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block: add BlockBackend->in_flight counter

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BlockBackend currently relies on BlockDriverState->in_flight to track
requests for blk_drain().  There is a corner case where
BlockDriverState->in_flight cannot be used though: blk->root can be NULL
when there is no medium.  This results in a segfault when the NULL
pointer is dereferenced.

Introduce a BlockBackend->in_flight counter for aio requests so it works
even when blk->root == NULL.

Based on a patch by Kevin Wolf <kwolf@redhat.com>.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2018-02-16 16:50:13 +00:00 committed by Kevin Wolf
parent 7719f3c968
commit 33f2a75777
2 changed files with 54 additions and 8 deletions
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2
block.c
View file

@ -4713,7 +4713,7 @@ out:
AioContext *bdrv_get_aio_context(BlockDriverState *bs)
{
return bs->aio_context;
return bs ? bs->aio_context : qemu_get_aio_context();
}
AioWait *bdrv_get_aio_wait(BlockDriverState *bs)

60
block/block-backend.c
View file

@ -73,6 +73,14 @@ struct BlockBackend {
int quiesce_counter;
VMChangeStateEntry *vmsh;
bool force_allow_inactivate;
/* Number of in-flight aio requests. BlockDriverState also counts
* in-flight requests but aio requests can exist even when blk->root is
* NULL, so we cannot rely on its counter for that case.
* Accessed with atomic ops.
*/
unsigned int in_flight;
AioWait wait;
};
typedef struct BlockBackendAIOCB {
@ -1225,11 +1233,22 @@ int blk_make_zero(BlockBackend *blk, BdrvRequestFlags flags)
return bdrv_make_zero(blk->root, flags);
}
static void blk_inc_in_flight(BlockBackend *blk)
{
atomic_inc(&blk->in_flight);
}
static void blk_dec_in_flight(BlockBackend *blk)
{
atomic_dec(&blk->in_flight);
aio_wait_kick(&blk->wait);
}
static void error_callback_bh(void *opaque)
{
struct BlockBackendAIOCB *acb = opaque;
bdrv_dec_in_flight(acb->common.bs);
blk_dec_in_flight(acb->blk);
acb->common.cb(acb->common.opaque, acb->ret);
qemu_aio_unref(acb);
}
@ -1240,7 +1259,7 @@ BlockAIOCB *blk_abort_aio_request(BlockBackend *blk,
{
struct BlockBackendAIOCB *acb;
bdrv_inc_in_flight(blk_bs(blk));
blk_inc_in_flight(blk);
acb = blk_aio_get(&block_backend_aiocb_info, blk, cb, opaque);
acb->blk = blk;
acb->ret = ret;
@ -1263,7 +1282,7 @@ static const AIOCBInfo blk_aio_em_aiocb_info = {
static void blk_aio_complete(BlkAioEmAIOCB *acb)
{
if (acb->has_returned) {
bdrv_dec_in_flight(acb->common.bs);
blk_dec_in_flight(acb->rwco.blk);
acb->common.cb(acb->common.opaque, acb->rwco.ret);
qemu_aio_unref(acb);
}
@ -1284,7 +1303,7 @@ static BlockAIOCB *blk_aio_prwv(BlockBackend *blk, int64_t offset, int bytes,
BlkAioEmAIOCB *acb;
Coroutine *co;
bdrv_inc_in_flight(blk_bs(blk));
blk_inc_in_flight(blk);
acb = blk_aio_get(&blk_aio_em_aiocb_info, blk, cb, opaque);
acb->rwco = (BlkRwCo) {
.blk = blk,
@ -1521,14 +1540,41 @@ int blk_flush(BlockBackend *blk)
void blk_drain(BlockBackend *blk)
{
if (blk_bs(blk)) {
bdrv_drain(blk_bs(blk));
BlockDriverState *bs = blk_bs(blk);
if (bs) {
bdrv_drained_begin(bs);
}
/* We may have -ENOMEDIUM completions in flight */
AIO_WAIT_WHILE(&blk->wait,
blk_get_aio_context(blk),
atomic_mb_read(&blk->in_flight) > 0);
if (bs) {
bdrv_drained_end(bs);
}
}
void blk_drain_all(void)
{
bdrv_drain_all();
BlockBackend *blk = NULL;
bdrv_drain_all_begin();
while ((blk = blk_all_next(blk)) != NULL) {
AioContext *ctx = blk_get_aio_context(blk);
aio_context_acquire(ctx);
/* We may have -ENOMEDIUM completions in flight */
AIO_WAIT_WHILE(&blk->wait, ctx,
atomic_mb_read(&blk->in_flight) > 0);
aio_context_release(ctx);
}
bdrv_drain_all_end();
}
void blk_set_on_error(BlockBackend *blk, BlockdevOnError on_read_error,