Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751580AbdFEJiR (ORCPT ); Mon, 5 Jun 2017 05:38:17 -0400 Received: from mail-pg0-f67.google.com ([74.125.83.67]:34029 "EHLO mail-pg0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751295AbdFEJiP (ORCPT ); Mon, 5 Jun 2017 05:38:15 -0400 From: Ganesh Mahendran To: jejb@linux.vnet.ibm.com, martin.petersen@oracle.com, bart.vanassche@sandisk.com, hch@lst.de Cc: linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, Ganesh Mahendran Subject: [PATCH] scsi_lib: increase {host|target|device}_busy count after dispatch cmd Date: Mon, 5 Jun 2017 17:37:58 +0800 Message-Id: <1496655478-4039-1-git-send-email-opensource.ganesh@gmail.com> X-Mailer: git-send-email 1.9.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6814 Lines: 232 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 --- 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