md: use TASK_IDLE instead of blocking signals

Hi - I submit this patch for the next merge window:

Some times ago, I made a patch f9c79bc0 that blocks signals around the
schedule() calls in MD. The MD subsystem needs to do an uninterruptible
sleep that is not accounted in load average - so we block signals and use
interruptible sleep.

The kernel has a special TASK_IDLE state for this purpose, so we can use
it instead of blocking signals. This patch doesn't fix any bug, it just
makes the code simpler.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Acked-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

drivers/md/raid1.c

@@ -37,7 +37,6 @@
 #include <linux/module.h>
 #include <linux/seq_file.h>
 #include <linux/ratelimit.h>
-#include <linux/sched/signal.h>
 
 #include <trace/events/block.h>
 
@@ -1320,18 +1319,14 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
 		 */
 		DEFINE_WAIT(w);
 		for (;;) {
-			sigset_t full, old;
 			prepare_to_wait(&conf->wait_barrier,
-					&w, TASK_INTERRUPTIBLE);
+					&w, TASK_IDLE);
 			if (!mddev_is_clustered(mddev) ||
 			    !md_cluster_ops->area_resyncing(mddev, WRITE,
 							bio->bi_iter.bi_sector,
 							bio_end_sector(bio)))
 				break;
-			sigfillset(&full);
-			sigprocmask(SIG_BLOCK, &full, &old);
 			schedule();
-			sigprocmask(SIG_SETMASK, &old, NULL);
 		}
 		finish_wait(&conf->wait_barrier, &w);
 	}

drivers/md/raid5.c

@@ -55,7 +55,6 @@
 #include <linux/ratelimit.h>
 #include <linux/nodemask.h>
 #include <linux/flex_array.h>
-#include <linux/sched/signal.h>
 
 #include <trace/events/block.h>
 #include <linux/list_sort.h>