linux-kernel - Re: [PATCH 2/2] fs, elf: drop MAP_FIXED usage from elf

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Message-ID: <20180418115546.GZ17484@dhcp22.suse.cz>
Date:   Wed, 18 Apr 2018 13:55:46 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] fs, elf: drop MAP_FIXED usage from elf_map

On Wed 18-04-18 20:43:11, Tetsuo Handa wrote:
> Michal Hocko wrote:
> > > Don't complain if IS_ERR_VALUE(),
> > 
> > this is simply wrong. We do want to warn on the failure because this is
> > when the actual clash happens. We should just warn on EEXIST.
> 
> >From 25442cdd31aa5cc8522923a0153a77dfd2ebc832 Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Date: Wed, 18 Apr 2018 20:38:15 +0900
> Subject: [PATCH] fs, elf: don't complain MAP_FIXED_NOREPLACE unless -EEXIST
>  error.
> 
> Commit 4ed28639519c7bad ("fs, elf: drop MAP_FIXED usage from elf_map") is
> printing spurious messages under memory pressure due to map_addr == -ENOMEM.
> 
>  9794 (a.out): Uhuuh, elf segment at 00007f2e34738000(fffffffffffffff4) requested but the memory is mapped already
>  14104 (a.out): Uhuuh, elf segment at 00007f34fd76c000(fffffffffffffff4) requested but the memory is mapped already
>  16843 (a.out): Uhuuh, elf segment at 00007f930ecc7000(fffffffffffffff4) requested but the memory is mapped already
> 
> Complain only if -EEXIST, and use %px for printing the address.

Yes this is better. But...

[...]
> -	if ((type & MAP_FIXED_NOREPLACE) && BAD_ADDR(map_addr))
> -		pr_info("%d (%s): Uhuuh, elf segment at %p requested but the memory is mapped already\n",
> -				task_pid_nr(current), current->comm,
> -				(void *)addr);
> +	if ((type & MAP_FIXED_NOREPLACE) && map_addr == -EEXIST)

... please use PTR_ERR(map_addr) == -EEXIST

then you can add 
Acked-by: Michal Hocko <mhocko@...e.com>

> +		pr_info("%d (%s): Uhuuh, elf segment at %px requested but the memory is mapped already\n",
> +			task_pid_nr(current), current->comm, (void *)addr);
>  
>  	return(map_addr);
>  }
> -- 
> 1.8.3.1

-- 
Michal Hocko
SUSE Labs