clean_dead_slots_from_accounts_index unrefs correctly (backport #27461) (backport #27467)

[mergify[bot]]

This is an automatic backport of pull request #27467 done by Mergify. Cherry-pick of 7650bd2ad6feb0f7acca16b9a0da9a7bd9cf87f9 has failed:

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	both modified:   runtime/src/accounts_db.rs

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[jeffwashington]

preparing backport to 1.10 just in case.

[solana-grimes]

:scream: New commits were pushed while the automerge label was present.

[steviez]

preparing backport to 1.10 just in case.

@jeffwashington @brooksprumo @apfitzge - Out of curiosity, will/should this be going into v1.10 (and I guess v1.13 now too)? I saw Brooks make a rec to someone to pull this commit in manually and it looks like the v1.11 backport landed a while back

[jeffwashington]

will/should this be going into v1.10 (and I guess v1.13 now too)?

The current answer is "wait". There was another long standing under refcount bug as well that was recently fixed in master. To be careful with potential instability, it is safer to not fix this type of refcounting bug when it has been in a long time and the effects are unpleasant, but known and not fatal.

[michaelh-laine]

effects are unpleasant, but known and not fatal.

this bug is causing validators to unexpectedly segfault/crash and then crash loop due to systuner using insufficient vm.max_map_count, experienced again just today by Cogent Crypto.

In the absence of a fix nodes either crash every 2-4 weeks or need to be regularly restarted to avoid that. Since there is no EOL for 1.13 known yet perhaps a backport can now be reconsidered as a month has passed since the last comment on this PR?

[t-nelson]

@jeffwashington are we comfortable with backporting this change to 1.13?

[jeffwashington]

this one is being tested now off 1.13: #28582 These validators are running it. I'll hopefully add some more validators as they free up. 8XWpJyTb3dFgEa1nVkTKoTY3ivg1CXN5Wr6149dXTpVP FwQpCUn3bmB27bfhmt9Cepeyn6UPBAXCYWCwkYj5qUd9 3Ex1LtnZa5vwyZgAWC7WXy2aXcn1V1P2bpvK9Z4ZWrHj

[jeffwashington]

went in to 1.13 as #28582