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>

diff --git a/arch/tile/mm/elf.c b/arch/tile/mm/elf.c
index 23f044e..f7ddae3 100644 (file)
--- 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__