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block/export: rewrite vduse-blk drain code

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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 <stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230516190238.8401-14-stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2023-05-16 15:02:31 -04:00 committed by Kevin Wolf
parent fb5cba2c7e
commit 195332c1d9
1 changed files with 93 additions and 39 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

132
block/export/vduse-blk.c
View File

@ -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);
ret = vduse_dev_destroy(vblk_exp->dev);
@ -354,13 +409,12 @@ 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 = {