Re: kern/60182: ld@virtio sometimes hangs up

["Tetsuya Isaki via gnats" <gnats-admin%NetBSD.org@localhost>]

The following reply was made to PR kern/60182; it has been noted by GNATS.

From: Tetsuya Isaki <isaki%pastel-flower.jp@localhost>
To: Taylor R Campbell <riastradh%NetBSD.org@localhost>, gnats-bugs%NetBSD.org@localhost,
	netbsd-bugs%NetBSD.org@localhost
Cc: thorpej%netbsd.org@localhost
Subject: Re: kern/60182: ld@virtio sometimes hangs up
Date: Fri, 10 Apr 2026 14:09:46 +0900

 At Wed, 8 Apr 2026 16:05:16 +0000,
 Taylor R Campbell wrote:
 > Can you please try the attached patch?
 
 Thank you for looking into it.
 
 (By the way, the patch had syntax errors.
  - virtio_vq_is_enqueued(vq)
  + virtio_vq_is_enqueued(vsc, vq)
 But it's trivial and doesn't matter.  I attached the correct one.)
 
 Let's get back to the main topic.
 It still hanged up.
 
 virtio_vq_is_enqueued() issues POSTREAD for vq->vq_used region
 ((mainly?) in order to invalidate the cache),
 But, on 68030, POSTREAD is nop (and PREREAD invalidates the cache).
 See _bus_dmamap_sync_30() in sys/arch/m68k/m68k/bus_dma.c .
 ---
 Tetsuya Isaki <isaki%pastel-flower.jp@localhost / isaki%NetBSD.org@localhost>
 
 --- sys/dev/pci/ld_virtio.c
 +++ sys/dev/pci/ld_virtio.c
 @@ -502,7 +502,8 @@ ld_virtio_info(struct ld_softc *ld, bool poll)
  	while (sc->sc_sync_use != SYNC_FREE) {
  		if (poll) {
  			mutex_exit(&sc->sc_sync_wait_lock);
 -			ld_virtio_vq_done(vq);
 +			if (virtio_vq_is_enqueued(vsc, vq))
 +				ld_virtio_vq_done(vq);
  			mutex_enter(&sc->sc_sync_wait_lock);
  			continue;
  		}
 @@ -568,7 +569,8 @@ done:
  	while (sc->sc_sync_use != SYNC_DONE) {
  		if (poll) {
  			mutex_exit(&sc->sc_sync_wait_lock);
 -			ld_virtio_vq_done(vq);
 +			if (virtio_vq_is_enqueued(vsc, vq))
 +				ld_virtio_vq_done(vq);
  			mutex_enter(&sc->sc_sync_wait_lock);
  			continue;
  		}
 @@ -777,7 +779,8 @@ ld_virtio_dump(struct ld_softc *ld, void *data, daddr_t blkno, int blkcnt)
  	r = virtio_enqueue_prep(vsc, vq, &slot);
  	if (r != 0) {
  		if (r == EAGAIN) { /* no free slot; dequeue first */
 -			delay(100);
 +			while (!virtio_vq_is_enqueued(vsc, vq))
 +				delay(100);
  			ld_virtio_vq_done(vq);
  			r = virtio_enqueue_prep(vsc, vq, &slot);
  			if (r != 0)
 @@ -830,6 +833,8 @@ ld_virtio_dump(struct ld_softc *ld, void *data, daddr_t blkno, int blkcnt)
  	for ( ; ; ) {
  		int dslot;
  
 +		while (!virtio_vq_is_enqueued(vsc, vq))
 +			continue;
  		r = virtio_dequeue(vsc, vq, &dslot, NULL);
  		if (r != 0)
  			continue;
 @@ -915,7 +920,8 @@ ld_virtio_flush(struct ld_softc *ld, bool poll)
  	while (sc->sc_sync_use != SYNC_FREE) {
  		if (poll) {
  			mutex_exit(&sc->sc_sync_wait_lock);
 -			ld_virtio_vq_done(vq);
 +			if (virtio_vq_is_enqueued(vsc, vq))
 +				ld_virtio_vq_done(vq);
  			mutex_enter(&sc->sc_sync_wait_lock);
  			continue;
  		}
 @@ -963,7 +969,8 @@ ld_virtio_flush(struct ld_softc *ld, bool poll)
  	while (sc->sc_sync_use != SYNC_DONE) {
  		if (poll) {
  			mutex_exit(&sc->sc_sync_wait_lock);
 -			ld_virtio_vq_done(vq);
 +			if (virtio_vq_is_enqueued(vsc, vq))
 +				ld_virtio_vq_done(vq);
  			mutex_enter(&sc->sc_sync_wait_lock);
  			continue;
  		}