super1.c: avoid useless sync when bitmap switches from clustered to none
With kernel commit 480523feae58 ("md: only call set_in_sync() when it is expected to succeed."), mddev->in_sync in clustered array is always zero. It makes metadata resync_offset to always zero. When assembling a clusterd array with "-U no-bitmap" option, kernel md layer "mddev->resync_offset == 0" and "mddev->bitmap == NULL" will trigger raid1 do sync on every bitmap chunk. the sync action is useless, we should avoid it. Related kernel flow: ``` md_do_sync mddev->pers->sync_request raid1_sync_request md_bitmap_start_sync(mddev->bitmap, sector_nr, &sync_blocks, 1) __bitmap_start_sync(bitmap, offset,&blocks1, degraded) if (bitmap == NULL) {/* FIXME or bitmap set as 'failed' */ *blocks = 1024; return 1; /* always resync if no bitmap */ } ``` Reprodusible steps: ``` node1 # mdadm -C /dev/md0 -b clustered -e 1.2 -n 2 -l mirror /dev/sd{a,b} node1 # mdadm -Ss (in another shell, executing & watching: watch -n 1 'cat /proc/mdstat') node1 # mdadm -A -U no-bitmap /dev/md0 /dev/sd{a,b} ``` Signed-off-by: Zhao Heming <heming.zhao@suse.com> Signed-off-by: Jes Sorensen <jsorensen@fb.com>
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super1.c
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super1.c
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@ -1346,6 +1346,8 @@ static int update_super1(struct supertype *st, struct mdinfo *info,
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memcpy(bms->uuid, sb->set_uuid, 16);
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} else if (strcmp(update, "no-bitmap") == 0) {
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sb->feature_map &= ~__cpu_to_le32(MD_FEATURE_BITMAP_OFFSET);
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if (bms->version == BITMAP_MAJOR_CLUSTERED && !IsBitmapDirty(devname))
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sb->resync_offset = MaxSector;
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} else if (strcmp(update, "bbl") == 0) {
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/* only possible if there is room after the bitmap, or if
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* there is no bitmap
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