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@xxxxxxxxxxxxx>
Fixes: commit 746650160866 ("scsi: convert host_busy to atomic_t")
Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxx>
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>
---
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.