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-rw-r--r--drivers/md/raid5.h12
1 files changed, 12 insertions, 0 deletions
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 2e6123825095..3f8da26032ac 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -450,6 +450,18 @@ enum {
* HANDLE gets cleared if stripe_handle leaves nothing locked.
*/
+/* Note: disk_info.rdev can be set to NULL asynchronously by raid5_remove_disk.
+ * There are three safe ways to access disk_info.rdev.
+ * 1/ when holding mddev->reconfig_mutex
+ * 2/ when resync/recovery/reshape is known to be happening - i.e. in code that
+ * is called as part of performing resync/recovery/reshape.
+ * 3/ while holding rcu_read_lock(), use rcu_dereference to get the pointer
+ * and if it is non-NULL, increment rdev->nr_pending before dropping the RCU
+ * lock.
+ * When .rdev is set to NULL, the nr_pending count checked again and if
+ * it has been incremented, the pointer is put back in .rdev.
+ */
+
struct disk_info {
struct md_rdev *rdev, *replacement;
struct page *extra_page; /* extra page to use in prexor */