From: Tomáš Hodek Date: Mon, 23 Feb 2015 00:00:38 +0000 (+1100) Subject: md/raid1: fix read balance when a drive is write-mostly. X-Git-Tag: v3.19.1~24 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=63a7d0a9160421a23baac407847e484e8488d12a;p=thirdparty%2Fkernel%2Fstable.git md/raid1: fix read balance when a drive is write-mostly. commit d1901ef099c38afd11add4cfb3312c02ef21ec4a upstream. When a drive is marked write-mostly it should only be the target of reads if there is no other option. This behaviour was broken by commit 9dedf60313fa4dddfd5b9b226a0ef12a512bf9dc md/raid1: read balance chooses idlest disk for SSD which causes a write-mostly device to be *preferred* is some cases. Restore correct behaviour by checking and setting best_dist_disk and best_pending_disk rather than best_disk. We only need to test one of these as they are both changed from -1 or >=0 at the same time. As we leave min_pending and best_dist unchanged, any non-write-mostly device will appear better than the write-mostly device. Reported-by: Tomáš Hodek Reported-by: Dark Penguin Signed-off-by: NeilBrown Link: http://marc.info/?l=linux-raid&m=135982797322422 Fixes: 9dedf60313fa4dddfd5b9b226a0ef12a512bf9dc Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c index 40b35be34f8d8..2f2f38f4d83c8 100644 --- a/drivers/md/raid1.c +++ b/drivers/md/raid1.c @@ -560,7 +560,7 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect if (test_bit(WriteMostly, &rdev->flags)) { /* Don't balance among write-mostly, just * use the first as a last resort */ - if (best_disk < 0) { + if (best_dist_disk < 0) { if (is_badblock(rdev, this_sector, sectors, &first_bad, &bad_sectors)) { if (first_bad < this_sector) @@ -569,7 +569,8 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect best_good_sectors = first_bad - this_sector; } else best_good_sectors = sectors; - best_disk = disk; + best_dist_disk = disk; + best_pending_disk = disk; } continue; }