When we still have an AIOCB registered for DMA operations, we try to settle the respective operation by draining the BlockBackend associated with the IDE device.
However, this assumes that every DMA operation is associated with an increment of the BlockBackend’s in-flight counter (e.g. through some ongoing I/O operation), so that draining the BB until its in-flight counter reaches 0 will settle all DMA operations. That is not the case: For TRIM, the guest can issue a zero-length operation that will not result in any I/O operation forwarded to the BlockBackend, and also not increment the in-flight counter in any other way. In such a case, blk_drain() will be a no-op if no other operations are in flight. It is clear that if blk_drain() is a no-op, the value of s->bus->dma->aiocb will not change between checking it in the `if` condition and asserting that it is NULL after blk_drain(). The particular problem is that ide_issue_trim() creates a BH (ide_trim_bh_cb()) to settle the TRIM request: iocb->common.cb() is ide_dma_cb(), which will either create a new request, or find the transfer to be done and call ide_set_inactive(), which clears s->bus->dma->aiocb. Therefore, the blk_drain() must wait for ide_trim_bh_cb() to run, which currently it will not always do. To fix this issue, we increment the BlockBackend's in-flight counter when the TRIM operation begins (in ide_issue_trim(), when the ide_trim_bh_cb() BH is created) and decrement it when ide_trim_bh_cb() is done. Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2029980 Suggested-by: Paolo Bonzini <pbonz...@redhat.com> Signed-off-by: Hanna Reitz <hre...@redhat.com> --- v1: https://lists.nongnu.org/archive/html/qemu-block/2022-01/msg00024.html v2: - Increment BB’s in-flight counter while the BH is active so that blk_drain() will poll until the BH is done, as suggested by Paolo (No git-backport-diff, because this patch was basically completely rewritten, so it wouldn’t be worth it.) --- hw/ide/core.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/hw/ide/core.c b/hw/ide/core.c index e28f8aad61..15138225be 100644 --- a/hw/ide/core.c +++ b/hw/ide/core.c @@ -433,12 +433,16 @@ static const AIOCBInfo trim_aiocb_info = { static void ide_trim_bh_cb(void *opaque) { TrimAIOCB *iocb = opaque; + BlockBackend *blk = iocb->s->blk; iocb->common.cb(iocb->common.opaque, iocb->ret); qemu_bh_delete(iocb->bh); iocb->bh = NULL; qemu_aio_unref(iocb); + + /* Paired with an increment in ide_issue_trim() */ + blk_dec_in_flight(blk); } static void ide_issue_trim_cb(void *opaque, int ret) @@ -508,6 +512,9 @@ BlockAIOCB *ide_issue_trim( IDEState *s = opaque; TrimAIOCB *iocb; + /* Paired with a decrement in ide_trim_bh_cb() */ + blk_inc_in_flight(s->blk); + iocb = blk_aio_get(&trim_aiocb_info, s->blk, cb, cb_opaque); iocb->s = s; iocb->bh = qemu_bh_new(ide_trim_bh_cb, iocb); -- 2.34.1
