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Check target slot state in prefetch_wait_for (#11779)

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## Problem

See https://neondb.slack.com/archives/C04DGM6SMTM/p1745599814030679

Assume the following scenario: prefetch_wait_for is doing
`CHECK_FOR_INTERRUPTS` which tries to load prefetch responses.
In case of error is calls pageserver_disconnect which aborts all
in-flight requests. But such failure is not detected by
`prefetch_wait_for` which returns true. As a result
`communicator_read_at_lsnv` assumes that slot is received, but as far as
asserts are disables at prod, it is not actually checked.
Then it tries to interpret response and ... *SIGSEGV*

## Summary of changes

Check target slot state  in `prefetch_wait_for`.

Resolves https://github.com/neondatabase/cloud/issues/28258

Co-authored-by: Konstantin Knizhnik <knizhnik@neon.tech>
This commit is contained in:
Konstantin Knizhnik
2025-04-30 15:44:59 +03:00
committed by GitHub
parent 60f63c076f
commit 1d68577fbd
1 changed files with 8 additions and 2 deletions
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10
pgxn/neon/communicator.c
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@@ -687,8 +687,14 @@ prefetch_wait_for(uint64 ring_index)
END_PREFETCH_RECEIVE_WORK();
CHECK_FOR_INTERRUPTS();
}
return result;
if (result)
{
/* Check that slot is actually received (srver can be disconnected in prefetch_pump_state called from CHECK_FOR_INTERRUPTS */
PrefetchRequest *slot = GetPrfSlot(ring_index);
return slot->status == PRFS_RECEIVED;
}
return false;
;
}
/*