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-rw-r--r--mm/slub.c37
1 files changed, 24 insertions, 13 deletions
diff --git a/mm/slub.c b/mm/slub.c
index fe376fe1f4fe..8b8508adf9c2 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2398,13 +2398,24 @@ redo:
* reading from one cpu area. That does not matter as long
* as we end up on the original cpu again when doing the cmpxchg.
*
- * Preemption is disabled for the retrieval of the tid because that
- * must occur from the current processor. We cannot allow rescheduling
- * on a different processor between the determination of the pointer
- * and the retrieval of the tid.
+ * We should guarantee that tid and kmem_cache are retrieved on
+ * the same cpu. It could be different if CONFIG_PREEMPT so we need
+ * to check if it is matched or not.
*/
- preempt_disable();
- c = this_cpu_ptr(s->cpu_slab);
+ do {
+ tid = this_cpu_read(s->cpu_slab->tid);
+ c = raw_cpu_ptr(s->cpu_slab);
+ } while (IS_ENABLED(CONFIG_PREEMPT) && unlikely(tid != c->tid));
+
+ /*
+ * Irqless object alloc/free algorithm used here depends on sequence
+ * of fetching cpu_slab's data. tid should be fetched before anything
+ * on c to guarantee that object and page associated with previous tid
+ * won't be used with current tid. If we fetch tid first, object and
+ * page could be one associated with next tid and our alloc/free
+ * request will be failed. In this case, we will retry. So, no problem.
+ */
+ barrier();
/*
* The transaction ids are globally unique per cpu and per operation on
@@ -2412,8 +2423,6 @@ redo:
* occurs on the right processor and that there was no operation on the
* linked list in between.
*/
- tid = c->tid;
- preempt_enable();
object = c->freelist;
page = c->page;
@@ -2512,7 +2521,7 @@ EXPORT_SYMBOL(kmem_cache_alloc_node_trace);
#endif
/*
- * Slow patch handling. This may still be called frequently since objects
+ * Slow path handling. This may still be called frequently since objects
* have a longer lifetime than the cpu slabs in most processing loads.
*
* So we still attempt to reduce cache line usage. Just take the slab
@@ -2659,11 +2668,13 @@ redo:
* data is retrieved via this pointer. If we are on the same cpu
* during the cmpxchg then the free will succedd.
*/
- preempt_disable();
- c = this_cpu_ptr(s->cpu_slab);
+ do {
+ tid = this_cpu_read(s->cpu_slab->tid);
+ c = raw_cpu_ptr(s->cpu_slab);
+ } while (IS_ENABLED(CONFIG_PREEMPT) && unlikely(tid != c->tid));
- tid = c->tid;
- preempt_enable();
+ /* Same with comment on barrier() in slab_alloc_node() */
+ barrier();
if (likely(page == c->page)) {
set_freepointer(s, object, c->freelist);