Re: SCSI EH wakeup deadlock from deferred_qc
Damien Le Moal <[email protected]> Thu, 9 Jul 2026 10:01:11 +0900
| Newsgroups | gmane.linux.ide |
|---|---|
| Organization | Western Digital Research |
| Message-ID | <[email protected]> |
On 7/9/26 08:44, Damien Le Moal wrote: > On 7/9/26 04:36, Igor Pylypiv wrote: >> Hi Damien, >> >> I've stumbled upon an issue where SCSI EH didn't run upon command timeout >> but ran ~10 or so seconds later. It seems like a recent regression from >> the introduction of deffered_qc. >> >> When an active command times out while a non-NCQ command is waiting in >> deferred_qc, SCSI EH fails to wake up. Recovery stalls until the deferred >> command's own timer expires. >> >> When an NCQ command times out, scsi_timeout() calls scsi_eh_scmd_add(), >> incrementing shost->host_failed (1). However, when scsi_eh_wakeup() checks >> whether to wake the EH thread, scsi_host_busy(shost) counts 2 active >> commands (1 timed-out + 1 in deferred_qc). >> >> Because busy (2) != host_failed (1), scsi_eh_wakeup() refuses to wake >> the EH thread, deadlocking error recovery until the deferred command >> times out on its own. > > Igor, > > Can you try the attached diff ? > I will test on my end, but I need to hack something to trigger a timeout :) Hacking libahci to trigger a timeout for a particular LBA read, I tested the attached v2 and I see the deferred QC running right after the read command timeout. So this looks like a good fix to me. Can you test please ? -- Damien Le Moal Western Digital Research
ata-timeout-v2.diff
(text/x-patch, 3.1 KB)
diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index 5868526301a2..5221d7004c0e 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -1685,7 +1685,8 @@ void ata_scsi_deferred_qc_work(struct work_struct *work)
spin_unlock_irqrestore(ap->lock, flags);
}
-void ata_scsi_requeue_deferred_qc(struct ata_port *ap)
+static void ata_scsi_do_requeue_deferred_qc(struct ata_port *ap,
+ struct scsi_cmnd *timed_out_scmd)
{
struct ata_link *link;
@@ -1698,15 +1699,27 @@ void ata_scsi_requeue_deferred_qc(struct ata_port *ap)
*/
ata_for_each_link(link, ap, PMP_FIRST) {
struct ata_queued_cmd *qc = link->deferred_qc;
+ u32 host_byte;
- if (qc) {
- link->deferred_qc = NULL;
- cancel_work(&link->deferred_qc_work);
- ata_scsi_qc_done(qc, true, DID_REQUEUE << 16);
- }
+ if (!qc)
+ continue;
+
+ link->deferred_qc = NULL;
+ cancel_work(&link->deferred_qc_work);
+
+ if (qc->scsicmd == timed_out_scmd)
+ host_byte = DID_TIME_OUT;
+ else
+ host_byte = DID_REQUEUE;
+ ata_scsi_qc_done(qc, true, host_byte << 16);
}
}
+void ata_scsi_requeue_deferred_qc(struct ata_port *ap)
+{
+ ata_scsi_do_requeue_deferred_qc(ap, NULL);
+}
+
static void ata_scsi_schedule_deferred_qc(struct ata_link *link)
{
struct ata_queued_cmd *qc = link->deferred_qc;
@@ -1730,6 +1743,28 @@ static void ata_scsi_schedule_deferred_qc(struct ata_link *link)
queue_work(system_highpri_wq, &link->deferred_qc_work);
}
+enum scsi_timeout_action ata_scsi_eh_timed_out(struct scsi_cmnd *scmd)
+{
+ struct ata_port *ap = ata_shost_to_port(scmd->device->host);
+ unsigned long flags;
+
+ /*
+ * We had a timeout, either for an NCQ command or for one deferred
+ * queued command. Either way, we must release all deferred queued
+ * command so that scsi EH can trigger.
+ */
+ spin_lock_irqsave(ap->lock, flags);
+ ata_scsi_do_requeue_deferred_qc(ap, scmd);
+ spin_unlock_irqrestore(ap->lock, flags);
+
+ /*
+ * Let scsi_timeout() know that it must continue with handling the
+ * timeout as we in fact did not do much here.
+ */
+ return SCSI_EH_NOT_HANDLED;
+}
+EXPORT_SYMBOL_GPL(ata_scsi_eh_timed_out);
+
static void ata_scsi_qc_complete(struct ata_queued_cmd *qc)
{
struct ata_link *link = qc->dev->link;
diff --git a/include/linux/libata.h b/include/linux/libata.h
index 96e626d6a7ca..327da43d7496 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -1153,6 +1153,7 @@ extern int ata_scsi_ioctl(struct scsi_device *dev, unsigned int cmd,
#endif
extern enum scsi_qc_status ata_scsi_queuecmd(struct Scsi_Host *h,
struct scsi_cmnd *cmd);
+enum scsi_timeout_action ata_scsi_eh_timed_out(struct scsi_cmnd *cmd);
#if IS_REACHABLE(CONFIG_ATA)
bool ata_scsi_dma_need_drain(struct request *rq);
#else
@@ -1464,6 +1465,7 @@ extern const struct attribute_group *ata_common_sdev_groups[];
.ioctl = ata_scsi_ioctl, \
ATA_SCSI_COMPAT_IOCTL \
.queuecommand = ata_scsi_queuecmd, \
+ .eh_timed_out = ata_scsi_eh_timed_out, \
.dma_need_drain = ata_scsi_dma_need_drain, \
.this_id = ATA_SHT_THIS_ID, \
.emulated = ATA_SHT_EMULATED, \