scsi: fix the {host,target,device}_blocked counter mess
Seems like these counters are missing any sort of synchronization for
updates, as a over 10 year old comment from me noted. Fix this by
using atomic counters, and while we're at it also make sure they are
in the same cacheline as the _busy counters and not needlessly stored
to in every I/O completion.
With the new model the _busy counters can temporarily go negative,
so all the readers are updated to check for > 0 values. Longer
term every successful I/O completion will reset the counters to zero,
so the temporarily negative values will not cause any harm.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Webb Scales <webbnh@hp.com>
Acked-by: Jens Axboe <axboe@kernel.dk>
Tested-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Robert Elliott <elliott@hp.com>
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index 3329901..0f853f2 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -82,6 +82,8 @@
struct list_head same_target_siblings; /* just the devices sharing same target id */
atomic_t device_busy; /* commands actually active on LLDD */
+ atomic_t device_blocked; /* Device returned QUEUE_FULL. */
+
spinlock_t list_lock;
struct list_head cmd_list; /* queue of in use SCSI Command structures */
struct list_head starved_entry;
@@ -180,8 +182,6 @@
struct list_head event_list; /* asserted events */
struct work_struct event_work;
- unsigned int device_blocked; /* Device returned QUEUE_FULL. */
-
unsigned int max_device_blocked; /* what device_blocked counts down from */
#define SCSI_DEFAULT_DEVICE_BLOCKED 3
@@ -291,12 +291,13 @@
* the same target will also. */
/* commands actually active on LLD. */
atomic_t target_busy;
+ atomic_t target_blocked;
+
/*
* LLDs should set this in the slave_alloc host template callout.
* If set to zero then there is not limit.
*/
unsigned int can_queue;
- unsigned int target_blocked;
unsigned int max_target_blocked;
#define SCSI_DEFAULT_TARGET_BLOCKED 3
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 51f7911..5e8ebc1 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -583,6 +583,8 @@
struct blk_queue_tag *bqt;
atomic_t host_busy; /* commands actually active on low-level */
+ atomic_t host_blocked;
+
unsigned int host_failed; /* commands that failed.
protected by host_lock */
unsigned int host_eh_scheduled; /* EH scheduled without command */
@@ -682,11 +684,6 @@
struct workqueue_struct *tmf_work_q;
/*
- * Host has rejected a command because it was busy.
- */
- unsigned int host_blocked;
-
- /*
* Value host_blocked counts down from
*/
unsigned int max_host_blocked;
