md/raid10: fix softlockup in raid10_unplug

hulk inclusion
category: bugfix
bugzilla: 188628, https://gitee.com/openeuler/kernel/issues/I6WKDR
CVE: NA

--------------------------------

There is no limit to the number of io for raid10 plug, whitch may result
in excessive memory usage and potential softlockup when a large number of
io are submitted at once. There is no good way to fix it now, just add
schedule point to prevent softlockup.

Fixes: 57c67df4 ("md/raid10: submit IO from originating thread instead of md thread.")
Signed-off-by: NLi Nan <linan122@huawei.com>
Reviewed-by: NYu Kuai <yukuai3@huawei.com>
Reviewed-by: NHou Tao <houtao1@huawei.com>

drivers/md/raid10.c

@@ -896,6 +896,7 @@ static void flush_pending_writes(struct r10conf *conf)
 			else
 				submit_bio_noacct(bio);
 			bio = next;
+			cond_resched();
 		}
 		blk_finish_plug(&plug);
 	} else
@@ -1089,6 +1090,7 @@ static void raid10_unplug(struct blk_plug_cb *cb, bool from_schedule)
 		else
 			submit_bio_noacct(bio);
 		bio = next;
+		cond_resched();
 	}
 	kfree(plug);
 }