On 05/23/2014 01:28 PM, Paolo Bonzini wrote:
Il 23/05/2014 12:37, Bart Van Assche ha scritto:
On 05/23/14 11:24, Paolo Bonzini wrote:
Il 23/05/2014 08:09, Hannes Reinecke ha scritto:
And when freeing a command we absolutely need to make sure that
the workqueue is empty.
So calling cancel_delayed_work() was the obvious thing to do.
You would need cancel_delayed_work_sync, but if it really
happened that
the work item is running, it would cause a double free.
I'd be fine with adding a WARN_ON(!list_empty(&cmd->abort_work))
here, however. This will clear up the intent of this statement.
BUG_ON even, since you'd get badness from the double free anyway.
Hello Paolo,
Are you aware that Linus strongly prefers WARN_ON_ONCE() over
BUG_ON() ?
See e.g. https://lkml.org/lkml/2012/9/27/461 or
https://lkml.org/lkml/2014/4/28/657.
Yes, I am and I even downgraded some KVM BUG_ONs recently.
But in this case I think that memory corruption is going to happen
anyway unless you consciously leak the Scsi_Cmnd * (because if you
use WARN_ON, you also need to return early as Linus suggested in the
second email).
So the WARN_ON/BUG_ON choice here should not just consider what
makes the problem easier to debug; hanging the machine before
guaranteed badness seems to me like a good use for BUG_ON.
So this should work, right?
diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index 88d46fe..53b8b94 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -334,7 +334,7 @@ void scsi_put_command(struct scsi_cmnd *cmd)
list_del_init(&cmd->list);
spin_unlock_irqrestore(&cmd->device->list_lock, flags);
- cancel_delayed_work(&cmd->abort_work);
+ BUG_ON(delayed_work_pending(&cmd->abort_work));
__scsi_put_command(cmd->device->host, cmd);
}
Cheers,
Hannes
--
Dr. Hannes Reinecke zSeries & Storage
hare@xxxxxxx +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
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