powerpc/oprofile: reduce mmap_sem hold for exe_file

In the future mm->exe_file will be done without mmap_sem serialization,
thus isolate and reorganize the related code to make the transition
easier.  Good users will, make use of the more standard get_mm_exe_file(),
requiring only holding the mmap_sem to read the value, and relying on
reference counting to make sure that the exe file won't dissappear
underneath us while getting the dcookie.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Robert Richter <rric@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/powerpc/oprofile/cell/spu_task_sync.c

@@ -22,6 +22,7 @@
 #include <linux/kref.h>
 #include <linux/mm.h>
 #include <linux/fs.h>
+#include <linux/file.h>
 #include <linux/module.h>
 #include <linux/notifier.h>
 #include <linux/numa.h>
@@ -322,18 +323,20 @@ get_exec_dcookie_and_offset(struct spu *spu, unsigned int *offsetp,
 	unsigned long app_cookie = 0;
 	unsigned int my_offset = 0;
 	struct vm_area_struct *vma;
+	struct file *exe_file;
 	struct mm_struct *mm = spu->mm;
 
 	if (!mm)
 		goto out;
 
-	down_read(&mm->mmap_sem);
-
-	if (mm->exe_file) {
-		app_cookie = fast_get_dcookie(&mm->exe_file->f_path);
-		pr_debug("got dcookie for %pD\n", mm->exe_file);
+	exe_file = get_mm_exe_file(mm);
+	if (exe_file) {
+		app_cookie = fast_get_dcookie(&exe_file->f_path);
+		pr_debug("got dcookie for %pD\n", exe_file);
+		fput(exe_file);
 	}
 
+	down_read(&mm->mmap_sem);
 	for (vma = mm->mmap; vma; vma = vma->vm_next) {
 		if (vma->vm_start > spu_ref || vma->vm_end <= spu_ref)
 			continue;