Message-Id: <20250401005134.14433-1-alexei.starovoitov@gmail.com>
Date: Mon, 31 Mar 2025 17:51:34 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: bpf@...r.kernel.org,
	daniel@...earbox.net,
	andrii@...nel.org,
	martin.lau@...nel.org,
	akpm@...ux-foundation.org,
	peterz@...radead.org,
	vbabka@...e.cz,
	bigeasy@...utronix.de,
	rostedt@...dmis.org,
	shakeel.butt@...ux.dev,
	mhocko@...e.com,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] locking/local_lock, mm: Replace localtry_ helpers with local_trylock_t type

From: Alexei Starovoitov <ast@...nel.org>

Partially revert commit 0aaddfb06882 ("locking/local_lock: Introduce localtry_lock_t").
Remove localtry_*() helpers, since localtry_lock() name might
be misinterpreted as "try lock".

Introduce local_trylock_irqsave() helper that only works
with newly introduced local_trylock_t type.
Note that attempt to use local_trylock_irqsave() with local_lock_t
will cause compilation failure.

Usage and behavior in !PREEMPT_RT:

local_lock_t lock;                     // sizeof(lock) == 0
local_lock_irqsave(&lock, ...);        // irq save
if (local_trylock_irqsave(&lock, ...)) // compilation error

local_trylock_t lock;                  // sizeof(lock) == 4
local_lock_irqsave(&lock, ...);        // irq save and acquired = 1
if (local_trylock_irqsave(&lock, ...)) // if (!acquired) irq save

The existing local_lock_*() macros can be used either with
local_lock_t or local_trylock_t.
With local_trylock_t they set acquired = 1 while local_unlock_*() clears it.

In !PREEMPT_RT local_lock_irqsave(local_lock_t *) disables interrupts
to protect critical section, but it doesn't prevent NMI, so the fully
reentrant code cannot use local_lock_irqsave(local_lock_t *) for
exclusive access.

The local_lock_irqsave(local_trylock_t *) helper disables interrupts
and sets acquired=1, so local_trylock_irqsave(local_trylock_t *) from
NMI attempting to acquire the same lock will return false.

In PREEMPT_RT local_lock_irqsave() maps to preemptible spin_lock().
Map local_trylock_irqsave() to preemptible spin_trylock().
When in hard IRQ or NMI return false right away, since
spin_trylock() is not safe due to explicit locking in the underneath
rt_spin_trylock() implementation. Removing this explicit locking and
attempting only "trylock" is undesired due to PI implications.

Note there is no need to use local_inc for acquired variable,
since it's a percpu variable with strict nesting scopes.

Signed-off-by: Alexei Starovoitov <ast@...nel.org>
---
 include/linux/local_lock.h          |  58 +--------
 include/linux/local_lock_internal.h | 193 ++++++++++------------------
 mm/memcontrol.c                     |  39 +++---
 3 files changed, 95 insertions(+), 195 deletions(-)

diff --git a/include/linux/local_lock.h b/include/linux/local_lock.h
index 1a0bc35839e3..9262109cca51 100644
--- a/include/linux/local_lock.h
+++ b/include/linux/local_lock.h
@@ -52,44 +52,19 @@
 	__local_unlock_irqrestore(lock, flags)
 
 /**
- * localtry_lock_init - Runtime initialize a lock instance
- */
-#define localtry_lock_init(lock)		__localtry_lock_init(lock)
-
-/**
- * localtry_lock - Acquire a per CPU local lock
- * @lock:	The lock variable
- */
-#define localtry_lock(lock)		__localtry_lock(lock)
-
-/**
- * localtry_lock_irq - Acquire a per CPU local lock and disable interrupts
- * @lock:	The lock variable
- */
-#define localtry_lock_irq(lock)		__localtry_lock_irq(lock)
-
-/**
- * localtry_lock_irqsave - Acquire a per CPU local lock, save and disable
- *			 interrupts
+ * local_trylock_irqsave - Try to acquire a per CPU local lock
  * @lock:	The lock variable
  * @flags:	Storage for interrupt flags
- */
-#define localtry_lock_irqsave(lock, flags)				\
-	__localtry_lock_irqsave(lock, flags)
-
-/**
- * localtry_trylock - Try to acquire a per CPU local lock.
- * @lock:	The lock variable
  *
  * The function can be used in any context such as NMI or HARDIRQ. Due to
  * locking constrains it will _always_ fail to acquire the lock in NMI or
  * HARDIRQ context on PREEMPT_RT.
  */
-#define localtry_trylock(lock)		__localtry_trylock(lock)
+#define local_trylock(lock, flags)	__local_trylock(lock, flags)
 
 /**
- * localtry_trylock_irqsave - Try to acquire a per CPU local lock, save and disable
- *			      interrupts if acquired
+ * local_trylock_irqsave - Try to acquire a per CPU local lock, save and disable
+ *			   interrupts if acquired
  * @lock:	The lock variable
  * @flags:	Storage for interrupt flags
  *
@@ -97,29 +72,8 @@
  * locking constrains it will _always_ fail to acquire the lock in NMI or
  * HARDIRQ context on PREEMPT_RT.
  */
-#define localtry_trylock_irqsave(lock, flags)				\
-	__localtry_trylock_irqsave(lock, flags)
-
-/**
- * local_unlock - Release a per CPU local lock
- * @lock:	The lock variable
- */
-#define localtry_unlock(lock)		__localtry_unlock(lock)
-
-/**
- * local_unlock_irq - Release a per CPU local lock and enable interrupts
- * @lock:	The lock variable
- */
-#define localtry_unlock_irq(lock)		__localtry_unlock_irq(lock)
-
-/**
- * localtry_unlock_irqrestore - Release a per CPU local lock and restore
- *			      interrupt flags
- * @lock:	The lock variable
- * @flags:      Interrupt flags to restore
- */
-#define localtry_unlock_irqrestore(lock, flags)			\
-	__localtry_unlock_irqrestore(lock, flags)
+#define local_trylock_irqsave(lock, flags)			\
+	__local_trylock_irqsave(lock, flags)
 
 DEFINE_GUARD(local_lock, local_lock_t __percpu*,
 	     local_lock(_T),
diff --git a/include/linux/local_lock_internal.h b/include/linux/local_lock_internal.h
index 67bd13d142fa..cc79854206df 100644
--- a/include/linux/local_lock_internal.h
+++ b/include/linux/local_lock_internal.h
@@ -15,10 +15,18 @@ typedef struct {
 #endif
 } local_lock_t;
 
+/* local_trylock() and local_trylock_irqsave() only work with local_trylock_t */
 typedef struct {
-	local_lock_t	llock;
-	unsigned int	acquired;
-} localtry_lock_t;
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	struct lockdep_map	dep_map;
+	struct task_struct	*owner;
+#endif
+	/*
+	 * Same layout as local_lock_t with 'acquired' field at the end.
+	 * (local_trylock_t *) will be casted to (local_lock_t *).
+	 */
+	int acquired;
+} local_trylock_t;
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 # define LOCAL_LOCK_DEBUG_INIT(lockname)		\
@@ -63,7 +71,6 @@ static inline void local_lock_debug_init(local_lock_t *l) { }
 #endif /* !CONFIG_DEBUG_LOCK_ALLOC */
 
 #define INIT_LOCAL_LOCK(lockname)	{ LOCAL_LOCK_DEBUG_INIT(lockname) }
-#define INIT_LOCALTRY_LOCK(lockname)	{ .llock = { LOCAL_LOCK_DEBUG_INIT(lockname.llock) }}
 
 #define __local_lock_init(lock)					\
 do {								\
@@ -87,39 +94,88 @@ do {								\
 	local_lock_debug_init(lock);				\
 } while (0)
 
+#define __local_lock_acquire(lock)					\
+	do {								\
+		local_trylock_t *tl;					\
+		local_lock_t *l;					\
+									\
+		l = (local_lock_t *)this_cpu_ptr(lock);			\
+		tl = (local_trylock_t *)l;				\
+		_Generic((lock),					\
+			local_trylock_t *: ({				\
+				lockdep_assert(tl->acquired == 0);	\
+				WRITE_ONCE(tl->acquired, 1);		\
+			}),						\
+			default:(void)0);				\
+		local_lock_acquire(l);					\
+	} while (0)
+
 #define __local_lock(lock)					\
 	do {							\
 		preempt_disable();				\
-		local_lock_acquire(this_cpu_ptr(lock));		\
+		__local_lock_acquire(lock);			\
 	} while (0)
 
 #define __local_lock_irq(lock)					\
 	do {							\
 		local_irq_disable();				\
-		local_lock_acquire(this_cpu_ptr(lock));		\
+		__local_lock_acquire(lock);			\
 	} while (0)
 
 #define __local_lock_irqsave(lock, flags)			\
 	do {							\
 		local_irq_save(flags);				\
-		local_lock_acquire(this_cpu_ptr(lock));		\
+		__local_lock_acquire(lock);			\
+	} while (0)
+
+#define __local_trylock_irqsave(lock, flags)			\
+	({							\
+		local_trylock_t *tl;				\
+								\
+		local_irq_save(flags);				\
+		tl = this_cpu_ptr(lock);			\
+		if (READ_ONCE(tl->acquired) == 1) {		\
+			local_irq_restore(flags);		\
+			tl = NULL;				\
+		} else {					\
+			WRITE_ONCE(tl->acquired, 1);		\
+			local_trylock_acquire(			\
+				(local_lock_t *)tl);		\
+		}						\
+		!!tl;						\
+	})
+
+#define __local_lock_release(lock)					\
+	do {								\
+		local_trylock_t *tl;					\
+		local_lock_t *l;					\
+									\
+		l = (local_lock_t *)this_cpu_ptr(lock);			\
+		tl = (local_trylock_t *)l;				\
+		_Generic((lock),					\
+			local_trylock_t *: ({				\
+				lockdep_assert(tl->acquired == 1);	\
+				WRITE_ONCE(tl->acquired, 0);		\
+			}),						\
+			default:(void)0);				\
+		local_lock_release(l);					\
 	} while (0)
 
 #define __local_unlock(lock)					\
 	do {							\
-		local_lock_release(this_cpu_ptr(lock));		\
+		__local_lock_release(lock);			\
 		preempt_enable();				\
 	} while (0)
 
 #define __local_unlock_irq(lock)				\
 	do {							\
-		local_lock_release(this_cpu_ptr(lock));		\
+		__local_lock_release(lock);			\
 		local_irq_enable();				\
 	} while (0)
 
 #define __local_unlock_irqrestore(lock, flags)			\
 	do {							\
-		local_lock_release(this_cpu_ptr(lock));		\
+		__local_lock_release(lock);			\
 		local_irq_restore(flags);			\
 	} while (0)
 
@@ -132,104 +188,6 @@ do {								\
 #define __local_unlock_nested_bh(lock)				\
 	local_lock_release(this_cpu_ptr(lock))
 
-/* localtry_lock_t variants */
-
-#define __localtry_lock_init(lock)				\
-do {								\
-	__local_lock_init(&(lock)->llock);			\
-	WRITE_ONCE((lock)->acquired, 0);			\
-} while (0)
-
-#define __localtry_lock(lock)					\
-	do {							\
-		localtry_lock_t *lt;				\
-		preempt_disable();				\
-		lt = this_cpu_ptr(lock);			\
-		local_lock_acquire(&lt->llock);			\
-		WRITE_ONCE(lt->acquired, 1);			\
-	} while (0)
-
-#define __localtry_lock_irq(lock)				\
-	do {							\
-		localtry_lock_t *lt;				\
-		local_irq_disable();				\
-		lt = this_cpu_ptr(lock);			\
-		local_lock_acquire(&lt->llock);			\
-		WRITE_ONCE(lt->acquired, 1);			\
-	} while (0)
-
-#define __localtry_lock_irqsave(lock, flags)			\
-	do {							\
-		localtry_lock_t *lt;				\
-		local_irq_save(flags);				\
-		lt = this_cpu_ptr(lock);			\
-		local_lock_acquire(&lt->llock);			\
-		WRITE_ONCE(lt->acquired, 1);			\
-	} while (0)
-
-#define __localtry_trylock(lock)				\
-	({							\
-		localtry_lock_t *lt;				\
-		bool _ret;					\
-								\
-		preempt_disable();				\
-		lt = this_cpu_ptr(lock);			\
-		if (!READ_ONCE(lt->acquired)) {			\
-			WRITE_ONCE(lt->acquired, 1);		\
-			local_trylock_acquire(&lt->llock);	\
-			_ret = true;				\
-		} else {					\
-			_ret = false;				\
-			preempt_enable();			\
-		}						\
-		_ret;						\
-	})
-
-#define __localtry_trylock_irqsave(lock, flags)			\
-	({							\
-		localtry_lock_t *lt;				\
-		bool _ret;					\
-								\
-		local_irq_save(flags);				\
-		lt = this_cpu_ptr(lock);			\
-		if (!READ_ONCE(lt->acquired)) {			\
-			WRITE_ONCE(lt->acquired, 1);		\
-			local_trylock_acquire(&lt->llock);	\
-			_ret = true;				\
-		} else {					\
-			_ret = false;				\
-			local_irq_restore(flags);		\
-		}						\
-		_ret;						\
-	})
-
-#define __localtry_unlock(lock)					\
-	do {							\
-		localtry_lock_t *lt;				\
-		lt = this_cpu_ptr(lock);			\
-		WRITE_ONCE(lt->acquired, 0);			\
-		local_lock_release(&lt->llock);			\
-		preempt_enable();				\
-	} while (0)
-
-#define __localtry_unlock_irq(lock)				\
-	do {							\
-		localtry_lock_t *lt;				\
-		lt = this_cpu_ptr(lock);			\
-		WRITE_ONCE(lt->acquired, 0);			\
-		local_lock_release(&lt->llock);			\
-		local_irq_enable();				\
-	} while (0)
-
-#define __localtry_unlock_irqrestore(lock, flags)		\
-	do {							\
-		localtry_lock_t *lt;				\
-		lt = this_cpu_ptr(lock);			\
-		WRITE_ONCE(lt->acquired, 0);			\
-		local_lock_release(&lt->llock);			\
-		local_irq_restore(flags);			\
-	} while (0)
-
 #else /* !CONFIG_PREEMPT_RT */
 
 /*
@@ -237,10 +195,9 @@ do {								\
  * critical section while staying preemptible.
  */
 typedef spinlock_t local_lock_t;
-typedef spinlock_t localtry_lock_t;
+typedef spinlock_t local_trylock_t;
 
 #define INIT_LOCAL_LOCK(lockname) __LOCAL_SPIN_LOCK_UNLOCKED((lockname))
-#define INIT_LOCALTRY_LOCK(lockname) INIT_LOCAL_LOCK(lockname)
 
 #define __local_lock_init(l)					\
 	do {							\
@@ -283,17 +240,7 @@ do {								\
 	spin_unlock(this_cpu_ptr((lock)));			\
 } while (0)
 
-/* localtry_lock_t variants */
-
-#define __localtry_lock_init(lock)			__local_lock_init(lock)
-#define __localtry_lock(lock)				__local_lock(lock)
-#define __localtry_lock_irq(lock)			__local_lock(lock)
-#define __localtry_lock_irqsave(lock, flags)		__local_lock_irqsave(lock, flags)
-#define __localtry_unlock(lock)				__local_unlock(lock)
-#define __localtry_unlock_irq(lock)			__local_unlock(lock)
-#define __localtry_unlock_irqrestore(lock, flags)	__local_unlock_irqrestore(lock, flags)
-
-#define __localtry_trylock(lock)				\
+#define __local_trylock(lock)					\
 	({							\
 		int __locked;					\
 								\
@@ -308,11 +255,11 @@ do {								\
 		__locked;					\
 	})
 
-#define __localtry_trylock_irqsave(lock, flags)			\
+#define __local_trylock_irqsave(lock, flags)			\
 	({							\
 		typecheck(unsigned long, flags);		\
 		flags = 0;					\
-		__localtry_trylock(lock);			\
+		__local_trylock(lock);				\
 	})
 
 #endif /* CONFIG_PREEMPT_RT */
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 83c2df73e4b6..bca86961754e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1739,7 +1739,7 @@ void mem_cgroup_print_oom_group(struct mem_cgroup *memcg)
 }
 
 struct memcg_stock_pcp {
-	localtry_lock_t stock_lock;
+	local_trylock_t stock_lock;
 	struct mem_cgroup *cached; /* this never be root cgroup */
 	unsigned int nr_pages;
 
@@ -1754,7 +1754,7 @@ struct memcg_stock_pcp {
 #define FLUSHING_CACHED_CHARGE	0
 };
 static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock) = {
-	.stock_lock = INIT_LOCALTRY_LOCK(stock_lock),
+	.stock_lock = INIT_LOCAL_LOCK(stock_lock),
 };
 static DEFINE_MUTEX(percpu_charge_mutex);
 
@@ -1785,11 +1785,10 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages,
 	if (nr_pages > MEMCG_CHARGE_BATCH)
 		return ret;
 
-	if (!localtry_trylock_irqsave(&memcg_stock.stock_lock, flags)) {
-		if (!gfpflags_allow_spinning(gfp_mask))
-			return ret;
-		localtry_lock_irqsave(&memcg_stock.stock_lock, flags);
-	}
+	if (gfpflags_allow_spinning(gfp_mask))
+		local_lock_irqsave(&memcg_stock.stock_lock, flags);
+	else if (!local_trylock_irqsave(&memcg_stock.stock_lock, flags))
+		return ret;
 
 	stock = this_cpu_ptr(&memcg_stock);
 	stock_pages = READ_ONCE(stock->nr_pages);
@@ -1798,7 +1797,7 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages,
 		ret = true;
 	}
 
-	localtry_unlock_irqrestore(&memcg_stock.stock_lock, flags);
+	local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
 
 	return ret;
 }
@@ -1837,14 +1836,14 @@ static void drain_local_stock(struct work_struct *dummy)
 	 * drain_stock races is that we always operate on local CPU stock
 	 * here with IRQ disabled
 	 */
-	localtry_lock_irqsave(&memcg_stock.stock_lock, flags);
+	local_lock_irqsave(&memcg_stock.stock_lock, flags);
 
 	stock = this_cpu_ptr(&memcg_stock);
 	old = drain_obj_stock(stock);
 	drain_stock(stock);
 	clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags);
 
-	localtry_unlock_irqrestore(&memcg_stock.stock_lock, flags);
+	local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
 	obj_cgroup_put(old);
 }
 
@@ -1874,7 +1873,7 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
 {
 	unsigned long flags;
 
-	if (!localtry_trylock_irqsave(&memcg_stock.stock_lock, flags)) {
+	if (!local_trylock_irqsave(&memcg_stock.stock_lock, flags)) {
 		/*
 		 * In case of unlikely failure to lock percpu stock_lock
 		 * uncharge memcg directly.
@@ -1887,7 +1886,7 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
 		return;
 	}
 	__refill_stock(memcg, nr_pages);
-	localtry_unlock_irqrestore(&memcg_stock.stock_lock, flags);
+	local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
 }
 
 /*
@@ -1944,9 +1943,9 @@ static int memcg_hotplug_cpu_dead(unsigned int cpu)
 	stock = &per_cpu(memcg_stock, cpu);
 
 	/* drain_obj_stock requires stock_lock */
-	localtry_lock_irqsave(&memcg_stock.stock_lock, flags);
+	local_lock_irqsave(&memcg_stock.stock_lock, flags);
 	old = drain_obj_stock(stock);
-	localtry_unlock_irqrestore(&memcg_stock.stock_lock, flags);
+	local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
 
 	drain_stock(stock);
 	obj_cgroup_put(old);
@@ -2729,7 +2728,7 @@ static void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
 	unsigned long flags;
 	int *bytes;
 
-	localtry_lock_irqsave(&memcg_stock.stock_lock, flags);
+	local_lock_irqsave(&memcg_stock.stock_lock, flags);
 	stock = this_cpu_ptr(&memcg_stock);
 
 	/*
@@ -2782,7 +2781,7 @@ static void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
 	if (nr)
 		__mod_objcg_mlstate(objcg, pgdat, idx, nr);
 
-	localtry_unlock_irqrestore(&memcg_stock.stock_lock, flags);
+	local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
 	obj_cgroup_put(old);
 }
 
@@ -2792,7 +2791,7 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
 	unsigned long flags;
 	bool ret = false;
 
-	localtry_lock_irqsave(&memcg_stock.stock_lock, flags);
+	local_lock_irqsave(&memcg_stock.stock_lock, flags);
 
 	stock = this_cpu_ptr(&memcg_stock);
 	if (objcg == READ_ONCE(stock->cached_objcg) && stock->nr_bytes >= nr_bytes) {
@@ -2800,7 +2799,7 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
 		ret = true;
 	}
 
-	localtry_unlock_irqrestore(&memcg_stock.stock_lock, flags);
+	local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
 
 	return ret;
 }
@@ -2892,7 +2891,7 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
 	unsigned long flags;
 	unsigned int nr_pages = 0;
 
-	localtry_lock_irqsave(&memcg_stock.stock_lock, flags);
+	local_lock_irqsave(&memcg_stock.stock_lock, flags);
 
 	stock = this_cpu_ptr(&memcg_stock);
 	if (READ_ONCE(stock->cached_objcg) != objcg) { /* reset if necessary */
@@ -2910,7 +2909,7 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
 		stock->nr_bytes &= (PAGE_SIZE - 1);
 	}
 
-	localtry_unlock_irqrestore(&memcg_stock.stock_lock, flags);
+	local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
 	obj_cgroup_put(old);
 
 	if (nr_pages)
-- 
2.47.1

Powered by blists - more mailing lists