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Fix off-by-one in LimitAdditionalPins()

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Due to the bug LimitAdditionalPins() could return 0, violating
LimitAdditionalPins()'s API ("One additional pin is always allowed"). This
could be hit when setting shared_buffers very low and using a fair amount of
concurrency.

This bug was introduced in 31966b151e.

Author: "Anton A. Melnikov" <aamelnikov@inbox.ru>
Reported-by: "Anton A. Melnikov" <aamelnikov@inbox.ru>
Reported-by: Victoria Shepard
Discussion: https://postgr.es/m/ae46f2fb-5586-3de0-b54b-1bb0f6410ebd@inbox.ru
Backpatch: 16-
This commit is contained in:
Andres Freund 2023-07-24 19:07:52 -07:00
parent d6677b93c7
commit f3bc519288
1 changed files with 1 additions and 1 deletions
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2
src/backend/storage/buffer/bufmgr.c
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@ -1767,7 +1767,7 @@ LimitAdditionalPins(uint32 *additional_pins)
*/
max_proportional_pins -= PrivateRefCountOverflowed + REFCOUNT_ARRAY_ENTRIES;
if (max_proportional_pins < 0)
if (max_proportional_pins <= 0)
max_proportional_pins = 1;
if (*additional_pins > max_proportional_pins)