp = container_of(exp, VduseBlkExport, export);
+
+ vduse_blk_stop_virtqueues(vblk_exp);
+}
+
+static void vduse_blk_drained_end(void *opaque)
+{
+ BlockExport *exp = opaque;
+ VduseBlkExport *vblk_exp = container_of(exp, VduseBlkExport, export);
+
+ vduse_blk_start_virtqueues(vblk_exp);
+}
+
+static bool vduse_blk_drained_poll(void *opaque)
+{
+ BlockExport *exp = opaque;
+ VduseBlkExport *vblk_exp = container_of(exp, VduseBlkExport, export);
+
+ return qatomic_read(&vblk_exp->inflight) > 0;
+}
+
static const BlockDevOps vduse_block_ops = {
- .resize_cb = vduse_blk_resize,
+ .resize_cb = vduse_blk_resize,
+ .drained_begin = vduse_blk_drained_begin,
+ .drained_end = vduse_blk_drained_end,
+ .drained_poll = vduse_blk_drained_poll,
};
static int vduse_blk_exp_create(BlockExport *exp, BlockExportOptions *opts,
@@ -268,6 +313,7 @@ static int vduse_blk_exp_create(BlockExport *exp,
BlockExportOptions *opts,
vblk_exp->handler.serial = g_strdup(vblk_opts->serial ?: "");
vblk_exp->handler.logical_block_size = logical_block_size;
vblk_exp->handler.writable = opts->writable;
+ vblk_exp->vqs_started = true;
config.capacity =
cpu_to_le64(blk_getlength(exp->blk) >> VIRTIO_BLK_SECTOR_BITS);
@@ -322,14 +368,20 @@ static int vduse_blk_exp_create(BlockExport *exp,
BlockExportOptions *opts,
vduse_dev_setup_queue(vblk_exp->dev, i, queue_size);
}
- aio_set_fd_handler(exp->ctx, vduse_dev_get_fd(vblk_exp->dev), true,
+ aio_set_fd_handler(exp->ctx, vduse_dev_get_fd(vblk_exp->dev), false,
on_vduse_dev_kick, NULL, NULL, NULL, vblk_exp->dev);
blk_add_aio_context_notifier(exp->blk, blk_aio_attached, blk_aio_detach,
vblk_exp);
-
blk_set_dev_ops(exp->blk, &vduse_block_ops, exp);
+ /*
+ * We handle draining ourselves using an in-flight counter and by disabling
+ * virtqueue fd handlers. Do not queue BlockBackend requests, they need to
+ * complete so the in-flight counter reaches zero.
+ */
+ blk_set_disable_request_queuing(exp->blk, true);
+
return 0;
err:
vduse_dev_destroy(vblk_exp->dev);
@@ -344,6 +396,9 @@ static void vduse_blk_exp_delete(BlockExport *exp)
VduseBlkExport *vblk_exp = container_of(exp, VduseBlkExport, export);
int ret;
+ assert(qatomic_read(&vblk_exp->inflight) == 0);
+
+ vduse_blk_detach_ctx(vblk_exp);
blk_remove_aio_context_notifier(exp->blk, blk_aio_attached, blk_aio_detach,
vblk_exp);
blk_set_dev_ops(exp->blk, NULL, NULL);
@@ -355,13 +410,12 @@ static void vduse_blk_exp_delete(BlockExport *exp)
g_free(vblk_exp->handler.serial);
}
+/* Called with exp->ctx acquired */
static void vduse_blk_exp_request_shutdown(BlockExport *exp)
{
VduseBlkExport *vblk_exp = container_of(exp, VduseBlkExport, export);
- aio_context_acquire(vblk_exp->export.ctx);
- vduse_blk_detach_ctx(vblk_exp);
- aio_context_acquire(vblk_exp->export.ctx);
+ vduse_blk_stop_virtqueues(vblk_exp);
}
const BlockExportDriver blk_exp_vduse_blk = {
--
2.39.2
