locking/local_lock, mm: replace localtry_ helpers with local_trylock_t type

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]() helpers that only work 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(&lock);                     // preempt disable
local_lock_irqsave(&lock, ...);        // irq save
if (local_trylock_irqsave(&lock, ...)) // compilation error

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

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.

The local_trylock() without _irqsave can be used to avoid the cost of
disabling/enabling interrupts by only disabling preemption, so
local_trylock() in an interrupt attempting to acquire the same lock will
return false.

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

Note that guard(local_lock)(&lock) works only for "local_lock_t lock".

The patch also makes sure that local_lock_release(l) is called before
WRITE_ONCE(l->acquired, 0).  Though IRQs are disabled at this point the
local_trylock() from NMI will succeed and local_lock_acquire(l) will warn.

Link: https://lkml.kernel.org/r/20250403025514.41186-1-alexei.starovoitov@gmail.com
Fixes: 0aaddfb06882 ("locking/local_lock: Introduce localtry_lock_t")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Daniel Borkman <daniel@iogearbox.net>
Cc: Linus Torvalds <torvalds@linuxfoundation.org>
Cc: Martin KaFai Lau <martin.lau@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 8 insertions, 50 deletions

diff --git a/include/linux/local_lock.h b/include/linux/local_lock.h
index 1a0bc35839e3..16a2ee4f8310 100644
--- a/include/linux/local_lock.h
+++ b/include/linux/local_lock.h
@@ -52,44 +52,23 @@
 	__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
- * @lock:	The lock variable
- * @flags:	Storage for interrupt flags
+ * local_lock_init - Runtime initialize a lock instance
  */
-#define localtry_lock_irqsave(lock, flags)				\
-	__localtry_lock_irqsave(lock, flags)
+#define local_trylock_init(lock)	__local_trylock_init(lock)
 
 /**
- * localtry_trylock - Try to acquire a per CPU local lock.
+ * local_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)		__local_trylock(lock)
 
 /**
- * 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 +76,8 @@
  * 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),