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block-backend: Queue requests while drained

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This fixes devices like IDE that can still start new requests from I/O
handlers in the CPU thread while the block backend is drained.

The basic assumption is that in a drain section, no new requests should
be allowed through a BlockBackend (blk_drained_begin/end don't exist,
we get drain sections only on the node level). However, there are two
special cases where requests should not be queued:

1. Block jobs: We already make sure that block jobs are paused in a
   drain section, so they won't start new requests. However, if the
   drain_begin is called on the job's BlockBackend first, it can happen
   that we deadlock because the job stays busy until it reaches a pause
   point - which it can't if its requests aren't processed any more.

   The proper solution here would be to make all requests through the
   job's filter node instead of using a BlockBackend. For now, just
   disabling request queuing on the job BlockBackend is simpler.

2. In test cases where making requests through bdrv_* would be
   cumbersome because we'd need a BdrvChild. As we already got the
   functionality to disable request queuing from 1., use it in tests,
   too, for convenience.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Kevin Wolf 2019-07-22 17:46:23 +02:00
parent d2da5e288a
commit cf3129323f
7 changed files with 59 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

53
block/block-backend.c
View file

@ -79,6 +79,9 @@ struct BlockBackend {
QLIST_HEAD(, BlockBackendAioNotifier) aio_notifiers;
int quiesce_counter;
CoQueue queued_requests;
bool disable_request_queuing;
VMChangeStateEntry *vmsh;
bool force_allow_inactivate;
@ -339,6 +342,7 @@ BlockBackend *blk_new(AioContext *ctx, uint64_t perm, uint64_t shared_perm)
block_acct_init(&blk->stats);
qemu_co_queue_init(&blk->queued_requests);
notifier_list_init(&blk->remove_bs_notifiers);
notifier_list_init(&blk->insert_bs_notifiers);
QLIST_INIT(&blk->aio_notifiers);
@ -1096,6 +1100,11 @@ void blk_set_allow_aio_context_change(BlockBackend *blk, bool allow)
blk->allow_aio_context_change = allow;
}
void blk_set_disable_request_queuing(BlockBackend *blk, bool disable)
{
blk->disable_request_queuing = disable;
}
static int blk_check_byte_request(BlockBackend *blk, int64_t offset,
size_t size)
{
@ -1127,13 +1136,24 @@ static int blk_check_byte_request(BlockBackend *blk, int64_t offset,
return 0;
}
static void coroutine_fn blk_wait_while_drained(BlockBackend *blk)
{
if (blk->quiesce_counter && !blk->disable_request_queuing) {
qemu_co_queue_wait(&blk->queued_requests, NULL);
}
}
int coroutine_fn blk_co_preadv(BlockBackend *blk, int64_t offset,
unsigned int bytes, QEMUIOVector *qiov,
BdrvRequestFlags flags)
{
int ret;
BlockDriverState *bs = blk_bs(blk);
BlockDriverState *bs;
blk_wait_while_drained(blk);
/* Call blk_bs() only after waiting, the graph may have changed */
bs = blk_bs(blk);
trace_blk_co_preadv(blk, bs, offset, bytes, flags);
ret = blk_check_byte_request(blk, offset, bytes);
@ -1159,8 +1179,12 @@ int coroutine_fn blk_co_pwritev(BlockBackend *blk, int64_t offset,
BdrvRequestFlags flags)
{
int ret;
BlockDriverState *bs = blk_bs(blk);
BlockDriverState *bs;
blk_wait_while_drained(blk);
/* Call blk_bs() only after waiting, the graph may have changed */
bs = blk_bs(blk);
trace_blk_co_pwritev(blk, bs, offset, bytes, flags);
ret = blk_check_byte_request(blk, offset, bytes);
@ -1349,6 +1373,12 @@ static void blk_aio_read_entry(void *opaque)
BlkRwCo *rwco = &acb->rwco;
QEMUIOVector *qiov = rwco->iobuf;
if (rwco->blk->quiesce_counter) {
blk_dec_in_flight(rwco->blk);
blk_wait_while_drained(rwco->blk);
blk_inc_in_flight(rwco->blk);
}
assert(qiov->size == acb->bytes);
rwco->ret = blk_co_preadv(rwco->blk, rwco->offset, acb->bytes,
qiov, rwco->flags);
@ -1361,6 +1391,12 @@ static void blk_aio_write_entry(void *opaque)
BlkRwCo *rwco = &acb->rwco;
QEMUIOVector *qiov = rwco->iobuf;
if (rwco->blk->quiesce_counter) {
blk_dec_in_flight(rwco->blk);
blk_wait_while_drained(rwco->blk);
blk_inc_in_flight(rwco->blk);
}
assert(!qiov || qiov->size == acb->bytes);
rwco->ret = blk_co_pwritev(rwco->blk, rwco->offset, acb->bytes,
qiov, rwco->flags);
@ -1482,6 +1518,8 @@ void blk_aio_cancel_async(BlockAIOCB *acb)
int blk_co_ioctl(BlockBackend *blk, unsigned long int req, void *buf)
{
blk_wait_while_drained(blk);
if (!blk_is_available(blk)) {
return -ENOMEDIUM;
}
@ -1522,7 +1560,11 @@ BlockAIOCB *blk_aio_ioctl(BlockBackend *blk, unsigned long int req, void *buf,
int blk_co_pdiscard(BlockBackend *blk, int64_t offset, int bytes)
{
int ret = blk_check_byte_request(blk, offset, bytes);
int ret;
blk_wait_while_drained(blk);
ret = blk_check_byte_request(blk, offset, bytes);
if (ret < 0) {
return ret;
}
@ -1532,6 +1574,8 @@ int blk_co_pdiscard(BlockBackend *blk, int64_t offset, int bytes)
int blk_co_flush(BlockBackend *blk)
{
blk_wait_while_drained(blk);
if (!blk_is_available(blk)) {
return -ENOMEDIUM;
}
@ -2232,6 +2276,9 @@ static void blk_root_drained_end(BdrvChild *child, int *drained_end_counter)
if (blk->dev_ops && blk->dev_ops->drained_end) {
blk->dev_ops->drained_end(blk->dev_opaque);
}
while (qemu_co_enter_next(&blk->queued_requests, NULL)) {
/* Resume all queued requests */
}
}
}