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Fix possible leak of semaphore count.

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Commit 4aec49899e5782247e134f94ce1c6ee926f88e1c reorganized the order
of operations here so that we no longer increment the number of "extra
waits" before locking the semaphore, but it did not change the
starting value of extraWaits from 0 to -1 to compensate.  In the worst
case, this could leak a semaphore count, but that seems to be unlikely
in practice.

Discussion: http://postgr.es/m/CAA4eK1JyVqXiMba+-a589Rk0pyHsyKkGxeumVKjU6Y74hdrVLQ@mail.gmail.com

Amit Kapila, per an off-list report by Dilip Kumar.  Reviewed by me.
This commit is contained in:
Robert Haas 2017-01-05 13:12:16 -05:00
parent 5b4f8f4c6d
commit 603299167f
1 changed files with 2 additions and 1 deletions
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3
src/backend/storage/ipc/procarray.c
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@ -491,7 +491,6 @@ ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid)
volatile PROC_HDR *procglobal = ProcGlobal;
uint32 nextidx;
uint32 wakeidx;
int extraWaits = -1;
/* We should definitely have an XID to clear. */
Assert(TransactionIdIsValid(allPgXact[proc->pgprocno].xid));
@ -518,6 +517,8 @@ ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid)
*/
if (nextidx != INVALID_PGPROCNO)
{
int extraWaits = 0;
/* Sleep until the leader clears our XID. */
for (;;)
{