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Allow WaitLatch() to be used without a latch. 

Due to flaws in commit 3347c982ba, using WaitLatch() without
WL_LATCH_SET could cause an assertion failure or crash.  Repair.

While here, also add a check that the latch we're switching to belongs
to this backend, when changing from one latch to another.

Discussion: https://postgr.es/m/CA%2BhUKGK1607VmtrDUHQXrsooU%3Dap4g4R2yaoByWOOA3m8xevUQ%40mail.gmail.com
This commit is contained in:
Thomas Munro 2020-09-23 15:17:30 +12:00
parent 2e3c19462d
commit 733fa9aa51
1 changed files with 19 additions and 4 deletions
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23
src/backend/storage/ipc/latch.c
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@ -924,7 +924,22 @@ ModifyWaitEvent(WaitEventSet *set, int pos, uint32 events, Latch *latch)
if (events == WL_LATCH_SET)
{
if (latch && latch->owner_pid != MyProcPid)
elog(ERROR, "cannot wait on a latch owned by another process");
set->latch = latch;
/*
* On Unix, we don't need to modify the kernel object because the
* underlying pipe is the same for all latches so we can return
* immediately. On Windows, we need to update our array of handles,
* but we leave the old one in place and tolerate spurious wakeups if
* the latch is disabled.
*/
#if defined(WAIT_USE_WIN32)
if (!latch)
return;
#else
return;
#endif
}
#if defined(WAIT_USE_EPOLL)
@ -1386,7 +1401,7 @@ WaitEventSetWaitBlock(WaitEventSet *set, int cur_timeout,
/* There's data in the self-pipe, clear it. */
drainSelfPipe();
if (set->latch->is_set)
if (set->latch && set->latch->is_set)
{
occurred_events->fd = PGINVALID_SOCKET;
occurred_events->events = WL_LATCH_SET;
@ -1536,7 +1551,7 @@ WaitEventSetWaitBlock(WaitEventSet *set, int cur_timeout,
/* There's data in the self-pipe, clear it. */
drainSelfPipe();
if (set->latch->is_set)
if (set->latch && set->latch->is_set)
{
occurred_events->fd = PGINVALID_SOCKET;
occurred_events->events = WL_LATCH_SET;
@ -1645,7 +1660,7 @@ WaitEventSetWaitBlock(WaitEventSet *set, int cur_timeout,
/* There's data in the self-pipe, clear it. */
drainSelfPipe();
if (set->latch->is_set)
if (set->latch && set->latch->is_set)
{
occurred_events->fd = PGINVALID_SOCKET;
occurred_events->events = WL_LATCH_SET;
@ -1812,7 +1827,7 @@ WaitEventSetWaitBlock(WaitEventSet *set, int cur_timeout,
if (!ResetEvent(set->latch->event))
elog(ERROR, "ResetEvent failed: error code %lu", GetLastError());
if (set->latch->is_set)
if (set->latch && set->latch->is_set)
{
occurred_events->fd = PGINVALID_SOCKET;
occurred_events->events = WL_LATCH_SET;