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 <ptikhomi...@virtuozzo.com> Fixes: commit 746650160866 ("scsi: convert host_busy to atomic_t") Signed-off-by: Bart Van Assche <bart.vanass...@wdc.com> Cc: Konstantin Khorenko <khore...@virtuozzo.com> Cc: Stuart Hayes <stuart.w.ha...@gmail.com> Cc: Pavel Tikhomirov <ptikhomi...@virtuozzo.com> Cc: Christoph Hellwig <h...@lst.de> Cc: Hannes Reinecke <h...@suse.com> Cc: Johannes Thumshirn <jthumsh...@suse.de> Cc: <sta...@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);
-- Best regards, Tikhomirov Pavel Software Developer, Virtuozzo.
