On 12/01/2017 01:44 AM, 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 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/scsi_error.c | 8 +++++++- drivers/scsi/scsi_lib.c | 39 ++++++++++++++++++++++++++++----------- 2 files changed, 35 insertions(+), 12 deletions(-)

diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c index 5e89049e9b4e..b22a9a23c74c 100644 --- a/drivers/scsi/scsi_error.c +++ b/drivers/scsi/scsi_error.c @@ -233,19 +233,25 @@ static void scsi_eh_reset(struct scsi_cmnd *scmd) void scsi_eh_scmd_add(struct scsi_cmnd *scmd) { struct Scsi_Host *shost = scmd->device->host;

• enum scsi_host_state shost_state; unsigned long flags; int ret;

WARN_ON_ONCE(!shost->ehandler); spin_lock_irqsave(shost->host_lock, flags);

• shost_state = shost->shost_state; if (scsi_host_set_state(shost, SHOST_RECOVERY)) { ret = scsi_host_set_state(shost, SHOST_CANCEL_RECOVERY); WARN_ON_ONCE(ret); } if (shost->eh_deadline != -1 && !shost->last_reset) shost->last_reset = jiffies;

• if (shost_state != shost->shost_state) {

• spin_unlock_irqrestore(shost->host_lock, flags);
  

• synchronize_rcu();
  

We can come here from interrupt context, so may be we should use call_rcu() here instead, possible backtrace:

=> scsi_eh_scmd_add => scsi_times_out => blk_rq_timed_out => blk_abort_request => ata_qc_schedule_eh => ata_qc_complete => ata_do_link_abort => ata_port_abort => ahci_handle_port_interrupt => ahci_single_irq_intr => __handle_irq_event_percpu => handle_irq_event_percpu => handle_irq_event => handle_edge_irq => handle_irq => do_IRQ

• spin_lock_irqsave(shost->host_lock, flags);
  

• } scsi_eh_reset(scmd); list_add_tail(&scmd->eh_entry, &shost->eh_cmd_q); shost->host_failed++;

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index b6d3842b6809..7d18fb245d7d 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 synchronize_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);