From 2afa37048fe659bb1f1b3c8aec89824b2f00a892 Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Fri, 18 Sep 2020 00:04:56 +1200 Subject: [PATCH v2 1/3] Allow WaitLatch() to be used without a latch. Due to flaws in commit 3347c982bab, using WaitLatch() without WL_SET_LATCH 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. Discussion: https://postgr.es/m/CA%2BhUKGK1607VmtrDUHQXrsooU%3Dap4g4R2yaoByWOOA3m8xevUQ%40mail.gmail.com --- src/backend/storage/ipc/latch.c | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-) diff --git a/src/backend/storage/ipc/latch.c b/src/backend/storage/ipc/latch.c index 4153cc8557..63c6c97536 100644 --- a/src/backend/storage/ipc/latch.c +++ b/src/backend/storage/ipc/latch.c @@ -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; -- 2.20.1