From bc2eecd7ecce40af43b6eb3d256b6076257df846 Mon Sep 17 00:00:00 2001 From: Nicolas Pitre Date: Tue, 1 Aug 2017 00:31:32 -0400 Subject: [PATCH] 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: Nicolas Pitre Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: Darren Hart Link: http://lkml.kernel.org/r/alpine.LFD.2.20.1708010024190.5981@knanqh.ubzr --- include/linux/futex.h | 7 ++++++- init/Kconfig | 7 ++++++- kernel/futex.c | 22 ++++++++++++++++++++++ kernel/locking/rtmutex_common.h | 29 +++++++++++++++++++++++++++++ 4 files changed, 63 insertions(+), 2 deletions(-) diff --git a/include/linux/futex.h b/include/linux/futex.h index 7c5b694864cd..f36bfd26f998 100644 --- a/include/linux/futex.h +++ b/include/linux/futex.h @@ -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 diff --git a/init/Kconfig b/init/Kconfig index 8514b25db21c..5f0ef850e808 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -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 diff --git a/kernel/futex.c b/kernel/futex.c index 16dbe4c93895..ad0af4df1b9d 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -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; diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h index 72ad45a9a794..8d039b928d61 100644 --- a/kernel/locking/rtmutex_common.h +++ b/kernel/locking/rtmutex_common.h @@ -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: */ -- GitLab