diff options
Diffstat (limited to 'kernel/futex.c')
| -rw-r--r-- | kernel/futex.c | 50 |
1 files changed, 41 insertions, 9 deletions
diff --git a/kernel/futex.c b/kernel/futex.c index 221f2128a43..06968cd7920 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -60,6 +60,8 @@ #include "rtmutex_common.h" +int __read_mostly futex_cmpxchg_enabled; + #define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8) /* @@ -469,6 +471,8 @@ void exit_pi_state_list(struct task_struct *curr) struct futex_hash_bucket *hb; union futex_key key; + if (!futex_cmpxchg_enabled) + return; /* * We are a ZOMBIE and nobody can enqueue itself on * pi_state_list anymore, but we have to be careful @@ -1870,6 +1874,8 @@ asmlinkage long sys_set_robust_list(struct robust_list_head __user *head, size_t len) { + if (!futex_cmpxchg_enabled) + return -ENOSYS; /* * The kernel knows only one size for now: */ @@ -1894,6 +1900,9 @@ sys_get_robust_list(int pid, struct robust_list_head __user * __user *head_ptr, struct robust_list_head __user *head; unsigned long ret; + if (!futex_cmpxchg_enabled) + return -ENOSYS; + if (!pid) head = current->robust_list; else { @@ -1997,6 +2006,9 @@ void exit_robust_list(struct task_struct *curr) unsigned long futex_offset; int rc; + if (!futex_cmpxchg_enabled) + return; + /* * Fetch the list head (which was registered earlier, via * sys_set_robust_list()): @@ -2051,7 +2063,7 @@ void exit_robust_list(struct task_struct *curr) long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout, u32 __user *uaddr2, u32 val2, u32 val3) { - int ret; + int ret = -ENOSYS; int cmd = op & FUTEX_CMD_MASK; struct rw_semaphore *fshared = NULL; @@ -2083,13 +2095,16 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout, ret = futex_wake_op(uaddr, fshared, uaddr2, val, val2, val3); break; case FUTEX_LOCK_PI: - ret = futex_lock_pi(uaddr, fshared, val, timeout, 0); + if (futex_cmpxchg_enabled) + ret = futex_lock_pi(uaddr, fshared, val, timeout, 0); break; case FUTEX_UNLOCK_PI: - ret = futex_unlock_pi(uaddr, fshared); + if (futex_cmpxchg_enabled) + ret = futex_unlock_pi(uaddr, fshared); break; case FUTEX_TRYLOCK_PI: - ret = futex_lock_pi(uaddr, fshared, 0, timeout, 1); + if (futex_cmpxchg_enabled) + ret = futex_lock_pi(uaddr, fshared, 0, timeout, 1); break; default: ret = -ENOSYS; @@ -2145,8 +2160,29 @@ static struct file_system_type futex_fs_type = { static int __init init(void) { - int i = register_filesystem(&futex_fs_type); + u32 curval; + int i; + + /* + * This will fail and we want it. Some arch implementations do + * runtime detection of the futex_atomic_cmpxchg_inatomic() + * functionality. We want to know that before we call in any + * of the complex code paths. Also we want to prevent + * registration of robust lists in that case. NULL is + * guaranteed to fault and we get -EFAULT on functional + * implementation, the non functional ones will return + * -ENOSYS. + */ + curval = cmpxchg_futex_value_locked(NULL, 0, 0); + if (curval == -EFAULT) + futex_cmpxchg_enabled = 1; + for (i = 0; i < ARRAY_SIZE(futex_queues); i++) { + plist_head_init(&futex_queues[i].chain, &futex_queues[i].lock); + spin_lock_init(&futex_queues[i].lock); + } + + i = register_filesystem(&futex_fs_type); if (i) return i; @@ -2156,10 +2192,6 @@ static int __init init(void) return PTR_ERR(futex_mnt); } - for (i = 0; i < ARRAY_SIZE(futex_queues); i++) { - plist_head_init(&futex_queues[i].chain, &futex_queues[i].lock); - spin_lock_init(&futex_queues[i].lock); - } return 0; } __initcall(init); |