Commit f38b1f24 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'locking-futex-2025-07-29' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 

Pull futex updates from Thomas Gleixner:

 - Switch the reference counting to a RCU based per-CPU reference to
   address a performance bottleneck vs the single instance rcuref
   variant

 - Make the futex selftest build on 32-bit architectures which only
   support 64-bit time_t, e.g. RISCV-32

 - Cleanups and improvements in selftests and futex bench

* tag 'locking-futex-2025-07-29' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  selftests/futex: Fix spelling mistake "Succeffuly" -> "Successfully"
  selftests/futex: Define SYS_futex on 32-bit architectures with 64-bit time_t
  perf bench futex: Remove support for IMMUTABLE
  selftests/futex: Remove support for IMMUTABLE
  futex: Remove support for IMMUTABLE
  futex: Make futex_private_hash_get() static
  futex: Use RCU-based per-CPU reference counting instead of rcuref_t
  selftests/futex: Adapt the private hash test to RCU related changes
parents 02dc9d15 e4089221

include/linux/futex.h

+5 −11
Original line number Diff line number Diff line
@@ -85,18 +85,12 @@ int futex_hash_prctl(unsigned long arg2, unsigned long arg3, unsigned long arg4) 
#ifdef CONFIG_FUTEX_PRIVATE_HASH

int futex_hash_allocate_default(void);

void futex_hash_free(struct mm_struct *mm);



static inline void futex_mm_init(struct mm_struct *mm)

{

	RCU_INIT_POINTER(mm->futex_phash, NULL);

	mm->futex_phash_new = NULL;

	mutex_init(&mm->futex_hash_lock);

}

int futex_mm_init(struct mm_struct *mm);



#else /* !CONFIG_FUTEX_PRIVATE_HASH */

static inline int futex_hash_allocate_default(void) { return 0; }

static inline void futex_hash_free(struct mm_struct *mm) { }

static inline void futex_mm_init(struct mm_struct *mm) { }

static inline int futex_hash_free(struct mm_struct *mm) { return 0; }

static inline int futex_mm_init(struct mm_struct *mm) { return 0; }

#endif /* CONFIG_FUTEX_PRIVATE_HASH */



#else /* !CONFIG_FUTEX */
@@ -118,8 +112,8 @@ static inline int futex_hash_allocate_default(void) 
{

	return 0;

}

static inline void futex_hash_free(struct mm_struct *mm) { }

static inline void futex_mm_init(struct mm_struct *mm) { }

static inline int futex_hash_free(struct mm_struct *mm) { return 0; }

static inline int futex_mm_init(struct mm_struct *mm) { return 0; }



#endif

include/linux/mm_types.h

+5 −0
Original line number Diff line number Diff line
@@ -1070,6 +1070,11 @@ struct mm_struct { 
		struct mutex			futex_hash_lock;

		struct futex_private_hash	__rcu *futex_phash;

		struct futex_private_hash	*futex_phash_new;

		/* futex-ref */

		unsigned long			futex_batches;

		struct rcu_head			futex_rcu;

		atomic_long_t			futex_atomic;

		unsigned int			__percpu *futex_ref;

#endif



		unsigned long hiwater_rss; /* High-watermark of RSS usage */

include/linux/sched/mm.h

+1 −1
Original line number Diff line number Diff line
@@ -140,7 +140,7 @@ static inline bool mmget_not_zero(struct mm_struct *mm) 


/* mmput gets rid of the mappings and all user-space */

extern void mmput(struct mm_struct *);

#ifdef CONFIG_MMU

#if defined(CONFIG_MMU) || defined(CONFIG_FUTEX_PRIVATE_HASH)

/* same as above but performs the slow path from the async context. Can

 * be called from the atomic context as well

 */

include/uapi/linux/prctl.h

+0 −2
Original line number Diff line number Diff line
@@ -367,8 +367,6 @@ struct prctl_mm_map { 
/* FUTEX hash management */

#define PR_FUTEX_HASH			78

# define PR_FUTEX_HASH_SET_SLOTS	1

# define FH_FLAG_IMMUTABLE		(1ULL << 0)

# define PR_FUTEX_HASH_GET_SLOTS	2

# define PR_FUTEX_HASH_GET_IMMUTABLE	3



#endif /* _LINUX_PRCTL_H */

init/Kconfig

+0 −4
Original line number Diff line number Diff line
@@ -1716,13 +1716,9 @@ config FUTEX_PI 
	depends on FUTEX && RT_MUTEXES

	default y



#

# marked broken for performance reasons; gives us one more cycle to sort things out.

#

config FUTEX_PRIVATE_HASH

	bool

	depends on FUTEX && !BASE_SMALL && MMU

	depends on BROKEN

	default y



config FUTEX_MPOL