[backport 3.3] memtx: fix a crash caused by mhash misusage in MVCC#11167
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sergepetrenko merged 1 commit intorelease/3.3from Feb 19, 2025
Merged
[backport 3.3] memtx: fix a crash caused by mhash misusage in MVCC#11167sergepetrenko merged 1 commit intorelease/3.3from
sergepetrenko merged 1 commit intorelease/3.3from
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We use mhash in memtx MVCC to store trackers of reads that have read nothing, we call them point holes. When handling a write to such hole, the tracker should be deleted because we can use the new tuple to store reads instead. Deletion flow in mhash is: we find bucket of the element with `find`, then we free the bucket with `del`. It can seem that the element is not needed on `del` because bucket id is used. However, it can be used on incremental resize of mhash. And, since we delete the point holes before releasing the bucket in mhash, in the rare case of incremental resize Tarantool will be aborted by mhash consistency check. The commit fixes the problem - simply release the bucket before deleting the object. Along the way, the commit fixes another misusage that doesn't actually break something. Method `put_slot` is internal so shouldn't be used manually - let's use more convenient `get` instead. Closes #11022 NO_DOC=bugfix (cherry picked from commit 7c73e24)
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(This PR is a backport of #11162 to
release/3.3to a future3.3.2release.)We use mhash in memtx MVCC to store trackers of reads that have read nothing, we call them point holes. When handling a write to such hole, the tracker should be deleted because we can use the new tuple to store reads instead. Deletion flow in mhash is: we find bucket of the element with
find, then we free the bucket withdel. It can seem that the element is not needed ondelbecause bucket id is used. However, it can be used on incremental resize of mhash. And, since we delete the point holes before releasing the bucket in mhash, in the rare case of incremental resize Tarantool will be aborted by mhash consistency check. The commit fixes the problem - simply release the bucket before deleting the object.Along the way, the commit fixes another misusage that doesn't acutally break something. Method
put_slotis internal so shouldn't be used manually - let's use more convenientgetinstead.Closes #11022