md: remove flag RemoveSynchronized

rcu is not used correctly here, because synchronize_rcu() is called
before replacing old value, for example:

remove_and_add_spares   // other path
 synchronize_rcu
 // called before replacing old value
 set_bit(RemoveSynchronized)
                        rcu_read_lock()
                        rdev = conf->mirros[].rdev
 pers->hot_remove_disk
  conf->mirros[].rdev = NULL;
  if (!test_bit(RemoveSynchronized))
   synchronize_rcu
   /*
    * won't be called, and won't wait
    * for concurrent readers to be done.
    */
                        // access rdev after remove_and_add_spares()
                        rcu_read_unlock()

Fortunately, there is a separate rcu protection to prevent such rdev
to be freed:

md_kick_rdev_from_array		//other path
				rcu_read_lock()
				rdev = conf->mirros[].rdev
list_del_rcu(&rdev->same_set)

				rcu_read_unlock()
				/*
				 * rdev can be removed from conf, but
				 * rdev won't be freed.
				 */
synchronize_rcu()
free rdev

Hence remove this useless flag and prepare to remove rcu protection to
access rdev from 'conf'.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20231125081604.3939938-2-yukuai1@huaweicloud.com

1 files changed, 0 insertions, 5 deletions

diff --git a/drivers/md/md.h b/drivers/md/md.h
index ade83af123a2..8d881cc59799 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -190,11 +190,6 @@ enum flag_bits {
 				 * than other devices in the array
 				 */
 	ClusterRemove,
-	RemoveSynchronized,	/* synchronize_rcu() was called after
-				 * this device was known to be faulty,
-				 * so it is safe to remove without
-				 * another synchronize_rcu() call.
-				 */
 	ExternalBbl,            /* External metadata provides bad
 				 * block management for a disk
 				 */