futex: restartable futex_wait
Nick Piggin [Tue, 8 May 2007 07:26:43 +0000 (00:26 -0700)]
LTP test sigaction_16_24 fails, because it expects sem_wait to be restarted
if SA_RESTART is set.  sem_wait is implemented with futex_wait, that
currently doesn't support being restarted.  Ulrich confirms that the call
should be restartable.

Implement a restart_block method to handle the relative timeout, and allow
restarts.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Ulrich Drepper <drepper@redhat.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Roland McGrath <roland@redhat.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/futex.c

index 7ae2f50..600bc9d 100644 (file)
@@ -980,12 +980,15 @@ static void unqueue_me_pi(struct futex_q *q, struct futex_hash_bucket *hb)
        drop_futex_key_refs(&q->key);
 }
 
-static int futex_wait(u32 __user *uaddr, u32 val, unsigned long time)
+static long futex_wait_restart(struct restart_block *restart);
+static int futex_wait_abstime(u32 __user *uaddr, u32 val,
+                       int timed, unsigned long abs_time)
 {
        struct task_struct *curr = current;
        DECLARE_WAITQUEUE(wait, curr);
        struct futex_hash_bucket *hb;
        struct futex_q q;
+       unsigned long time_left = 0;
        u32 uval;
        int ret;
 
@@ -1065,8 +1068,21 @@ static int futex_wait(u32 __user *uaddr, u32 val, unsigned long time)
         * !list_empty() is safe here without any lock.
         * q.lock_ptr != 0 is not safe, because of ordering against wakeup.
         */
-       if (likely(!list_empty(&q.list)))
-               time = schedule_timeout(time);
+       time_left = 0;
+       if (likely(!list_empty(&q.list))) {
+               unsigned long rel_time;
+
+               if (timed) {
+                       unsigned long now = jiffies;
+                       if (time_after(now, abs_time))
+                               rel_time = 0;
+                       else
+                               rel_time = abs_time - now;
+               } else
+                       rel_time = MAX_SCHEDULE_TIMEOUT;
+
+               time_left = schedule_timeout(rel_time);
+       }
        __set_current_state(TASK_RUNNING);
 
        /*
@@ -1077,13 +1093,25 @@ static int futex_wait(u32 __user *uaddr, u32 val, unsigned long time)
        /* If we were woken (and unqueued), we succeeded, whatever. */
        if (!unqueue_me(&q))
                return 0;
-       if (time == 0)
+       if (time_left == 0)
                return -ETIMEDOUT;
+
        /*
         * We expect signal_pending(current), but another thread may
         * have handled it for us already.
         */
-       return -EINTR;
+       if (time_left == MAX_SCHEDULE_TIMEOUT)
+               return -ERESTARTSYS;
+       else {
+               struct restart_block *restart;
+               restart = &current_thread_info()->restart_block;
+               restart->fn = futex_wait_restart;
+               restart->arg0 = (unsigned long)uaddr;
+               restart->arg1 = (unsigned long)val;
+               restart->arg2 = (unsigned long)timed;
+               restart->arg3 = abs_time;
+               return -ERESTART_RESTARTBLOCK;
+       }
 
  out_unlock_release_sem:
        queue_unlock(&q, hb);
@@ -1093,6 +1121,24 @@ static int futex_wait(u32 __user *uaddr, u32 val, unsigned long time)
        return ret;
 }
 
+static int futex_wait(u32 __user *uaddr, u32 val, unsigned long rel_time)
+{
+       int timed = (rel_time != MAX_SCHEDULE_TIMEOUT);
+       return futex_wait_abstime(uaddr, val, timed, jiffies+rel_time);
+}
+
+static long futex_wait_restart(struct restart_block *restart)
+{
+       u32 __user *uaddr = (u32 __user *)restart->arg0;
+       u32 val = (u32)restart->arg1;
+       int timed = (int)restart->arg2;
+       unsigned long abs_time = restart->arg3;
+
+       restart->fn = do_no_restart_syscall;
+       return (long)futex_wait_abstime(uaddr, val, timed, abs_time);
+}
+
+
 /*
  * Userspace tried a 0 -> TID atomic transition of the futex value
  * and failed. The kernel side here does the whole locking operation: