x86/vdso: Set vDSO pointer only after success

Those pointers were initialized before call to _install_special_mapping()
after the commit:

  f7b6eb3fa072 ("x86: Set context.vdso before installing the mapping")

This is not required anymore as special mappings have their vma name and
don't use arch_vma_name() after commit:

  a62c34bd2a8a ("x86, mm: Improve _install_special_mapping and fix x86 vdso naming")

So, this way to init looks less entangled.

I even belive that we can remove NULL initializers:

 - on failure load_elf_binary() will not start a new thread;
 - arch_prctl will have the same pointers as before syscall.

Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: 0x7f454c46@gmail.com
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
Cc: oleg@redhat.com
Link: http://lkml.kernel.org/r/20161027141516.28447-3-dsafonov@virtuozzo.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 23c881caabd1ce1d702ef86c0c5e2ba170283516..e739002427ed12fcbd4924d22938676643b6478e 100644 (file)
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -161,8 +161,6 @@ static int map_vdso(const struct vdso_image *image, unsigned long addr)
        }
 
        text_start = addr - image->sym_vvar_start;
-       current->mm->context.vdso = (void __user *)text_start;
-       current->mm->context.vdso_image = image;
 
        /*
         * MAYWRITE to allow gdb to COW and set breakpoints
@@ -189,14 +187,12 @@ static int map_vdso(const struct vdso_image *image, unsigned long addr)
        if (IS_ERR(vma)) {
                ret = PTR_ERR(vma);
                do_munmap(mm, text_start, image->size);
+       } else {
+               current->mm->context.vdso = (void __user *)text_start;
+               current->mm->context.vdso_image = image;
        }
 
 up_fail:
-       if (ret) {
-               current->mm->context.vdso = NULL;
-               current->mm->context.vdso_image = NULL;
-       }
-
        up_write(&mm->mmap_sem);
        return ret;
 }