tile/elf: reorganize notify_exec()

In the future mm->exe_file will be done without mmap_sem
serialization, thus isolate and reorganize the tile elf
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.

The visible effects of this patch are:

   o We now take and drop the mmap_sem more often. Instead of
     just in arch_setup_additional_pages(), we also do it in:

     1) get_mm_exe_file()
     2) to get the mm->vm_file and notify the simulator.

    [Note that 1) will disappear once we change the locking
     rules for exe_file.]

   o We avoid getting a free page and doing d_path() while
     holding the mmap_sem. This requires reordering the checks.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com>

1 files changed, 29 insertions, 18 deletions

diff --git a/arch/tile/mm/elf.c b/arch/tile/mm/elf.c
index 23f044e8a7ab..f7ddae3725a4 100644
--- a/arch/tile/mm/elf.c
+++ b/arch/tile/mm/elf.c
@@ -17,6 +17,7 @@
 #include <linux/binfmts.h>
 #include <linux/compat.h>
 #include <linux/mman.h>
+#include <linux/file.h>
 #include <linux/elf.h>
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
@@ -39,30 +40,34 @@ static void sim_notify_exec(const char *binary_name)
 
 static int notify_exec(struct mm_struct *mm)
 {
+        int ret = 0;
         char *buf, *path;
         struct vm_area_struct *vma;
+        struct file *exe_file;
 
         if (!sim_is_simulator())
                 return 1;
 
-        if (mm->exe_file == NULL)
-                return 0;
-
-        for (vma = current->mm->mmap; ; vma = vma->vm_next) {
-                if (vma == NULL)
-                        return 0;
-                if (vma->vm_file == mm->exe_file)
-                        break;
-        }
-
         buf = (char *) __get_free_page(GFP_KERNEL);
         if (buf == NULL)
                 return 0;
 
-        path = d_path(&mm->exe_file->f_path, buf, PAGE_SIZE);
-        if (IS_ERR(path)) {
-                free_page((unsigned long)buf);
-                return 0;
+        exe_file = get_mm_exe_file(mm);
+        if (exe_file == NULL)
+                goto done_free;
+
+        path = d_path(&exe_file->f_path, buf, PAGE_SIZE);
+        if (IS_ERR(path))
+                goto done_put;
+
+        down_read(&mm->mmap_sem);
+        for (vma = current->mm->mmap; ; vma = vma->vm_next) {
+                if (vma == NULL) {
+                        up_read(&mm->mmap_sem);
+                        goto done_put;
+                }
+                if (vma->vm_file == exe_file)
+                        break;
         }
 
         /*
@@ -80,14 +85,20 @@ static int notify_exec(struct mm_struct *mm)
                         __insn_mtspr(SPR_SIM_CONTROL,
                                      (SIM_CONTROL_DLOPEN
                                       | (c << _SIM_CONTROL_OPERATOR_BITS)));
-                        if (c == '\0')
+                        if (c == '\0') {
+                                ret = 1; /* success */
                                 break;
+                        }
                 }
         }
+        up_read(&mm->mmap_sem);
 
         sim_notify_exec(path);
+done_put:
+        fput(exe_file);
+done_free:
         free_page((unsigned long)buf);
-        return 1;
+        return ret;
 }
 
 /* Notify a running simulator, if any, that we loaded an interpreter. */
@@ -109,8 +120,6 @@ int arch_setup_additional_pages(struct linux_binprm *bprm,
         struct mm_struct *mm = current->mm;
         int retval = 0;
 
-        down_write(&mm->mmap_sem);
-
         /*
          * Notify the simulator that an exec just occurred.
          * If we can't find the filename of the mapping, just use
@@ -119,6 +128,8 @@ int arch_setup_additional_pages(struct linux_binprm *bprm,
         if (!notify_exec(mm))
                 sim_notify_exec(bprm->filename);
 
+        down_write(&mm->mmap_sem);
+
         retval = setup_vdso_pages();
 
 #ifndef __tilegx__