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@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> > 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/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;
--
Best regards, Tikhomirov Pavel
Software Developer, Virtuozzo.