mds/quiesce: agent: avoid a race condition with rapid db updates#56956
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leonid-s-usov merged 1 commit intomainfrom Apr 18, 2024
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mds/quiesce: agent: avoid a race condition with rapid db updates#56956leonid-s-usov merged 1 commit intomainfrom
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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/65545 Signed-off-by: Leonid Usov <leonid.usov@ibm.com>
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batrick
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Apr 17, 2024
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Passed 8 tests on ubuntu machines here: https://pulpito.ceph.com/leonidus-2024-04-18_07:15:14-fs-wip-lusov-quiesce-agent-race-distro-default-smithi/ the other tests were dead due to an infra issue |
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jenkins test api |
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The downstream backport: https://gitlab.cee.redhat.com/ceph/ceph/-/merge_requests/597 |
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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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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: ceph#56956 Signed-off-by: Leonid Usov <leonid.usov@ibm.com> (cherry picked from commit 2a3faf1)
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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 additems 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 into
pending, while the same new rootcould have already been seen and posted into the
workingset.This would lead to submitting the same new root twice.
Without the
workingset such race isn't possible.Fixes: https://tracker.ceph.com/issues/65545
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