futex: reduce mmap_sem usage

now that we rely on get_user_pages() for the shared key handling
move all the mmap_sem stuff closely around the slow paths.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 4 insertions, 79 deletions

diff --git a/kernel/futex.c b/kernel/futex.c
index a4c39fa0a7a3..6a726684217e 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -123,24 +123,6 @@ struct futex_hash_bucket {
 static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
 
 /*
- * Take mm->mmap_sem, when futex is shared
- */
-static inline void futex_lock_mm(struct rw_semaphore *fshared)
-{
-        if (fshared)
-                down_read(fshared);
-}
-
-/*
- * Release mm->mmap_sem, when the futex is shared
- */
-static inline void futex_unlock_mm(struct rw_semaphore *fshared)
-{
-        if (fshared)
-                up_read(fshared);
-}
-
-/*
  * We hash on the keys returned from get_futex_key (see below).
  */
 static struct futex_hash_bucket *hash_futex(union futex_key *key)
@@ -250,7 +232,9 @@ static int get_futex_key(u32 __user *uaddr, struct rw_semaphore *fshared,
         }
 
 again:
+        down_read(&mm->mmap_sem);
         err = get_user_pages(current, mm, address, 1, 0, 0, &page, NULL);
+        up_read(&mm->mmap_sem);
         if (err < 0)
                 return err;
 
@@ -327,8 +311,7 @@ static int futex_handle_fault(unsigned long address,
         if (attempt > 2)
                 return ret;
 
-        if (!fshared)
-                down_read(&mm->mmap_sem);
+        down_read(&mm->mmap_sem);
         vma = find_vma(mm, address);
         if (vma && address >= vma->vm_start &&
             (vma->vm_flags & VM_WRITE)) {
@@ -348,8 +331,7 @@ static int futex_handle_fault(unsigned long address,
                                 current->min_flt++;
                 }
         }
-        if (!fshared)
-                up_read(&mm->mmap_sem);
+        up_read(&mm->mmap_sem);
         return ret;
 }
 
@@ -719,8 +701,6 @@ static int futex_wake(u32 __user *uaddr, struct rw_semaphore *fshared,
         if (!bitset)
                 return -EINVAL;
 
-        futex_lock_mm(fshared);
-
         ret = get_futex_key(uaddr, fshared, &key);
         if (unlikely(ret != 0))
                 goto out;
@@ -749,7 +729,6 @@ static int futex_wake(u32 __user *uaddr, struct rw_semaphore *fshared,
         spin_unlock(&hb->lock);
 out:
         put_futex_key(fshared, &key);
-        futex_unlock_mm(fshared);
         return ret;
 }
 
@@ -769,8 +748,6 @@ futex_wake_op(u32 __user *uaddr1, struct rw_semaphore *fshared,
         int ret, op_ret, attempt = 0;
 
 retryfull:
-        futex_lock_mm(fshared);
-
         ret = get_futex_key(uaddr1, fshared, &key1);
         if (unlikely(ret != 0))
                 goto out;
@@ -821,12 +798,6 @@ retry:
                         goto retry;
                 }
 
-                /*
-                 * If we would have faulted, release mmap_sem,
-                 * fault it in and start all over again.
-                 */
-                futex_unlock_mm(fshared);
-
                 ret = get_user(dummy, uaddr2);
                 if (ret)
                         return ret;
@@ -864,7 +835,6 @@ retry:
 out:
         put_futex_key(fshared, &key2);
         put_futex_key(fshared, &key1);
-        futex_unlock_mm(fshared);
 
         return ret;
 }
@@ -884,8 +854,6 @@ static int futex_requeue(u32 __user *uaddr1, struct rw_semaphore *fshared,
         int ret, drop_count = 0;
 
  retry:
-        futex_lock_mm(fshared);
-
         ret = get_futex_key(uaddr1, fshared, &key1);
         if (unlikely(ret != 0))
                 goto out;
@@ -908,12 +876,6 @@ static int futex_requeue(u32 __user *uaddr1, struct rw_semaphore *fshared,
                         if (hb1 != hb2)
                                 spin_unlock(&hb2->lock);
 
-                        /*
-                         * If we would have faulted, release mmap_sem, fault
-                         * it in and start all over again.
-                         */
-                        futex_unlock_mm(fshared);
-
                         ret = get_user(curval, uaddr1);
 
                         if (!ret)
@@ -967,7 +929,6 @@ out_unlock:
 out:
         put_futex_key(fshared, &key2);
         put_futex_key(fshared, &key1);
-        futex_unlock_mm(fshared);
         return ret;
 }
 
@@ -1211,8 +1172,6 @@ static int futex_wait(u32 __user *uaddr, struct rw_semaphore *fshared,
         q.pi_state = NULL;
         q.bitset = bitset;
  retry:
-        futex_lock_mm(fshared);
-
         q.key = FUTEX_KEY_INIT;
         ret = get_futex_key(uaddr, fshared, &q.key);
         if (unlikely(ret != 0))
@@ -1245,12 +1204,6 @@ static int futex_wait(u32 __user *uaddr, struct rw_semaphore *fshared,
         if (unlikely(ret)) {
                 queue_unlock(&q, hb);
 
-                /*
-                 * If we would have faulted, release mmap_sem, fault it in and
-                 * start all over again.
-                 */
-                futex_unlock_mm(fshared);
-
                 ret = get_user(uval, uaddr);
 
                 if (!ret)
@@ -1265,12 +1218,6 @@ static int futex_wait(u32 __user *uaddr, struct rw_semaphore *fshared,
         queue_me(&q, hb);
 
         /*
-         * Now the futex is queued and we have checked the data, we
-         * don't want to hold mmap_sem while we sleep.
-         */
-        futex_unlock_mm(fshared);
-
-        /*
          * There might have been scheduling since the queue_me(), as we
          * cannot hold a spinlock across the get_user() in case it
          * faults, and we cannot just set TASK_INTERRUPTIBLE state when
@@ -1355,7 +1302,6 @@ static int futex_wait(u32 __user *uaddr, struct rw_semaphore *fshared,
 
  out_release_sem:
         put_futex_key(fshared, &q.key);
-        futex_unlock_mm(fshared);
         return ret;
 }
 
@@ -1404,8 +1350,6 @@ static int futex_lock_pi(u32 __user *uaddr, struct rw_semaphore *fshared,
 
         q.pi_state = NULL;
  retry:
-        futex_lock_mm(fshared);
-
         q.key = FUTEX_KEY_INIT;
         ret = get_futex_key(uaddr, fshared, &q.key);
         if (unlikely(ret != 0))
@@ -1495,7 +1439,6 @@ static int futex_lock_pi(u32 __user *uaddr, struct rw_semaphore *fshared,
                          * exit to complete.
                          */
                         queue_unlock(&q, hb);
-                        futex_unlock_mm(fshared);
                         cond_resched();
                         goto retry;
 
@@ -1527,12 +1470,6 @@ static int futex_lock_pi(u32 __user *uaddr, struct rw_semaphore *fshared,
          */
         queue_me(&q, hb);
 
-        /*
-         * Now the futex is queued and we have checked the data, we
-         * don't want to hold mmap_sem while we sleep.
-         */
-        futex_unlock_mm(fshared);
-
         WARN_ON(!q.pi_state);
         /*
          * Block on the PI mutex:
@@ -1545,7 +1482,6 @@ static int futex_lock_pi(u32 __user *uaddr, struct rw_semaphore *fshared,
                 ret = ret ? 0 : -EWOULDBLOCK;
         }
 
-        futex_lock_mm(fshared);
         spin_lock(q.lock_ptr);
 
         if (!ret) {
@@ -1611,7 +1547,6 @@ static int futex_lock_pi(u32 __user *uaddr, struct rw_semaphore *fshared,
 
         /* Unqueue and drop the lock */
         unqueue_me_pi(&q);
-        futex_unlock_mm(fshared);
 
         if (to)
                 destroy_hrtimer_on_stack(&to->timer);
@@ -1622,7 +1557,6 @@ static int futex_lock_pi(u32 __user *uaddr, struct rw_semaphore *fshared,
 
  out_release_sem:
         put_futex_key(fshared, &q.key);
-        futex_unlock_mm(fshared);
         if (to)
                 destroy_hrtimer_on_stack(&to->timer);
         return ret;
@@ -1646,8 +1580,6 @@ static int futex_lock_pi(u32 __user *uaddr, struct rw_semaphore *fshared,
                 goto retry_unlocked;
         }
 
-        futex_unlock_mm(fshared);
-
         ret = get_user(uval, uaddr);
         if (!ret && (uval != -EFAULT))
                 goto retry;
@@ -1679,10 +1611,6 @@ retry:
          */
         if ((uval & FUTEX_TID_MASK) != task_pid_vnr(current))
                 return -EPERM;
-        /*
-         * First take all the futex related locks:
-         */
-        futex_lock_mm(fshared);
 
         ret = get_futex_key(uaddr, fshared, &key);
         if (unlikely(ret != 0))
@@ -1742,7 +1670,6 @@ out_unlock:
         spin_unlock(&hb->lock);
 out:
         put_futex_key(fshared, &key);
-        futex_unlock_mm(fshared);
 
         return ret;
 
@@ -1766,8 +1693,6 @@ pi_faulted:
                 goto retry_unlocked;
         }
 
-        futex_unlock_mm(fshared);
-
         ret = get_user(uval, uaddr);
         if (!ret && (uval != -EFAULT))
                 goto retry;