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Commit bc2eecd7 authored by Nicolas Pitre's avatar Nicolas Pitre Committed by Thomas Gleixner
Browse files

futex: Allow for compiling out PI support 



This makes it possible to preserve basic futex support and compile out the
PI support when RT mutexes are not available.

Signed-off-by: default avatarNicolas Pitre <nico@linaro.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Darren Hart <dvhart@infradead.org>
Link: http://lkml.kernel.org/r/alpine.LFD.2.20.1708010024190.5981@knanqh.ubzr
parent f06e8c58

include/linux/futex.h

+6 −1
Original line number Diff line number Diff line
@@ -54,7 +54,6 @@ union futex_key { 


#ifdef CONFIG_FUTEX

extern void exit_robust_list(struct task_struct *curr);

extern void exit_pi_state_list(struct task_struct *curr);

#ifdef CONFIG_HAVE_FUTEX_CMPXCHG

#define futex_cmpxchg_enabled 1

#else
@@ -64,8 +63,14 @@ extern int futex_cmpxchg_enabled; 
static inline void exit_robust_list(struct task_struct *curr)

{

}

#endif



#ifdef CONFIG_FUTEX_PI

extern void exit_pi_state_list(struct task_struct *curr);

#else

static inline void exit_pi_state_list(struct task_struct *curr)

{

}

#endif



#endif

init/Kconfig

+6 −1
Original line number Diff line number Diff line
@@ -1275,12 +1275,17 @@ config BASE_FULL 
config FUTEX

	bool "Enable futex support" if EXPERT

	default y

	select RT_MUTEXES

	imply RT_MUTEXES

	help

	  Disabling this option will cause the kernel to be built without

	  support for "fast userspace mutexes".  The resulting kernel may not

	  run glibc-based applications correctly.



config FUTEX_PI

	bool

	depends on FUTEX && RT_MUTEXES

	default y



config HAVE_FUTEX_CMPXCHG

	bool

	depends on FUTEX

kernel/futex.c

+22 −0
Original line number Diff line number Diff line
@@ -875,6 +875,8 @@ static struct task_struct *futex_find_get_task(pid_t pid) 
	return p;

}



#ifdef CONFIG_FUTEX_PI



/*

 * This task is holding PI mutexes at exit time => bad.

 * Kernel cleans up PI-state, but userspace is likely hosed.
@@ -932,6 +934,8 @@ void exit_pi_state_list(struct task_struct *curr) 
	raw_spin_unlock_irq(&curr->pi_lock);

}



#endif



/*

 * We need to check the following states:

 *
@@ -1799,6 +1803,15 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags, 
	struct futex_q *this, *next;

	DEFINE_WAKE_Q(wake_q);



	/*

	 * When PI not supported: return -ENOSYS if requeue_pi is true,

	 * consequently the compiler knows requeue_pi is always false past

	 * this point which will optimize away all the conditional code

	 * further down.

	 */

	if (!IS_ENABLED(CONFIG_FUTEX_PI) && requeue_pi)

		return -ENOSYS;



	if (requeue_pi) {

		/*

		 * Requeue PI only works on two distinct uaddrs. This
@@ -2594,6 +2607,9 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, 
	struct futex_q q = futex_q_init;

	int res, ret;



	if (!IS_ENABLED(CONFIG_FUTEX_PI))

		return -ENOSYS;



	if (refill_pi_state_cache())

		return -ENOMEM;
@@ -2773,6 +2789,9 @@ static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags) 
	struct futex_q *top_waiter;

	int ret;



	if (!IS_ENABLED(CONFIG_FUTEX_PI))

		return -ENOSYS;



retry:

	if (get_user(uval, uaddr))

		return -EFAULT;
@@ -2983,6 +3002,9 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, 
	struct futex_q q = futex_q_init;

	int res, ret;



	if (!IS_ENABLED(CONFIG_FUTEX_PI))

		return -ENOSYS;



	if (uaddr == uaddr2)

		return -EINVAL;

kernel/locking/rtmutex_common.h

+29 −0
Original line number Diff line number Diff line
@@ -40,6 +40,9 @@ struct rt_mutex_waiter { 
/*

 * Various helpers to access the waiters-tree:

 */



#ifdef CONFIG_RT_MUTEXES



static inline int rt_mutex_has_waiters(struct rt_mutex *lock)

{

	return !RB_EMPTY_ROOT(&lock->waiters);
@@ -69,6 +72,32 @@ task_top_pi_waiter(struct task_struct *p) 
			pi_tree_entry);

}



#else



static inline int rt_mutex_has_waiters(struct rt_mutex *lock)

{

	return false;

}



static inline struct rt_mutex_waiter *

rt_mutex_top_waiter(struct rt_mutex *lock)

{

	return NULL;

}



static inline int task_has_pi_waiters(struct task_struct *p)

{

	return false;

}



static inline struct rt_mutex_waiter *

task_top_pi_waiter(struct task_struct *p)

{

	return NULL;

}



#endif



/*

 * lock->owner state tracking:

 */