In android system, when there are lots of threads running. Thread A
holding *host_busy* count is easily to be preempted, and if at the
same time, thread B set *host_blocked*, then all other threads will
be io blocked.
Below the detail:
1). Thread A calls scsi_request_fn() and it increases *host_busy*.
But soon it is preempted.
2). Thread B call scsi_request_fn(), and it got failure from
scsi_dispatch_cmd(). So it set *host_blocked*
3). All the io blocked...
4). Thread A is scheduled again, and it decreases *host_busy*
in scsi_device_unbusy()
Afer step 2), all the io will be blocked, since scsi_host_queue_ready()
will always return 0.
----
scsi_host_queue_ready
{
if (atomic_read(&shost->host_blocked) > 0) {
if (busy) ==> true after step 2
goto starved;
}
----
The system will be unblocked after step 4).
This patch increases {host|target|device}_busy count after dispatch cmd.
Signed-off-by: Ganesh Mahendran <opensource.ganesh@xxxxxxxxx>
---
drivers/scsi/scsi_lib.c | 66 ++++++++++++++++++++++++-------------------------
1 file changed, 32 insertions(+), 34 deletions(-)
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 884aaa8..9cac272 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -311,6 +311,16 @@ static void scsi_init_cmd_errh(struct scsi_cmnd *cmd)
cmd->cmd_len = scsi_command_size(cmd->cmnd);
}
+static void scsi_device_busy(struct scsi_device *sdev)
+{
+ struct Scsi_Host *shost = sdev->host;
+ struct scsi_target *starget = scsi_target(sdev);
+
+ atomic_inc(&sdev->device_busy);
+ atomic_inc(&shost->host_busy);
+ atomic_inc(&starget->target_busy);
+}
+
void scsi_device_unbusy(struct scsi_device *sdev)
{
struct Scsi_Host *shost = sdev->host;
@@ -1352,12 +1362,13 @@ static void scsi_unprep_fn(struct request_queue *q, struct request *req)
static inline int scsi_dev_queue_ready(struct request_queue *q,
struct scsi_device *sdev)
{
+ int ret = 0;
unsigned int busy;
- busy = atomic_inc_return(&sdev->device_busy) - 1;
+ busy = atomic_read(&sdev->device_busy);
if (atomic_read(&sdev->device_blocked)) {
if (busy)
- goto out_dec;
+ goto out;
/*
* unblock after device_blocked iterates to zero
@@ -1368,19 +1379,18 @@ static inline int scsi_dev_queue_ready(struct request_queue *q,
*/
if (!q->mq_ops)
blk_delay_queue(q, SCSI_QUEUE_DELAY);
- goto out_dec;
+ goto out;
}
SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev,
"unblocking device at zero depth\n"));
}
if (busy >= sdev->queue_depth)
- goto out_dec;
+ goto out;
- return 1;
-out_dec:
- atomic_dec(&sdev->device_busy);
- return 0;
+ ret = 1;
+out:
+ return ret;
}
/*
@@ -1407,7 +1417,7 @@ static inline int scsi_target_queue_ready(struct Scsi_Host *shost,
if (starget->can_queue <= 0)
return 1;
- busy = atomic_inc_return(&starget->target_busy) - 1;
+ busy = atomic_read(&starget->target_busy);
if (atomic_read(&starget->target_blocked) > 0) {
if (busy)
goto starved;
@@ -1416,7 +1426,7 @@ static inline int scsi_target_queue_ready(struct Scsi_Host *shost,
* unblock after target_blocked iterates to zero
*/
if (atomic_dec_return(&starget->target_blocked) > 0)
- goto out_dec;
+ goto out;
SCSI_LOG_MLQUEUE(3, starget_printk(KERN_INFO, starget,
"unblocking target at zero depth\n"));
@@ -1431,9 +1441,7 @@ static inline int scsi_target_queue_ready(struct Scsi_Host *shost,
spin_lock_irq(shost->host_lock);
list_move_tail(&sdev->starved_entry, &shost->starved_list);
spin_unlock_irq(shost->host_lock);
-out_dec:
- if (starget->can_queue > 0)
- atomic_dec(&starget->target_busy);
+out:
return 0;
}
@@ -1451,7 +1459,7 @@ static inline int scsi_host_queue_ready(struct request_queue *q,
if (scsi_host_in_recovery(shost))
return 0;
- busy = atomic_inc_return(&shost->host_busy) - 1;
+ busy = atomic_read(&shost->host_busy);
if (atomic_read(&shost->host_blocked) > 0) {
if (busy)
goto starved;
@@ -1460,7 +1468,7 @@ static inline int scsi_host_queue_ready(struct request_queue *q,
* unblock after host_blocked iterates to zero
*/
if (atomic_dec_return(&shost->host_blocked) > 0)
- goto out_dec;
+ goto out;
SCSI_LOG_MLQUEUE(3,
shost_printk(KERN_INFO, shost,
@@ -1487,8 +1495,7 @@ static inline int scsi_host_queue_ready(struct request_queue *q,
if (list_empty(&sdev->starved_entry))
list_add_tail(&sdev->starved_entry, &shost->starved_list);
spin_unlock_irq(shost->host_lock);
-out_dec:
- atomic_dec(&shost->host_busy);
+out:
return 0;
}
@@ -1781,7 +1788,7 @@ static void scsi_request_fn(struct request_queue *q)
goto not_ready;
if (!scsi_host_queue_ready(q, shost, sdev))
- goto host_not_ready;
+ goto not_ready;
if (sdev->simple_tags)
cmd->flags |= SCMD_TAGGED;
@@ -1800,18 +1807,16 @@ static void scsi_request_fn(struct request_queue *q)
cmd->scsi_done = scsi_done;
rtn = scsi_dispatch_cmd(cmd);
if (rtn) {
- scsi_queue_insert(cmd, rtn);
+ __scsi_queue_insert(cmd, rtn, 0);
spin_lock_irq(q->queue_lock);
goto out_delay;
}
+ scsi_device_busy(sdev);
spin_lock_irq(q->queue_lock);
}
return;
- host_not_ready:
- if (scsi_target(sdev)->can_queue > 0)
- atomic_dec(&scsi_target(sdev)->target_busy);
not_ready:
/*
* lock q, handle tag, requeue req, and decrement device_busy. We
@@ -1823,7 +1828,6 @@ static void scsi_request_fn(struct request_queue *q)
*/
spin_lock_irq(q->queue_lock);
blk_requeue_request(q, req);
- atomic_dec(&sdev->device_busy);
out_delay:
if (!atomic_read(&sdev->device_busy) && !scsi_device_blocked(sdev))
blk_delay_queue(q, SCSI_QUEUE_DELAY);
@@ -1931,14 +1935,14 @@ static int scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
if (!scsi_dev_queue_ready(q, sdev))
goto out_put_device;
if (!scsi_target_queue_ready(shost, sdev))
- goto out_dec_device_busy;
+ goto out_put_device;
if (!scsi_host_queue_ready(q, shost, sdev))
- goto out_dec_target_busy;
+ goto out_put_device;
if (!(req->rq_flags & RQF_DONTPREP)) {
ret = prep_to_mq(scsi_mq_prep_fn(req));
if (ret != BLK_MQ_RQ_QUEUE_OK)
- goto out_dec_host_busy;
+ goto out_put_device;
req->rq_flags |= RQF_DONTPREP;
} else {
blk_mq_start_request(req);
@@ -1956,18 +1960,12 @@ static int scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
if (reason) {
scsi_set_blocked(cmd, reason);
ret = BLK_MQ_RQ_QUEUE_BUSY;
- goto out_dec_host_busy;
+ goto out_put_device;
}
+ scsi_device_busy(sdev);
return BLK_MQ_RQ_QUEUE_OK;
-out_dec_host_busy:
- atomic_dec(&shost->host_busy);
-out_dec_target_busy:
- if (scsi_target(sdev)->can_queue > 0)
- atomic_dec(&scsi_target(sdev)->target_busy);
-out_dec_device_busy:
- atomic_dec(&sdev->device_busy);
out_put_device:
put_device(&sdev->sdev_gendev);
out:
--
1.9.1
