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From: yizhi.fzh <[email protected]>
Subject: [PATCH v2 2/2] Disallow [LW]LockAcquire when holding a spin lock-file-mode
Date: Thu, 4 Jan 2024 22:19:50 +0800

Spinlocks are intended for *very* short-term locks, but sometimes it is
misused, this commit guards no [LW]LockAcquire should be called when
holding a spin lock.
---
 src/backend/storage/buffer/bufmgr.c |  1 +
 src/backend/storage/lmgr/lock.c     |  2 ++
 src/backend/storage/lmgr/lwlock.c   |  2 ++
 src/backend/utils/init/globals.c    |  1 +
 src/include/storage/buf_internals.h |  1 +
 src/include/storage/spin.h          | 24 ++++++++++++++++++++++--
 6 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 9f9d3f24ac..d2534ee9aa 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -5419,6 +5419,7 @@ LockBufHdr(BufferDesc *desc)
 		perform_spin_delay(&delayStatus);
 	}
 	finish_spin_delay(&delayStatus);
+	START_SPIN_LOCK();
 	return old_buf_state | BM_LOCKED;
 }
 
diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c
index b8c57b3e16..0710adbef8 100644
--- a/src/backend/storage/lmgr/lock.c
+++ b/src/backend/storage/lmgr/lock.c
@@ -776,6 +776,8 @@ LockAcquireExtended(const LOCKTAG *locktag,
 	bool		found_conflict;
 	bool		log_lock = false;
 
+	Assert(SpinLockCount == 0);
+
 	if (lockmethodid <= 0 || lockmethodid >= lengthof(LockMethods))
 		elog(ERROR, "unrecognized lock method: %d", lockmethodid);
 	lockMethodTable = LockMethods[lockmethodid];
diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c
index 315a78cda9..5709cadcd5 100644
--- a/src/backend/storage/lmgr/lwlock.c
+++ b/src/backend/storage/lmgr/lwlock.c
@@ -1205,6 +1205,8 @@ LWLockAcquire(LWLock *lock, LWLockMode mode)
 
 	Assert(mode == LW_SHARED || mode == LW_EXCLUSIVE);
 
+	Assert(SpinLockCount == 0);
+
 	PRINT_LWDEBUG("LWLockAcquire", lock, mode);
 
 #ifdef LWLOCK_STATS
diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c
index 60bc1217fb..125dc53375 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -40,6 +40,7 @@ volatile sig_atomic_t IdleStatsUpdateTimeoutPending = false;
 volatile uint32 InterruptHoldoffCount = 0;
 volatile uint32 QueryCancelHoldoffCount = 0;
 volatile uint32 CritSectionCount = 0;
+volatile uint32 SpinLockCount = 0;
 
 int			MyProcPid;
 pg_time_t	MyStartTime;
diff --git a/src/include/storage/buf_internals.h b/src/include/storage/buf_internals.h
index 2c4fd92e39..be2d090308 100644
--- a/src/include/storage/buf_internals.h
+++ b/src/include/storage/buf_internals.h
@@ -363,6 +363,7 @@ UnlockBufHdr(BufferDesc *desc, uint32 buf_state)
 {
 	pg_write_barrier();
 	pg_atomic_write_u32(&desc->state, buf_state & (~BM_LOCKED));
+	END_SPIN_LOCK();
 }
 
 /* in bufmgr.c */
diff --git a/src/include/storage/spin.h b/src/include/storage/spin.h
index 5d809cc980..c1b96a047f 100644
--- a/src/include/storage/spin.h
+++ b/src/include/storage/spin.h
@@ -56,12 +56,32 @@
 #include "storage/pg_sema.h"
 #endif
 
+extern PGDLLIMPORT volatile uint32 SpinLockCount;
+
+#define START_SPIN_LOCK() (SpinLockCount++)
+#define END_SPIN_LOCK() \
+do { \
+	Assert(SpinLockCount > 0); \
+	SpinLockCount--; \
+} while(0)
 
 #define SpinLockInit(lock)	S_INIT_LOCK(lock)
 
-#define SpinLockAcquire(lock) S_LOCK(lock)
+#define SpinLockAcquire(lock) \
+	do \
+	{ \
+		S_LOCK(lock); \
+		START_SPIN_LOCK(); \
+	} while (false);
+
+
+#define SpinLockRelease(lock) \
+	do \
+	{ \
+		S_UNLOCK(lock); \
+		END_SPIN_LOCK(); \
+	} while (false);
 
-#define SpinLockRelease(lock) S_UNLOCK(lock)
 
 #define SpinLockFree(lock)	S_LOCK_FREE(lock)
 
-- 
2.34.1


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