scsi: Avoid that .queuecommand() gets called for a blocked SCSI device [Linux 5.3]

This Linux kernel change "scsi: Avoid that .queuecommand() gets called for a blocked SCSI device" is included in the Linux 5.3 release. This change is authored by Bart Van Assche <bvanassche [at] acm.org> on Mon Jun 17 08:18:19 2019 -0700. The commit for this change in Linux stable tree is bbe9fb0 (patch).

scsi: Avoid that .queuecommand() gets called for a blocked SCSI device

Several SCSI transport and LLD drivers surround code that does not
tolerate concurrent calls of .queuecommand() with scsi_target_block() /
scsi_target_unblock(). These last two functions use
blk_mq_quiesce_queue() / blk_mq_unquiesce_queue() for scsi-mq request
queues to prevent concurrent .queuecommand() calls. However, that is
not sufficient to prevent .queuecommand() calls from scsi_send_eh_cmnd().
Hence surround the .queuecommand() call from the SCSI error handler with
code that avoids that .queuecommand() gets called in the blocked state.

Note: converting the .queuecommand() call in scsi_send_eh_cmnd() into
code that calls blk_get_request() + blk_execute_rq() is not an option
since scsi_send_eh_cmnd() must be able to make forward progress even
if all requests have been allocated.

Cc: Ming Lei <ming.lei@redhat.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

There are 30 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/scsi/scsi_error.c | 26 ++++++++++++++++++++++++--
 drivers/scsi/scsi_lib.c   |  4 ----
 2 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index f490994..9f16304 100644
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -1055,7 +1055,7 @@ static int scsi_send_eh_cmnd(struct scsi_cmnd *scmd, unsigned char *cmnd,
    struct scsi_device *sdev = scmd->device;
    struct Scsi_Host *shost = sdev->host;
    DECLARE_COMPLETION_ONSTACK(done);
-   unsigned long timeleft = timeout;
+   unsigned long timeleft = timeout, delay;
    struct scsi_eh_save ses;
    const unsigned long stall_for = msecs_to_jiffies(100);
    int rtn;
@@ -1066,7 +1066,29 @@ static int scsi_send_eh_cmnd(struct scsi_cmnd *scmd, unsigned char *cmnd,

    scsi_log_send(scmd);
    scmd->scsi_done = scsi_eh_done;
-   rtn = shost->hostt->queuecommand(shost, scmd);
+
+   /*
+    * Lock sdev->state_mutex to avoid that scsi_device_quiesce() can
+    * change the SCSI device state after we have examined it and before
+    * .queuecommand() is called.
+    */
+   mutex_lock(&sdev->state_mutex);
+   while (sdev->sdev_state == SDEV_BLOCK && timeleft > 0) {
+       mutex_unlock(&sdev->state_mutex);
+       SCSI_LOG_ERROR_RECOVERY(5, sdev_printk(KERN_DEBUG, sdev,
+           "%s: state %d <> %d\n", __func__, sdev->sdev_state,
+           SDEV_BLOCK));
+       delay = min(timeleft, stall_for);
+       timeleft -= delay;
+       msleep(jiffies_to_msecs(delay));
+       mutex_lock(&sdev->state_mutex);
+   }
+   if (sdev->sdev_state != SDEV_BLOCK)
+       rtn = shost->hostt->queuecommand(shost, scmd);
+   else
+       rtn = SCSI_MLQUEUE_DEVICE_BUSY;
+   mutex_unlock(&sdev->state_mutex);
+
    if (rtn) {
        if (timeleft > stall_for) {
            scsi_eh_restore_cmnd(scmd, &ses);
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index b1b1a1a..6c84edc 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -2616,10 +2616,6 @@ int scsi_internal_device_block_nowait(struct scsi_device *sdev)
  * a legal transition). When the device is in this state, command processing
  * is paused until the device leaves the SDEV_BLOCK state. See also
  * scsi_internal_device_unblock().
- *
- * To do: avoid that scsi_send_eh_cmnd() calls queuecommand() after
- * scsi_internal_device_block() has blocked a SCSI device and also
- * remove the rport mutex lock and unlock calls from srp_queuecommand().
  */
 static int scsi_internal_device_block(struct scsi_device *sdev)
 {

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