Re: [PATCH 01/18] drivers core: Add I/O ASID allocator

Paul E. McKenney
2019-04-09T14:53:08Z

On Tue, Apr 09, 2019 at 01:30:30PM +0300, Andriy Shevchenko wrote:
> On Tue, Apr 09, 2019 at 03:04:36AM -0700, Christoph Hellwig wrote:
> > On Tue, Apr 09, 2019 at 01:00:49PM +0300, Andriy Shevchenko wrote:
> > > I think it makes sense to add a helper macro to rcupdate.h
> > > (and we have several cases in kernel that can utilize it)
> > >
> > > #define kfree_non_null_rcu(ptr, rcu_head) \
> > > do { \
> > > if (ptr) \
> > > kfree_rcu(ptr, rcu_head); \
> > > } while (0)
> > >
> > > as a more common pattern for resource deallocators.
> >
> > I think that should move straight into kfree_rcu.
>
> Possible. I didn't dare to offer this due to lack of knowledge how it's used in
> other places.
>
> > In general
> > we expect *free* to deal with NULL pointers transparently, so we
> > should do so here as well.
>
> Exactly my point, thanks.

As shown below?

And now that you mention it, it is a bit surprising that no one has
complained before. ;-)

Thanx, Paul

------------------------------------------------------------------------

commit 23ad938244968e9d2a8001a1c52887c113b182f6
Author: Paul E. McKenney <paulmck@linux.ibm.com>
Date: Tue Apr 9 07:48:18 2019 -0700

rcu: Make kfree_rcu() ignore NULL pointers

This commit makes the kfree_rcu() macro's semantics be consistent
with the likes of kfree() by adding a check for NULL pointers, so
that kfree_rcu(NULL, ...) is a no-op.

Reported-by: Andriy Shevchenko <andriy.shevchenko@linux.intel.com>
Reported-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 922bb6848813..c68649b9bcec 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -828,9 +828,13 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
* The BUILD_BUG_ON check must not involve any function calls, hence the
* checks are done in macros here.
*/
-#define kfree_rcu(ptr, rcu_head) \
- __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
-
+#define kfree_rcu(ptr, rhf) \
+do { \
+ typeof (ptr) ___p = (ptr); \
+ \
+ if (___p) \
+ __kfree_rcu(&((___p)->rhf), offsetof(typeof(*(ptr)), rhf)); \
+} while (0)

/*
* Place this after a lock-acquisition primitive to guarantee that