On 12/04/2017 09:06 PM, Bart Van Assche wrote:

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@virtuozzo.com 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@wdc.com > Cc: Konstantin Khorenko khorenko@virtuozzo.com Cc: Stuart Hayes stuart.w.hayes@gmail.com Cc: Pavel Tikhomirov ptikhomirov@virtuozzo.com Cc: Christoph Hellwig hch@lst.de Cc: Hannes Reinecke hare@suse.com Cc: Johannes Thumshirn jthumshirn@suse.de Cc: stable@vger.kernel.org

---

drivers/scsi/hosts.c | 6 ++++++ drivers/scsi/scsi_error.c | 18 ++++++++++++++++-- drivers/scsi/scsi_lib.c | 39 ++++++++++++++++++++++++++++----------- include/scsi/scsi_host.h | 2 ++ 4 files changed, 52 insertions(+), 13 deletions(-)

diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c index a306af6a5ea7..a0a7e4ff255c 100644 --- a/drivers/scsi/hosts.c +++ b/drivers/scsi/hosts.c @@ -324,6 +324,9 @@ 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)

@@ -331,6 +334,8 @@ 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 5e89049e9b4e..258b8a741992 100644 --- a/drivers/scsi/scsi_error.c +++ b/drivers/scsi/scsi_error.c @@ -226,6 +226,17 @@ 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++;

May be we need to increment host_failed before call_rcu(), so that all rcu protected readers already see a change at these point?

• 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.

@@ -248,9 +259,12 @@ 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 b6d3842b6809..5cbc69b2b1ae 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); } @@ -1531,7 +1548,7 @@ 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; }

@@ -2017,7 +2034,7 @@ 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;