[PATCH] mlockall() take mmap_sem a bit later

In sys_mlockall(), flags validation and can_do_mlock() check don't
require holding mmap_sem.  Move down_write() down a bit, and adjust
appropriately.
Signed-off-by: Chris Wright <chrisw@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/mlock.c

@@ -119,7 +119,7 @@ asmlinkage long sys_mlock(unsigned long start, size_t len)
 	lock_limit >>= PAGE_SHIFT;
 
 	/* check against resource limits */
-	if ( (locked <= lock_limit) || capable(CAP_IPC_LOCK))
+	if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
 		error = do_mlock(start, len, 1);
 	up_write(&current->mm->mmap_sem);
 	return error;
@@ -167,7 +167,6 @@ asmlinkage long sys_mlockall(int flags)
 	unsigned long lock_limit;
 	int ret = -EINVAL;
 
-	down_write(&current->mm->mmap_sem);
 	if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE)))
 		goto out;
 
@@ -175,6 +174,8 @@ asmlinkage long sys_mlockall(int flags)
 	if (!can_do_mlock())
 		goto out;
 
+	down_write(&current->mm->mmap_sem);
+
 	lock_limit = current->rlim[RLIMIT_MEMLOCK].rlim_cur;
 	lock_limit >>= PAGE_SHIFT;
 
@@ -182,8 +183,8 @@ asmlinkage long sys_mlockall(int flags)
 	if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
 	    capable(CAP_IPC_LOCK))
 		ret = do_mlockall(flags);
-out:
 	up_write(&current->mm->mmap_sem);
+out:
 	return ret;
 }