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From cab114c5ca870e5f1b57fb2602cd9a038271c2e0 Mon Sep 17 00:00:00 2001
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From: Corey Hickey <bugfood-c@fatooh.org>
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Date: Mon, 11 Feb 2019 17:18:38 -0800
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Subject: [RHEL7.7 PATCH 16/21] Fix reshape for decreasing data offset
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...when not changing the number of disks.
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This patch needs context to explain. These are the relevant parts of
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the original code (condensed and annotated):
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if (dir > 0) {
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/* Increase data offset (reshape backwards) */
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if (data_offset < sd->data_offset + min) {
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pr_err("--data-offset too small on %s\n",
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dn);
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goto release;
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}
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} else {
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/* Decrease data offset (reshape forwards) */
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if (data_offset < sd->data_offset - min) {
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pr_err("--data-offset too small on %s\n",
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dn);
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goto release;
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}
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}
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When this code is reached, mdadm has already decided on a reshape
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direction. When increasing the data offset, the reshape runs backwards
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(dir==1); when decreasing the data offset, the reshape runs forwards
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(dir==-1).
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The conditional within the backwards reshape is correct: the requested
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offset must be larger than the old offset plus a minimum delta; thus the
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reshape has room to work.
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For the forwards reshape, the requested offset needs to be smaller than
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the old offset minus a minimum delta; to do this correctly, the
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comparison must be reversed.
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Also update the error message.
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Note: I have tested this change on a RAID 5 on Linux 4.18.0 and verified
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that there were no errors from the kernel and that the device data
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remained intact. I do not know if there are considerations for different
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RAID levels.
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Signed-off-by: Corey Hickey <bugfood-c@fatooh.org>
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Signed-off-by: Jes Sorensen <jsorensen@fb.com>
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---
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Grow.c | 4 ++--
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1 file changed, 2 insertions(+), 2 deletions(-)
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diff --git a/Grow.c b/Grow.c
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index 6d32661..764374f 100644
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--- a/Grow.c
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+++ b/Grow.c
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@@ -2613,8 +2613,8 @@ static int set_new_data_offset(struct mdinfo *sra, struct supertype *st,
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goto release;
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}
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if (data_offset != INVALID_SECTORS &&
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- data_offset < sd->data_offset - min) {
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- pr_err("--data-offset too small on %s\n",
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+ data_offset > sd->data_offset - min) {
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+ pr_err("--data-offset too large on %s\n",
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dn);
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goto release;
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}
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--
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2.7.5
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