James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> writes:
> On Thu, 2015-01-22 at 08:50 -0800, Christoph Hellwig wrote:
>> We'll also still need to change scsi_device_put to deal with
>> a negative refcount..
>
> I don't believe so ... we never call module_refcount() now, and the
> actual module ref count never goes negative. That's the point of
> Rusty's change. In the unload routines, the actual module refcount is
> zero. __module_get() will increment this and the final module_put()
> will decrement it without triggering a warning.
>
> In the old code, we expected try_module_get() to fail but then used
> module_refcount() to detect the failure and not do a put.
Yep, I've put that patch in my fixes queue now.
Thanks,
Rusty.
From: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Subject: scsi: always increment reference count
James reported:
> After e513cc1 module: Remove stop_machine from module unloading,
> module_refcount() is returning (unsigned long)-1 when called from within
> a routine that runs in module_exit. This is confusing the scsi device
> put code which is coded to detect a module_refcount() of zero for
> running within a module exit routine and not try to do another
> module_put. The fix is to restore the original behaviour of
> module_refcount() and return zero if we're running inside an exit
> routine.
The correct fix is to turn try_module_get() into __module_get(), and
always do the module_put().
Acked-by: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index e02885451425..9b3829931f40 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -986,9 +986,9 @@ int scsi_device_get(struct scsi_device *sdev)
return -ENXIO;
if (!get_device(&sdev->sdev_gendev))
return -ENXIO;
- /* We can fail this if we're doing SCSI operations
+ /* We can fail try_module_get if we're doing SCSI operations
* from module exit (like cache flush) */
- try_module_get(sdev->host->hostt->module);
+ __module_get(sdev->host->hostt->module);
return 0;
}
@@ -1004,14 +1004,7 @@ EXPORT_SYMBOL(scsi_device_get);
*/
void scsi_device_put(struct scsi_device *sdev)
{
-#ifdef CONFIG_MODULE_UNLOAD
- struct module *module = sdev->host->hostt->module;
-
- /* The module refcount will be zero if scsi_device_get()
- * was called from a module removal routine */
- if (module && module_refcount(module) != 0)
- module_put(module);
-#endif
+ module_put(sdev->host->hostt->module);
put_device(&sdev->sdev_gendev);
}
EXPORT_SYMBOL(scsi_device_put);
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