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| author | Tejun Heo <tj@kernel.org> | 2016-05-25 16:11:57 -0400 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2016-06-03 12:06:11 +0200 |
| commit | ed8ebd1d514126c0e54fbdbd231427dc91c877c2 (patch) | |
| tree | dc2ffc9e0c17ace6aaa11abe4e13cd7c04ba7f7c /include/linux/percpu-refcount.h | |
| parent | 6e2814745c67ab422b86262b05e6f23a56f28aa3 (diff) | |
| download | lwn-ed8ebd1d514126c0e54fbdbd231427dc91c877c2.tar.gz lwn-ed8ebd1d514126c0e54fbdbd231427dc91c877c2.zip | |
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.h | 12 |
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, |