[PATCH v2] md/raid1: Add check for missing source disk in process_checks()

[Meir Elisha <meir.elisha@xxxxxxxxxxx>]

During recovery/check operations, the process_checks function loops
through available disks to find a 'primary' source with successfully
read data.

If no suitable source disk is found after checking all possibilities,
the 'primary' index will reach conf->raid_disks * 2. Add an explicit
check for this condition after the loop. If no source disk was found,
print an error message and return early to prevent further processing
without a valid primary source.

Signed-off-by: Meir Elisha <meir.elisha@xxxxxxxxxxx>
---
Changes from v1:
	- Don't fix read errors on recovery/check

This was observed when forcefully disconnecting all iSCSI devices backing
a RAID1 array(using --failfast flag) during a check operation, causing
all reads within process_checks to fail. The resulting kernel oops shows:

  BUG: kernel NULL pointer dereference, address: 0000000000000040
  RIP: 0010:process_checks+0x25e/0x5e0 [raid1]
  Code: ... <4c> 8b 53 40 ... // mov r10,[rbx+0x40]
  Call Trace:
   process_checks
   sync_request_write
   raid1d
   md_thread
   kthread
   ret_from_fork

 drivers/md/raid1.c | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 0efc03cea24e..de9bccbe7337 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -2200,14 +2200,9 @@ static int fix_sync_read_error(struct r1bio *r1_bio)
 				if (!rdev_set_badblocks(rdev, sect, s, 0))
 					abort = 1;
 			}
-			if (abort) {
-				conf->recovery_disabled =
-					mddev->recovery_disabled;
-				set_bit(MD_RECOVERY_INTR, &mddev->recovery);
-				md_done_sync(mddev, r1_bio->sectors, 0);
-				put_buf(r1_bio);
+			if (abort)
 				return 0;
-			}
+
 			/* Try next page */
 			sectors -= s;
 			sect += s;
@@ -2346,10 +2341,21 @@ static void sync_request_write(struct mddev *mddev, struct r1bio *r1_bio)
 	int disks = conf->raid_disks * 2;
 	struct bio *wbio;
 
-	if (!test_bit(R1BIO_Uptodate, &r1_bio->state))
-		/* ouch - failed to read all of that. */
-		if (!fix_sync_read_error(r1_bio))
+	if (!test_bit(R1BIO_Uptodate, &r1_bio->state)) {
+		/*
+		 * ouch - failed to read all of that.
+		 * No need to fix read error for check/repair
+		 * because all member disks are read.
+		 */
+		if (test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery) ||
+		    !fix_sync_read_error(r1_bio)) {
+			conf->recovery_disabled = mddev->recovery_disabled;
+			set_bit(MD_RECOVERY_INTR, &mddev->recovery);
+			md_done_sync(mddev, r1_bio->sectors, 0);
+			put_buf(r1_bio);
 			return;
+		}
+	}
 
 	if (test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery))
 		process_checks(r1_bio);
-- 
2.34.1