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authorTejun Heo <tj@kernel.org>2016-05-25 23:11:57 +0300
committerIngo Molnar <mingo@kernel.org>2016-06-03 13:06:11 +0300
commited8ebd1d514126c0e54fbdbd231427dc91c877c2 (patch)
treedc2ffc9e0c17ace6aaa11abe4e13cd7c04ba7f7c /include/linux/percpu-refcount.h
parent6e2814745c67ab422b86262b05e6f23a56f28aa3 (diff)
downloadlinux-ed8ebd1d514126c0e54fbdbd231427dc91c877c2.tar.xz
percpu, locking: Revert ("percpu: Replace smp_read_barrier_depends() with lockless_dereference()")
lockless_dereference() is planned to grow a sanity check to ensure that the input parameter is a pointer. __ref_is_percpu() passes in an unsinged long value which is a combination of a pointer and a flag. While it can be casted to a pointer lvalue, the casting looks messy and it's a special case anyway. Let's revert back to open-coding READ_ONCE() and explicit barrier. This doesn't cause any functional changes. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Paul McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Pranith Kumar <bobby.prani@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: kernel-team@fb.com Link: http://lkml.kernel.org/g/20160522185040.GA23664@p183.telecom.by Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/linux/percpu-refcount.h')
-rw-r--r--include/linux/percpu-refcount.h12
1 files changed, 5 insertions, 7 deletions
diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index 84f542df7ff5..1c7eec09e5eb 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -136,14 +136,12 @@ static inline bool __ref_is_percpu(struct percpu_ref *ref,
* used as a pointer. If the compiler generates a separate fetch
* when using it as a pointer, __PERCPU_REF_ATOMIC may be set in
* between contaminating the pointer value, meaning that
- * ACCESS_ONCE() is required when fetching it.
- *
- * Also, we need a data dependency barrier to be paired with
- * smp_store_release() in __percpu_ref_switch_to_percpu().
- *
- * Use lockless deref which contains both.
+ * READ_ONCE() is required when fetching it.
*/
- percpu_ptr = lockless_dereference(ref->percpu_count_ptr);
+ percpu_ptr = READ_ONCE(ref->percpu_count_ptr);
+
+ /* paired with smp_store_release() in __percpu_ref_switch_to_percpu() */
+ smp_read_barrier_depends();
/*
* Theoretically, the following could test just ATOMIC; however,