futex: restartable futex_wait

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>

1 files changed, 51 insertions, 5 deletions

diff --git a/kernel/futex.c b/kernel/futex.c
index 7ae2f50641ed..600bc9d801f2 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -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: