Question about raid1_make_request

From: Robert LeBlanc <robert@leblancnet.us>
To: linux-raid@vger.kernel.org
Subject: Question about raid1_make_request
Date: Mon, 28 Nov 2016 16:41:22 -0700	[thread overview]
Message-ID: <CAANLjFpb0ZCEVtvaib8nsoKhKZs55agy35HEByeo1g1OSWBGjg@mail.gmail.com> (raw)

I'm looking through the code and am wondering why this is at the start
of raid1_make_request. It seems that it is only needed for WRITE and
would unnecessarily delay READ requests waiting for the superblock.
Would it make more sense to put this at the start of the WRITE branch?
What am I missing?

1057         /*
1058          * Register the new request and wait if the
reconstruction
1059          * thread has put up a bar for new requests.
1060          * Continue immediately if no resync is active currently.
1061          */
1062
1063         md_write_start(mddev, bio); /* wait on superblock update
early */
1064
1065         if (bio_data_dir(bio) == WRITE &&
1066             ((bio_end_sector(bio) > mddev->suspend_lo &&
1067             bio->bi_iter.bi_sector < mddev->suspend_hi) ||
1068             (mddev_is_clustered(mddev) &&
1069              md_cluster_ops->area_resyncing(mddev, WRITE,
1070                      bio->bi_iter.bi_sector,
bio_end_sector(bio))))) {
1071                 /* As the suspend_* range is controlled by
1072                  * userspace, we want an interruptible
1073                  * wait.
1074                  */
1075                 DEFINE_WAIT(w);
1076                 for (;;) {
1077                         flush_signals(current);
1078                         prepare_to_wait(&conf->wait_barrier,
1079                                         &w, TASK_INTERRUPTIBLE);
1080                         if (bio_end_sector(bio) <=
mddev->suspend_lo ||
1081                             bio->bi_iter.bi_sector >=
mddev->suspend_hi ||
1082                             (mddev_is_clustered(mddev) &&
1083
!md_cluster_ops->area_resyncing(mddev, WRITE,
1084                                      bio->bi_iter.bi_sector,
bio_end_sector(bio))))
1085                                 break;
1086                         schedule();
1087                 }
1088                 finish_wait(&conf->wait_barrier, &w);
1089         }
1090
1091         start_next_window = wait_barrier(conf, bio);
1092
1093         bitmap = mddev->bitmap;
1094

Thanks

----------------
Robert LeBlanc
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