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-rw-r--r--drivers/md/raid1.h12
1 files changed, 12 insertions, 0 deletions
diff --git a/drivers/md/raid1.h b/drivers/md/raid1.h
index c7294e7557e0..eb84bc68e2fd 100644
--- a/drivers/md/raid1.h
+++ b/drivers/md/raid1.h
@@ -26,6 +26,18 @@
#define BARRIER_BUCKETS_NR_BITS (PAGE_SHIFT - ilog2(sizeof(atomic_t)))
#define BARRIER_BUCKETS_NR (1<<BARRIER_BUCKETS_NR_BITS)
+/* Note: raid1_info.rdev can be set to NULL asynchronously by raid1_remove_disk.
+ * There are three safe ways to access raid1_info.rdev.
+ * 1/ when holding mddev->reconfig_mutex
+ * 2/ when resync/recovery is known to be happening - i.e. in code that is
+ * called as part of performing resync/recovery.
+ * 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 raid1_info {
struct md_rdev *rdev;
sector_t head_position;