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commit    bd2f46c6559ddcafe7bae5015ac45b69bc014067
Author:   Andres Freund <andres@anarazel.de>
Date:     Tue Jul 25 02:07:52 2023 +0000
First released in: 17.0, 16.0

    Fix off-by-one in LimitAdditionalPins()
    
    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 31966b151e6a.
    
    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-


 src/backend/storage/buffer/bufmgr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 3c59bbd04ea..bd203c21913 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -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)


[parent: b1dc946eee3d]