linux-kernel - [PATCH 2/2] x86/vdso: set vdso pointer only after success

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Date:   Thu, 27 Oct 2016 17:15:16 +0300
From:   Dmitry Safonov <dsafonov@...tuozzo.com>
To:     <linux-kernel@...r.kernel.org>
CC:     Dmitry Safonov <dsafonov@...tuozzo.com>, <0x7f454c46@...il.com>,
        "Cyrill Gorcunov" <gorcunov@...nvz.org>,
        Andy Lutomirski <luto@...nel.org>, <oleg@...hat.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, <linux-mm@...ck.org>,
        <x86@...nel.org>
Subject: [PATCH 2/2] 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, 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.

Cc: 0x7f454c46@...il.com
Cc: Cyrill Gorcunov <gorcunov@...nvz.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: oleg@...hat.com
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: linux-mm@...ck.org
Cc: x86@...nel.org
Signed-off-by: Dmitry Safonov <dsafonov@...tuozzo.com>
---
 arch/x86/entry/vdso/vma.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 23c881caabd1..e739002427ed 100644
--- 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;
 }
-- 
2.10.1