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Fix crash when reporting CREATE INDEX progress 

A race condition can make us try to dereference a NULL pointer to the
PGPROC struct of a process that's already finished.  That results in
crashes during REINDEX CONCURRENTLY and CREATE INDEX CONCURRENTLY.

This was introduced in ab0dfc961b, so backpatch to pg12.

Reported by: Justin Pryzby
Reviewed-by: Michaël Paquier
Discussion: https://postgr.es/m/20191012004446.GT10470@telsasoft.com
This commit is contained in:
Alvaro Herrera 2019-10-16 14:51:34 +02:00
parent a524f50d0f
commit 0d21f919eb
2 changed files with 8 additions and 8 deletions
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6
src/backend/commands/indexcmds.c
View File

@ -384,12 +384,14 @@ WaitForOlderSnapshots(TransactionId limitXmin, bool progress)
if (VirtualTransactionIdIsValid(old_snapshots[i]))
{
/* If requested, publish who we're going to wait for. */
if (progress)
{
PGPROC *holder = BackendIdGetProc(old_snapshots[i].backendId);
pgstat_progress_update_param(PROGRESS_WAITFOR_CURRENT_PID,
holder->pid);
if (holder)
pgstat_progress_update_param(PROGRESS_WAITFOR_CURRENT_PID,
holder->pid);
}
VirtualXactLock(old_snapshots[i], true);
}

10
src/backend/storage/lmgr/lmgr.c
View File

@ -900,16 +900,14 @@ WaitForLockersMultiple(List *locktags, LOCKMODE lockmode, bool progress)
while (VirtualTransactionIdIsValid(*lockholders))
{
/*
* If requested, publish who we're going to wait for. This is not
* 100% accurate if they're already gone, but we don't care.
*/
/* If requested, publish who we're going to wait for. */
if (progress)
{
PGPROC *holder = BackendIdGetProc(lockholders->backendId);
pgstat_progress_update_param(PROGRESS_WAITFOR_CURRENT_PID,
holder->pid);
if (holder)
pgstat_progress_update_param(PROGRESS_WAITFOR_CURRENT_PID,
holder->pid);
}
VirtualXactLock(*lockholders, true);
lockholders++;