DAOS-18487 placement: fix a bug in shard remapping chain #17535
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For the case of 2nd remap, if the spare target is DOWN2UP need to set fs_down2up flag, to make it be able to set shard's po_rebuilding flag at the end. One example case - Target A is DOWN, rebuild completed and status changed to DOWNOUT Target B is DOWN, rebuild started but not completed but admin do the reint, its status change to UP and with DOWN2UP flag. In object layout calculation, one shard firstly located in Target A, but 1st remap to Target B, but still need to do 2nd remap. In this case should set fs_down2up flag which is not set in the 1st remap, to avoid not be able to set shard's po_rebuilding flag so will cause read from it (invalid place). This bug could cause data corruption (mostly like with cause shard losing). Signed-off-by: Xuezhao Liu <xuezhao.liu@hpe.com>
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wangshilong
approved these changes
Feb 10, 2026
NiuYawei
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Feb 10, 2026
kccain
approved these changes
Feb 10, 2026
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kccain
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this area of the code is a little new to me, but changes seem reasonable after some preliminary study of the code.
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For the case of 2nd remap, if the spare target is DOWN2UP need to set fs_down2up flag, to make it be able to set shard's po_rebuilding flag at the end.
One example case -
Target A is DOWN, rebuild completed and status changed to DOWNOUT
Target B is DOWN, rebuild started but not completed but admin do the reint,
its status change to UP and with DOWN2UP flag.
In object layout calculation, one shard firstly located in Target A, but 1st remap to Target B, but still need to do 2nd remap. In this case should set fs_down2up flag which is not set in the 1st remap, to avoid not be able to set shard's po_rebuilding flag so will cause read from it (invalid place).
This bug could cause data corruption (mostly like with cause shard losing).
Steps for the author:
After all prior steps are complete: