The patch below does not apply to the 4.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable@xxxxxxxxxxxxxxx>. thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 3bd6f43f5cb3714f70c591514f344389df593501 Mon Sep 17 00:00:00 2001 From: Bart Van Assche <bart.vanassche@xxxxxxx> Date: Mon, 4 Dec 2017 10:06:23 -0800 Subject: [PATCH] scsi: core: Ensure that the SCSI error handler gets woken up If scsi_eh_scmd_add() is called concurrently with scsi_host_queue_ready() while shost->host_blocked > 0 then it can happen that neither function wakes up the SCSI error handler. Fix this by making every function that decreases the host_busy counter wake up the error handler if necessary and by protecting the host_failed checks with the SCSI host lock. Reported-by: Pavel Tikhomirov <ptikhomirov@xxxxxxxxxxxxx> References: https://marc.info/?l=linux-kernel&m=150461610630736 Fixes: commit 746650160866 ("scsi: convert host_busy to atomic_t") Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxx> Reviewed-by: Pavel Tikhomirov <ptikhomirov@xxxxxxxxxxxxx> Tested-by: Stuart Hayes <stuart.w.hayes@xxxxxxxxx> Cc: Konstantin Khorenko <khorenko@xxxxxxxxxxxxx> Cc: Stuart Hayes <stuart.w.hayes@xxxxxxxxx> Cc: Pavel Tikhomirov <ptikhomirov@xxxxxxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxx> Cc: Hannes Reinecke <hare@xxxxxxxx> Cc: Johannes Thumshirn <jthumshirn@xxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx> diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c index fe3a0da3ec97..57bf43e34863 100644 --- a/drivers/scsi/hosts.c +++ b/drivers/scsi/hosts.c @@ -318,6 +318,9 @@ static void scsi_host_dev_release(struct device *dev) scsi_proc_hostdir_rm(shost->hostt); + /* Wait for functions invoked through call_rcu(&shost->rcu, ...) */ + rcu_barrier(); + if (shost->tmf_work_q) destroy_workqueue(shost->tmf_work_q); if (shost->ehandler) @@ -325,6 +328,8 @@ static void scsi_host_dev_release(struct device *dev) if (shost->work_q) destroy_workqueue(shost->work_q); + destroy_rcu_head(&shost->rcu); + if (shost->shost_state == SHOST_CREATED) { /* * Free the shost_dev device name here if scsi_host_alloc() @@ -399,6 +404,7 @@ struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize) INIT_LIST_HEAD(&shost->starved_list); init_waitqueue_head(&shost->host_wait); mutex_init(&shost->scan_mutex); + init_rcu_head(&shost->rcu); index = ida_simple_get(&host_index_ida, 0, 0, GFP_KERNEL); if (index < 0) diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c index 62b56de38ae8..3737c6d3b064 100644 --- a/drivers/scsi/scsi_error.c +++ b/drivers/scsi/scsi_error.c @@ -220,6 +220,17 @@ static void scsi_eh_reset(struct scsi_cmnd *scmd) } } +static void scsi_eh_inc_host_failed(struct rcu_head *head) +{ + struct Scsi_Host *shost = container_of(head, typeof(*shost), rcu); + unsigned long flags; + + spin_lock_irqsave(shost->host_lock, flags); + shost->host_failed++; + scsi_eh_wakeup(shost); + spin_unlock_irqrestore(shost->host_lock, flags); +} + /** * scsi_eh_scmd_add - add scsi cmd to error handling. * @scmd: scmd to run eh on. @@ -242,9 +253,12 @@ void scsi_eh_scmd_add(struct scsi_cmnd *scmd) scsi_eh_reset(scmd); list_add_tail(&scmd->eh_entry, &shost->eh_cmd_q); - shost->host_failed++; - scsi_eh_wakeup(shost); spin_unlock_irqrestore(shost->host_lock, flags); + /* + * Ensure that all tasks observe the host state change before the + * host_failed change. + */ + call_rcu(&shost->rcu, scsi_eh_inc_host_failed); } /** diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index 1cbc497e00bd..1827956b33c9 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -318,22 +318,39 @@ static void scsi_init_cmd_errh(struct scsi_cmnd *cmd) cmd->cmd_len = scsi_command_size(cmd->cmnd); } -void scsi_device_unbusy(struct scsi_device *sdev) +/* + * Decrement the host_busy counter and wake up the error handler if necessary. + * Avoid as follows that the error handler is not woken up if shost->host_busy + * == shost->host_failed: use call_rcu() in scsi_eh_scmd_add() in combination + * with an RCU read lock in this function to ensure that this function in its + * entirety either finishes before scsi_eh_scmd_add() increases the + * host_failed counter or that it notices the shost state change made by + * scsi_eh_scmd_add(). + */ +static void scsi_dec_host_busy(struct Scsi_Host *shost) { - struct Scsi_Host *shost = sdev->host; - struct scsi_target *starget = scsi_target(sdev); unsigned long flags; + rcu_read_lock(); atomic_dec(&shost->host_busy); - if (starget->can_queue > 0) - atomic_dec(&starget->target_busy); - - if (unlikely(scsi_host_in_recovery(shost) && - (shost->host_failed || shost->host_eh_scheduled))) { + if (unlikely(scsi_host_in_recovery(shost))) { spin_lock_irqsave(shost->host_lock, flags); - scsi_eh_wakeup(shost); + if (shost->host_failed || shost->host_eh_scheduled) + scsi_eh_wakeup(shost); spin_unlock_irqrestore(shost->host_lock, flags); } + rcu_read_unlock(); +} + +void scsi_device_unbusy(struct scsi_device *sdev) +{ + struct Scsi_Host *shost = sdev->host; + struct scsi_target *starget = scsi_target(sdev); + + scsi_dec_host_busy(shost); + + if (starget->can_queue > 0) + atomic_dec(&starget->target_busy); atomic_dec(&sdev->device_busy); } @@ -1532,7 +1549,7 @@ static inline int scsi_host_queue_ready(struct request_queue *q, list_add_tail(&sdev->starved_entry, &shost->starved_list); spin_unlock_irq(shost->host_lock); out_dec: - atomic_dec(&shost->host_busy); + scsi_dec_host_busy(shost); return 0; } @@ -2018,7 +2035,7 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx, return BLK_STS_OK; out_dec_host_busy: - atomic_dec(&shost->host_busy); + scsi_dec_host_busy(shost); out_dec_target_busy: if (scsi_target(sdev)->can_queue > 0) atomic_dec(&scsi_target(sdev)->target_busy); diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h index a8b7bf879ced..1a1df0d21ee3 100644 --- a/include/scsi/scsi_host.h +++ b/include/scsi/scsi_host.h @@ -571,6 +571,8 @@ struct Scsi_Host { struct blk_mq_tag_set tag_set; }; + struct rcu_head rcu; + atomic_t host_busy; /* commands actually active on low-level */ atomic_t host_blocked;