squid: mds/quiesce: agent: avoid a race condition with rapid db updates#56984
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squid: mds/quiesce: agent: avoid a race condition with rapid db updates#56984
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When new roots begin processing but don't yet make it into the currently tracked set, there is a window for the next update with the same roots to treat them as new. We fix it by simplifying the agent model, getting rid of the intermediate `working` set. Since we never remove or add items into the current roots collection, it's safe to update the current set directly from the pending set. The race was due to the fact that `db_update()` relied on the `current` to deduce new roots into `pending`, while the same new root could have already been seen and posted into the `working` set. This would lead to submitting the same new root twice. Without the `working` set such race isn't possible. Fixes: https://tracker.ceph.com/issues/65570 Original-Issue: https://tracker.ceph.com/issues/65545 Original-PR: #56956 Signed-off-by: Leonid Usov <leonid.usov@ibm.com> (cherry picked from commit 2a3faf1)
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This PR is under test in https://tracker.ceph.com/issues/66101. |
batrick
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May 22, 2024
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When new roots begin processing but don't yet make it into the currently tracked set, there is a window for the next update with the same roots to treat them as new.
We fix it by simplifying the agent model, getting rid of the intermediate
workingset. Since we never remove or add items into the current roots collection, it's safe to update the current set directly from the pending set.The race was due to the fact that
db_update()relied on thecurrentto deduce new roots intopending, while the same new root could have already been seen and posted into theworkingset. This would lead to submitting the same new root twice. Without theworkingset such race isn't possible.Fixes: https://tracker.ceph.com/issues/65570
Original-Issue: https://tracker.ceph.com/issues/65545
Original-PR: #56956
Signed-off-by: Leonid Usov leonid.usov@ibm.com
(cherry picked from commit 2a3faf1)
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