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

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Message-Id: <201804182043.JFH90161.LStOOMFFOJQHVF@I-love.SAKURA.ne.jp>
Date:   Wed, 18 Apr 2018 20:43:11 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     mhocko@...nel.org
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

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.

Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Andrei Vagin <avagin@...nvz.org>
Cc: Khalid Aziz <khalid.aziz@...cle.com>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Kees Cook <keescook@...omium.org>
Cc: Abdul Haleem <abdhalee@...ux.vnet.ibm.com>
Cc: Joel Stanley <joel@....id.au>
Cc: Anshuman Khandual <khandual@...ux.vnet.ibm.com>
---
 fs/binfmt_elf.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 41e0418..96615d9 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -377,10 +377,9 @@ static unsigned long elf_map(struct file *filep, unsigned long addr,
 	} else
 		map_addr = vm_mmap(filep, addr, size, prot, type, off);
 
-	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)
+		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