The patch titled
srcu comments
has been added to the -mm tree. Its filename is
srcu-3-rcu-variant-permitting-read-side-blocking-comments.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: srcu comments
From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Add verbiage to an existing comment.
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
kernel/srcu.c | 19 +++++++++++++++++++
1 files changed, 19 insertions(+)
diff -puN kernel/srcu.c~srcu-3-rcu-variant-permitting-read-side-blocking-comments kernel/srcu.c
--- a/kernel/srcu.c~srcu-3-rcu-variant-permitting-read-side-blocking-comments
+++ a/kernel/srcu.c
@@ -211,6 +211,25 @@ void synchronize_srcu(struct srcu_struct
* More importantly, it also forces the corresponding SRCU read-side
* critical sections to have also completed, and the corresponding
* references to SRCU-protected data items to be dropped.
+ *
+ * Note:
+ *
+ * Despite what you might think at first glance, the
+ * preceding synchronize_sched() -must- be within the
+ * critical section ended by the following mutex_unlock().
+ * Otherwise, a task taking the early exit can race
+ * with a srcu_read_unlock(), which might have executed
+ * just before the preceding srcu_readers_active() check,
+ * and whose CPU might have reordered the srcu_read_unlock()
+ * with the preceding critical section. In this case, there
+ * is nothing preventing the synchronize_sched() task that is
+ * taking the early exit from freeing a data structure that
+ * is still being referenced (out of order) by the task
+ * doing the srcu_read_unlock().
+ *
+ * Alternatively, the comparison with "2" on the early exit
+ * could be changed to "3", but this increases synchronize_srcu()
+ * latency for bulk loads. So the current code is preferred.
*/
mutex_unlock(&sp->mutex);
_
Patches currently in -mm which might be from paulmck@xxxxxxxxxx are
radix-tree-rcu-lockless-readside.patch
adix-tree-rcu-lockless-readside-update.patch
rcu-add-lock-annotations-to-rcu_bh_torture_read_lockunlock.patch
memory-ordering-in-__kfifo-primitives.patch
srcu-3-rcu-variant-permitting-read-side-blocking.patch
srcu-3-rcu-variant-permitting-read-side-blocking-fix.patch
srcu-3-rcu-variant-permitting-read-side-blocking-srcu-add-lock-annotations.patch
srcu-3-rcu-variant-permitting-read-side-blocking-comments.patch
srcu-3-add-srcu-operations-to-rcutorture.patch
srcu-3-add-srcu-operations-to-rcutorture-fix.patch
add-srcu-based-notifier-chains.patch
add-srcu-based-notifier-chains-cleanup.patch
srcu-report-out-of-memory-errors.patch
srcu-report-out-of-memory-errors-fixlet.patch
cpufreq-make-the-transition_notifier-chain-use-srcu.patch
rcu-add-module_author-to-rcutorture-module.patch
rcu-fix-incorrect-description-of-default-for-rcutorture.patch
rcu-mention-rcu_bh-in-description-of-rcutortures.patch
rcu-avoid-kthread_stop-on-invalid-pointer-if-rcutorture.patch
rcu-fix-sign-bug-making-rcu_random-always-return-the-same.patch
rcu-add-fake-writers-to-rcutorture.patch
rcu-add-fake-writers-to-rcutorture-tidy.patch
-
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
