diff options
| -rw-r--r-- | include/linux/futex.h | 95 | ||||
| -rw-r--r-- | include/linux/sched.h | 3 | ||||
| -rw-r--r-- | include/linux/threads.h | 3 | ||||
| -rw-r--r-- | kernel/exit.c | 3 | ||||
| -rw-r--r-- | kernel/futex.c | 172 | ||||
| -rw-r--r-- | kernel/sys_ni.c | 4 |
6 files changed, 279 insertions, 1 deletions
diff --git a/include/linux/futex.h b/include/linux/futex.h index 10f96c3..20face6 100644 --- a/include/linux/futex.h +++ b/include/linux/futex.h @@ -1,6 +1,8 @@ #ifndef _LINUX_FUTEX_H #define _LINUX_FUTEX_H +#include <linux/sched.h> + /* Second argument to futex syscall */ @@ -11,10 +13,103 @@ #define FUTEX_CMP_REQUEUE 4 #define FUTEX_WAKE_OP 5 +/* + * Support for robust futexes: the kernel cleans up held futexes at + * thread exit time. + */ + +/* + * Per-lock list entry - embedded in user-space locks, somewhere close + * to the futex field. (Note: user-space uses a double-linked list to + * achieve O(1) list add and remove, but the kernel only needs to know + * about the forward link) + * + * NOTE: this structure is part of the syscall ABI, and must not be + * changed. + */ +struct robust_list { + struct robust_list __user *next; +}; + +/* + * Per-thread list head: + * + * NOTE: this structure is part of the syscall ABI, and must only be + * changed if the change is first communicated with the glibc folks. + * (When an incompatible change is done, we'll increase the structure + * size, which glibc will detect) + */ +struct robust_list_head { + /* + * The head of the list. Points back to itself if empty: + */ + struct robust_list list; + + /* + * This relative offset is set by user-space, it gives the kernel + * the relative position of the futex field to examine. This way + * we keep userspace flexible, to freely shape its data-structure, + * without hardcoding any particular offset into the kernel: + */ + long futex_offset; + + /* + * The death of the thread may race with userspace setting + * up a lock's links. So to handle this race, userspace first + * sets this field to the address of the to-be-taken lock, + * then does the lock acquire, and then adds itself to the + * list, and then clears this field. Hence the kernel will + * always have full knowledge of all locks that the thread + * _might_ have taken. We check the owner TID in any case, + * so only truly owned locks will be handled. + */ + struct robust_list __user *list_op_pending; +}; + +/* + * Are there any waiters for this robust futex: + */ +#define FUTEX_WAITERS 0x80000000 + +/* + * The kernel signals via this bit that a thread holding a futex + * has exited without unlocking the futex. The kernel also does + * a FUTEX_WAKE on such futexes, after setting the bit, to wake + * up any possible waiters: + */ +#define FUTEX_OWNER_DIED 0x40000000 + +/* + * Reserved bit: + */ +#define FUTEX_OWNER_PENDING 0x20000000 + +/* + * The rest of the robust-futex field is for the TID: + */ +#define FUTEX_TID_MASK 0x1fffffff + +/* + * A limit of one million locks held per thread (!) ought to be enough + * for some time. This also protects against a deliberately circular + * list. Not worth introducing an rlimit for this: + */ +#define ROBUST_LIST_LIMIT 1048576 + long do_futex(unsigned long uaddr, int op, int val, unsigned long timeout, unsigned long uaddr2, int val2, int val3); +extern int handle_futex_death(unsigned int *uaddr, struct task_struct *curr); + +#ifdef CONFIG_FUTEX +extern void exit_robust_list(struct task_struct *curr); +#else +static inline void exit_robust_list(struct task_struct *curr) +{ +} +#endif + #define FUTEX_OP_SET 0 /* *(int *)UADDR2 = OPARG; */ #define FUTEX_OP_ADD 1 /* *(int *)UADDR2 += OPARG; */ #define FUTEX_OP_OR 2 /* *(int *)UADDR2 |= OPARG; */ diff --git a/include/linux/sched.h b/include/linux/sched.h index 036d14d2..fd4848f 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -35,6 +35,7 @@ #include <linux/topology.h> #include <linux/seccomp.h> #include <linux/rcupdate.h> +#include <linux/futex.h> #include <linux/auxvec.h> /* For AT_VECTOR_SIZE */ @@ -872,6 +873,8 @@ struct task_struct { int cpuset_mems_generation; int cpuset_mem_spread_rotor; #endif + struct robust_list_head __user *robust_list; + atomic_t fs_excl; /* holding fs exclusive resources */ struct rcu_head rcu; }; diff --git a/include/linux/threads.h b/include/linux/threads.h index b59738a..e646bcd 100644 --- a/include/linux/threads.h +++ b/include/linux/threads.h @@ -28,7 +28,8 @@ #define PID_MAX_DEFAULT (CONFIG_BASE_SMALL ? 0x1000 : 0x8000) /* - * A maximum of 4 million PIDs should be enough for a while: + * A maximum of 4 million PIDs should be enough for a while. + * [NOTE: PID/TIDs are limited to 2^29 ~= 500+ million, see futex.h.] */ #define PID_MAX_LIMIT (CONFIG_BASE_SMALL ? PAGE_SIZE * 8 : \ (sizeof(long) > 4 ? 4 * 1024 * 1024 : PID_MAX_DEFAULT)) diff --git a/kernel/exit.c b/kernel/exit.c index 8037405..aecb48c 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -31,6 +31,7 @@ #include <linux/signal.h> #include <linux/cn_proc.h> #include <linux/mutex.h> +#include <linux/futex.h> #include <asm/uaccess.h> #include <asm/unistd.h> @@ -852,6 +853,8 @@ fastcall NORET_TYPE void do_exit(long code) exit_itimers(tsk->signal); acct_process(code); } + if (unlikely(tsk->robust_list)) + exit_robust_list(tsk); exit_mm(tsk); exit_sem(tsk); diff --git a/kernel/futex.c b/kernel/futex.c index 5efa2f9..feb724b 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -8,6 +8,10 @@ * Removed page pinning, fix privately mapped COW pages and other cleanups * (C) Copyright 2003, 2004 Jamie Lokier * + * Robust futex support started by Ingo Molnar + * (C) Copyright 2006 Red Hat Inc, All Rights Reserved + * Thanks to Thomas Gleixner for suggestions, analysis and fixes. + * * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly * enough at me, Linus for the original (flawed) idea, Matthew * Kirkwood for proof-of-concept implementation. @@ -829,6 +833,174 @@ error: goto out; } +/* + * Support for robust futexes: the kernel cleans up held futexes at + * thread exit time. + * + * Implementation: user-space maintains a per-thread list of locks it + * is holding. Upon do_exit(), the kernel carefully walks this list, + * and marks all locks that are owned by this thread with the + * FUTEX_OWNER_DEAD bit, and wakes up a waiter (if any). The list is + * always manipulated with the lock held, so the list is private and + * per-thread. Userspace also maintains a per-thread 'list_op_pending' + * field, to allow the kernel to clean up if the thread dies after + * acquiring the lock, but just before it could have added itself to + * the list. There can only be one such pending lock. + */ + +/** + * sys_set_robust_list - set the robust-futex list head of a task + * @head: pointer to the list-head + * @len: length of the list-head, as userspace expects + */ +asmlinkage long +sys_set_robust_list(struct robust_list_head __user *head, + size_t len) +{ + /* + * The kernel knows only one size for now: + */ + if (unlikely(len != sizeof(*head))) + return -EINVAL; + + current->robust_list = head; + + return 0; +} + +/** + * sys_get_robust_list - get the robust-futex list head of a task + * @pid: pid of the process [zero for current task] + * @head_ptr: pointer to a list-head pointer, the kernel fills it in + * @len_ptr: pointer to a length field, the kernel fills in the header size + */ +asmlinkage long +sys_get_robust_list(int pid, struct robust_list_head __user **head_ptr, + size_t __user *len_ptr) +{ + struct robust_list_head *head; + unsigned long ret; + + if (!pid) + head = current->robust_list; + else { + struct task_struct *p; + + ret = -ESRCH; + read_lock(&tasklist_lock); + p = find_task_by_pid(pid); + if (!p) + goto err_unlock; + ret = -EPERM; + if ((current->euid != p->euid) && (current->euid != p->uid) && + !capable(CAP_SYS_PTRACE)) + goto err_unlock; + head = p->robust_list; + read_unlock(&tasklist_lock); + } + + if (put_user(sizeof(*head), len_ptr)) + return -EFAULT; + return put_user(head, head_ptr); + +err_unlock: + read_unlock(&tasklist_lock); + + return ret; +} + +/* + * Process a futex-list entry, check whether it's owned by the + * dying task, and do notification if so: + */ +int handle_futex_death(unsigned int *uaddr, struct task_struct *curr) +{ + unsigned int futex_val; + +repeat: + if (get_user(futex_val, uaddr)) + return -1; + + if ((futex_val & FUTEX_TID_MASK) == curr->pid) { + /* + * Ok, this dying thread is truly holding a futex + * of interest. Set the OWNER_DIED bit atomically + * via cmpxchg, and if the value had FUTEX_WAITERS + * set, wake up a waiter (if any). (We have to do a + * futex_wake() even if OWNER_DIED is already set - + * to handle the rare but possible case of recursive + * thread-death.) The rest of the cleanup is done in + * userspace. + */ + if (futex_atomic_cmpxchg_inuser(uaddr, futex_val, + futex_val | FUTEX_OWNER_DIED) != + futex_val) + goto repeat; + + if (futex_val & FUTEX_WAITERS) + futex_wake((unsigned long)uaddr, 1); + } + return 0; +} + +/* + * Walk curr->robust_list (very carefully, it's a userspace list!) + * and mark any locks found there dead, and notify any waiters. + * + * We silently return on any sign of list-walking problem. + */ +void exit_robust_list(struct task_struct *curr) +{ + struct robust_list_head __user *head = curr->robust_list; + struct robust_list __user *entry, *pending; + unsigned int limit = ROBUST_LIST_LIMIT; + unsigned long futex_offset; + + /* + * Fetch the list head (which was registered earlier, via + * sys_set_robust_list()): + */ + if (get_user(entry, &head->list.next)) + return; + /* + * Fetch the relative futex offset: + */ + if (get_user(futex_offset, &head->futex_offset)) + return; + /* + * Fetch any possibly pending lock-add first, and handle it + * if it exists: + */ + if (get_user(pending, &head->list_op_pending)) + return; + if (pending) + handle_futex_death((void *)pending + futex_offset, curr); + + while (entry != &head->list) { + /* + * A pending lock might already be on the list, so + * dont process it twice: + */ + if (entry != pending) + if (handle_futex_death((void *)entry + futex_offset, + curr)) + return; + + /* + * Fetch the next entry in the list: + */ + if (get_user(entry, &entry->next)) + return; + /* + * Avoid excessively long or circular lists: + */ + if (!--limit) + break; + + cond_resched(); + } +} + long do_futex(unsigned long uaddr, int op, int val, unsigned long timeout, unsigned long uaddr2, int val2, int val3) { diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c index 1067090..d82864c 100644 --- a/kernel/sys_ni.c +++ b/kernel/sys_ni.c @@ -42,6 +42,10 @@ cond_syscall(sys_recvmsg); cond_syscall(sys_socketcall); cond_syscall(sys_futex); cond_syscall(compat_sys_futex); +cond_syscall(sys_set_robust_list); +cond_syscall(compat_sys_set_robust_list); +cond_syscall(sys_get_robust_list); +cond_syscall(compat_sys_get_robust_list); cond_syscall(sys_epoll_create); cond_syscall(sys_epoll_ctl); cond_syscall(sys_epoll_wait); |
