block: Start/end drain on correct AioContext
bdrv_parent_drained_{begin,end}_single() are supposed to operate on the parent, not on the child, so they should not attempt to get the context to poll from the child but the parent instead. BDRV_POLL_WHILE(c->bs) does get the context from the child, so we should replace it with AIO_WAIT_WHILE() on the parent's context instead. This problem becomes apparent when bdrv_replace_child_noperm() invokes bdrv_parent_drained_end_single() after removing a child from a subgraph that is in an I/O thread. By the time bdrv_parent_drained_end_single() is called, child->bs is NULL, and so BDRV_POLL_WHILE(c->bs, ...) will poll the main loop instead of the I/O thread; but anything that bdrv_parent_drained_end_single_no_poll() may have scheduled is going to want to run in the I/O thread, but because we poll the main loop, the I/O thread is never unpaused, and nothing is run, resulting in a deadlock. Closes: https://gitlab.com/qemu-project/qemu/-/issues/1215 Reviewed-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Hanna Reitz <hreitz@redhat.com> Message-Id: <20221107151321.211175-4-hreitz@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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@ -71,9 +71,10 @@ static void bdrv_parent_drained_end_single_no_poll(BdrvChild *c,
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void bdrv_parent_drained_end_single(BdrvChild *c)
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void bdrv_parent_drained_end_single(BdrvChild *c)
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{
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{
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int drained_end_counter = 0;
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int drained_end_counter = 0;
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AioContext *ctx = bdrv_child_get_parent_aio_context(c);
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IO_OR_GS_CODE();
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IO_OR_GS_CODE();
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bdrv_parent_drained_end_single_no_poll(c, &drained_end_counter);
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bdrv_parent_drained_end_single_no_poll(c, &drained_end_counter);
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BDRV_POLL_WHILE(c->bs, qatomic_read(&drained_end_counter) > 0);
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AIO_WAIT_WHILE(ctx, qatomic_read(&drained_end_counter) > 0);
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}
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}
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static void bdrv_parent_drained_end(BlockDriverState *bs, BdrvChild *ignore,
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static void bdrv_parent_drained_end(BlockDriverState *bs, BdrvChild *ignore,
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@ -116,13 +117,14 @@ static bool bdrv_parent_drained_poll(BlockDriverState *bs, BdrvChild *ignore,
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void bdrv_parent_drained_begin_single(BdrvChild *c, bool poll)
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void bdrv_parent_drained_begin_single(BdrvChild *c, bool poll)
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{
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{
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AioContext *ctx = bdrv_child_get_parent_aio_context(c);
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IO_OR_GS_CODE();
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IO_OR_GS_CODE();
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c->parent_quiesce_counter++;
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c->parent_quiesce_counter++;
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if (c->klass->drained_begin) {
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if (c->klass->drained_begin) {
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c->klass->drained_begin(c);
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c->klass->drained_begin(c);
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}
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}
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if (poll) {
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if (poll) {
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BDRV_POLL_WHILE(c->bs, bdrv_parent_drained_poll_single(c));
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AIO_WAIT_WHILE(ctx, bdrv_parent_drained_poll_single(c));
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}
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}
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}
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}
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