scsi: ufs: Fix concurrency of error handler and other error recovery paths

Error recovery can be invoked from multiple code paths, including hibern8
enter/exit (from ufshcd_link_recovery), ufshcd_eh_host_reset_handler() and
eh_work scheduled from IRQ context. Ultimately, these paths are all trying
to invoke ufshcd_reset_and_restore() in either a synchronous or
asynchronous manner. This causes problems:

 - If link recovery happens during ungate work, ufshcd_hold() would be
   called recursively. Although commit 53c12d0e ("scsi: ufs: fix error
   recovery after the hibern8 exit failure") fixed a deadlock due to
   recursive calls of ufshcd_hold() by adding a check of eh_in_progress
   into ufshcd_hold, this check allows eh_work to run in parallel while
   link recovery is running.

 - Similar concurrency can also happen when error recovery is invoked from
   ufshcd_eh_host_reset_handler and ufshcd_link_recovery.

 - Concurrency can even happen between eh_works. eh_work, currently queued
   on system_wq, is allowed to have multiple instances running in parallel,
   but we don't have proper protection for that.

If any of above concurrency scenarios happen, error recovery would fail and
lead ufs device and host into bad states. To fix the concurrency problem,
this change queues eh_work on a single threaded workqueue and removes link
recovery calls from the hibern8 enter/exit path. In addition, make use of
eh_work in eh_host_reset_handler instead of calling
ufshcd_reset_and_restore. This unifies the UFS error recovery mechanism.

According to the UFSHCI JEDEC spec, hibern8 enter/exit error occurs when
the link is broken. This essentially applies to any power mode change
operations (since they all use PACP_PWR cmds in UniPro layer). So, if a
power mode change operation (including AH8 enter/exit) fails, mark link
state as UIC_LINK_BROKEN_STATE and schedule the eh_work.  In this case,
error handler needs to do a full reset and restore to recover the link back
to active. Before the link state is recovered to active,
ufshcd_uic_pwr_ctrl simply returns -ENOLINK to avoid more errors.

Link: https://lore.kernel.org/r/1596975355-39813-6-git-send-email-cang@codeaurora.orgReviewed-by: Bean Huo <beanhuo@micron.com>
Reviewed-by: Asutosh Das <asutoshd@codeaurora.org>
Signed-off-by: Can Guo <cang@codeaurora.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/ufs/ufs-sysfs.c

@@ -16,6 +16,7 @@ static const char *ufschd_uic_link_state_to_string(
 	case UIC_LINK_OFF_STATE:	return "OFF";
 	case UIC_LINK_ACTIVE_STATE:	return "ACTIVE";
 	case UIC_LINK_HIBERN8_STATE:	return "HIBERN8";
+	case UIC_LINK_BROKEN_STATE:	return "BROKEN";
 	default:			return "UNKNOWN";
 	}
 }

drivers/scsi/ufs/ufshcd.h

@@ -90,6 +90,7 @@ enum uic_link_state {
 	UIC_LINK_OFF_STATE	= 0, /* Link powered down or disabled */
 	UIC_LINK_ACTIVE_STATE	= 1, /* Link is in Fast/Slow/Sleep state */
 	UIC_LINK_HIBERN8_STATE	= 2, /* Link is in Hibernate state */
+	UIC_LINK_BROKEN_STATE	= 3, /* Link is in broken state */
 };
 
 #define ufshcd_is_link_off(hba) ((hba)->uic_link_state == UIC_LINK_OFF_STATE)
@@ -97,11 +98,15 @@ enum uic_link_state {
 				    UIC_LINK_ACTIVE_STATE)
 #define ufshcd_is_link_hibern8(hba) ((hba)->uic_link_state == \
 				    UIC_LINK_HIBERN8_STATE)
+#define ufshcd_is_link_broken(hba) ((hba)->uic_link_state == \
+				   UIC_LINK_BROKEN_STATE)
 #define ufshcd_set_link_off(hba) ((hba)->uic_link_state = UIC_LINK_OFF_STATE)
 #define ufshcd_set_link_active(hba) ((hba)->uic_link_state = \
 				    UIC_LINK_ACTIVE_STATE)
 #define ufshcd_set_link_hibern8(hba) ((hba)->uic_link_state = \
 				    UIC_LINK_HIBERN8_STATE)
+#define ufshcd_set_link_broken(hba) ((hba)->uic_link_state = \
+				    UIC_LINK_BROKEN_STATE)
 
 #define ufshcd_set_ufs_dev_active(h) \
 	((h)->curr_dev_pwr_mode = UFS_ACTIVE_PWR_MODE)
@@ -616,12 +621,14 @@ struct ufs_hba_variant_params {
  * @intr_mask: Interrupt Mask Bits
  * @ee_ctrl_mask: Exception event control mask
  * @is_powered: flag to check if HBA is powered
+ * @eh_wq: Workqueue that eh_work works on
  * @eh_work: Worker to handle UFS errors that require s/w attention
  * @eeh_work: Worker to handle exception events
  * @errors: HBA errors
  * @uic_error: UFS interconnect layer error status
  * @saved_err: sticky error mask
  * @saved_uic_err: sticky UIC error mask
+ * @force_reset: flag to force eh_work perform a full reset
  * @silence_err_logs: flag to silence error logs
  * @dev_cmd: ufs device management command information
  * @last_dme_cmd_tstamp: time stamp of the last completed DME command
@@ -710,6 +717,7 @@ struct ufs_hba {
 	bool is_powered;
 
 	/* Work Queues */
+	struct workqueue_struct *eh_wq;
 	struct work_struct eh_work;
 	struct work_struct eeh_work;
 
@@ -719,6 +727,7 @@ struct ufs_hba {
 	u32 saved_err;
 	u32 saved_uic_err;
 	struct ufs_stats ufs_stats;
+	bool force_reset;
 	bool silence_err_logs;
 
 	/* Device management request data */