Subject: Re: Possible regression from "fs/exec.c: call arch_pick_mmap_layout() only once"

From: Pat Erley <[email-masked]>
Date: Thu, 02 Jan 2014 16:39:51 -0600

On 01/02/2014 04:24 PM, Richard Weinberger wrote:
> Am Donnerstag, 2. Januar 2014, 15:41:27 schrieb Pat Erley:
>> On my 64bit kernel, commit 283fe963095b38a6ab75dda1436ee66b9e45c7c2
>> seems to have broken 32bit compatibility.  I've run the bisection twice,
>> and verified that reverting this on HEAD fixes the problem.  I've
>> uploaded my .config to pastebin at http://pastebin.com/kVcr9H65
>>
>> Even this simple program:
>>
>> main(){puts("HELLO");}
>>
>> compiled with:
>>
>> gcc -m32 test.c
>>
>> Will crash with a segfault.  Stracing shows that it's failing to
>> allocate memory.
>
> Good catch!
>
> flush_old_exec() is called before setup_new_exec() and I've removed
> arch_pick_mmap_layout() from the second call site.
> Which turned out to be wrong.
>
> It is wrong because between both callers current->personality is changed.
> So, we have to remove the first call to arch_pick_mmap_layout() and keep the
> latter because only then the correct personality is set up.
>
> Can you please test your config with the following patch applied and having
> 283fe96 reverted?
>
> If it works out for you I'd send an updated patch to Andrew.
> In the meanwhile I'll double check all call sites...
>
> Thanks,
> //richard
>
> ---
> diff --git a/fs/exec.c b/fs/exec.c
> index 7ea097f..a733599 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -843,7 +843,6 @@ static int exec_mmap(struct mm_struct *mm)
>   	tsk->active_mm = mm;
>   	activate_mm(active_mm, mm);
>   	task_unlock(tsk);
> -	arch_pick_mmap_layout(mm);
>   	if (old_mm) {
>   		up_read(&old_mm->mmap_sem);
>   		BUG_ON(active_mm != old_mm);
>

Compiling right now.  Will test later tonight and let you know.

Pat