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authorElena Reshetova <elena.reshetova@intel.com>2019-01-30 13:18:51 +0200
committerIngo Molnar <mingo@kernel.org>2019-02-04 09:03:31 +0100
commit47b8f3ab9c49daa824af848f9e02889662d8638f (patch)
treebd42ab897748eafaacdc5d0bb97256a678cee3d5 /lib
parent412f34a82ccf7dd52f6b197f6450a33f03342523 (diff)
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refcount_t: Add ACQUIRE ordering on success for dec(sub)_and_test() variants
This adds an smp_acquire__after_ctrl_dep() barrier on successful decrease of refcounter value from 1 to 0 for refcount_dec(sub)_and_test variants and therefore gives stronger memory ordering guarantees than prior versions of these functions. Co-developed-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Elena Reshetova <elena.reshetova@intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Andrea Parri <andrea.parri@amarulasolutions.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: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will.deacon@arm.com> Cc: dvyukov@google.com Cc: keescook@chromium.org Cc: stern@rowland.harvard.edu Link: https://lkml.kernel.org/r/1548847131-27854-2-git-send-email-elena.reshetova@intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'lib')
-rw-r--r--lib/refcount.c18
1 files changed, 13 insertions, 5 deletions
diff --git a/lib/refcount.c b/lib/refcount.c
index ebcf8cd49e05..6e904af0fb3e 100644
--- a/lib/refcount.c
+++ b/lib/refcount.c
@@ -33,6 +33,9 @@
* Note that the allocator is responsible for ordering things between free()
* and alloc().
*
+ * The decrements dec_and_test() and sub_and_test() also provide acquire
+ * ordering on success.
+ *
*/
#include <linux/mutex.h>
@@ -164,8 +167,8 @@ EXPORT_SYMBOL(refcount_inc_checked);
* at UINT_MAX.
*
* Provides release memory ordering, such that prior loads and stores are done
- * before, and provides a control dependency such that free() must come after.
- * See the comment on top.
+ * before, and provides an acquire ordering on success such that free()
+ * must come after.
*
* Use of this function is not recommended for the normal reference counting
* use case in which references are taken and released one at a time. In these
@@ -190,7 +193,12 @@ bool refcount_sub_and_test_checked(unsigned int i, refcount_t *r)
} while (!atomic_try_cmpxchg_release(&r->refs, &val, new));
- return !new;
+ if (!new) {
+ smp_acquire__after_ctrl_dep();
+ return true;
+ }
+ return false;
+
}
EXPORT_SYMBOL(refcount_sub_and_test_checked);
@@ -202,8 +210,8 @@ EXPORT_SYMBOL(refcount_sub_and_test_checked);
* decrement when saturated at UINT_MAX.
*
* Provides release memory ordering, such that prior loads and stores are done
- * before, and provides a control dependency such that free() must come after.
- * See the comment on top.
+ * before, and provides an acquire ordering on success such that free()
+ * must come after.
*
* Return: true if the resulting refcount is 0, false otherwise
*/