[dm-devel] [PATCH 1/1]: missing call to pg_init_done causes I/O to be hung forever

[Menny_Hamburger at Dell.com]

When scsi_dh_activate returns SCSI_DH_NOSYS the H/W handler callback is not called, pg_init_done is not called in
the multipath layer and pending I/O is requeued forever; this situation causes all userland processes currently performing I/O
on the device to I/O hang. A similar situation occurs when the device has transitioned to SDEV_CANCEL/SDEV_DEL and the device
handler data had not yet been deleted.

The easiest way to reproduce this is in an ISCSI environment:
  dd if=/dev/dm-0 of=/dev/zero bs=8k count=1000000 &
  /etc/init.d/iscsi stop
In this example, dd will I/O hang forever and the only way to release it will be to reboot the machine

This patch calls pg_init_done directly from the mpath code when the scsi_dh_activate returns a non SCSI_DH_OK error.

Note:
The patch is over RHEL5.5.
When running an upstream kernel, the above scenario may not occur because the request queue is aborted in dm-mpath.c:fail_path.
This patch makes sure the problem does not occur at all, rather than handling it when it does. In addition, it seems too risky to apply
request queue abort functionality on RHEL5 at this stage.

diff -r -U 2 a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
--- a/drivers/md/dm-mpath.c   2010-12-13 09:16:31.358858000 +0200
+++ b/drivers/md/dm-mpath.c   2010-12-13 09:16:31.796998000 +0200
@@ -1190,4 +1190,5 @@
      case SCSI_DH_OK:
            break;
+     case SCSI_DH_DEV_OFFLINED:
      case SCSI_DH_NOSYS:
            if (!m->hw_handler_name) {
@@ -1252,7 +1253,15 @@
 {
      struct pgpath *pgpath = (struct pgpath *) data;
+     int err;

-     scsi_dh_activate(bdev_get_queue(pgpath->path.dev->bdev),
+     err = scsi_dh_activate(bdev_get_queue(pgpath->path.dev->bdev),
                        pg_init_done, &pgpath->path);
+
+     /*
+     * If error is not SCSI_DH_OK, we have not entered the scsi_dh H/W handler and did not call pg_init_done -
+     * need to call pg_init_done directly.
+     */
+     if (err)
+           pg_init_done(&pgpath->path, err);
 }

diff -r -U 2 a/drivers/scsi/device_handler/scsi_dh.c b/drivers/scsi/device_handler/scsi_dh.c
--- a/drivers/scsi/device_handler/scsi_dh.c     2010-12-13 09:16:31.616554000 +0200
+++ b/drivers/scsi/device_handler/scsi_dh.c     2010-12-13 09:16:31.878170000 +0200
@@ -443,4 +443,9 @@
      spin_unlock_irqrestore(q->queue_lock, flags);

+     if (sdev->sdev_state == SDEV_CANCEL ||
+         sdev->sdev_state == SDEV_DEL ||
+         sdev->sdev_state == SDEV_OFFLINE)
+           err = SCSI_DH_DEV_OFFLINED;
+
      if (err)
            return err;
diff -r -U 2 a/drivers/scsi/device_handler/scsi_dh_rdac.c b/drivers/scsi/device_handler/scsi_dh_rdac.c
--- a/drivers/scsi/device_handler/scsi_dh_rdac.c      2010-12-13 09:16:31.747755000 +0200
+++ b/drivers/scsi/device_handler/scsi_dh_rdac.c      2010-12-13 09:16:31.912827000 +0200
@@ -665,4 +665,5 @@
      if (fn)
            fn(data, err);
+
      return 0;
 }



Menny Hamburger
Engineer
Dell | IDC
office +972 97698789,  fax +972 97698889
Dell IDC. 4 Hacharoshet St, Raanana 43657, Israel

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