mm/vmstat.c: fix /proc/vmstat format for CONFIG_DEBUG_TLBFLUSH=y CONFIG_SMP=n

[thirdparty/linux.git] / lib / sbitmap.c

diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 5b382c1244ede33c14016142ac2d7fec4d0608da..155fe38756ecfda251f26fa8616a325dddd8d455 100644 (file)
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -591,6 +591,17 @@ EXPORT_SYMBOL_GPL(sbitmap_queue_wake_up);
 void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
                         unsigned int cpu)
 {
+       /*
+        * Once the clear bit is set, the bit may be allocated out.
+        *
+        * Orders READ/WRITE on the asssociated instance(such as request
+        * of blk_mq) by this bit for avoiding race with re-allocation,
+        * and its pair is the memory barrier implied in __sbitmap_get_word.
+        *
+        * One invariant is that the clear bit has to be zero when the bit
+        * is in use.
+        */
+       smp_mb__before_atomic();
        sbitmap_deferred_clear_bit(&sbq->sb, nr);
 
        /*