On 2017/11/30 1:39, Bart Van Assche wrote:
On Wed, 2017-11-29 at 17:20 +0100, hch@xxxxxx wrote:
On Wed, Nov 29, 2017 at 04:18:30PM +0000, Bart Van Assche wrote:
As the above patch description shows it can happen that the SCSI core calls
get_device() after the device reference count has reached zero and before
the memory for struct device is freed. Although the above patch looks fine
to me, would you consider it acceptable to modify get_device() such that it
uses kobject_get_unless_zero() instead of kobject_get()? I'm asking this
because that change would help to reduce the complexity of the already too
complicated SCSI core.
I don't think we can just modify get_device, but we can add a new
get_device_unless_zero. In fact I have an open coded variant of that
in nvme, and was planning to submit one for the current merge window..
Sorry but I don't see why we can't modify get_device()? Can you explain why
you think that something like the patch below is wrong?
Thanks,
Bart.
Hi Bart, I chose the approach in my patch because it has been used in
scsi_device_get() for years and been proved safe. I think using
kobject_get_unless_zero() is safe here and can fix this issue too. And
this approach is beneficial to all users.
[PATCH] Make it safe to use get_device() if the reference count is zero
---
drivers/base/core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/base/core.c b/drivers/base/core.c
index 110230d86527..049a5d9dba8a 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1916,7 +1916,7 @@ EXPORT_SYMBOL_GPL(device_register);
*/
struct device *get_device(struct device *dev)
{
- return dev ? kobj_to_dev(kobject_get(&dev->kobj)) : NULL;
+ return dev && kobject_get_unless_zero(&dev->kobj) ? dev : NULL;
}
EXPORT_SYMBOL_GPL(get_device);
