Re: [PATCH] coredump: fix pipe coredump when core limit is 0

[Jovi Zhang <bookjovi@gmail.com>]

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On Wed, Aug 24, 2011 at 6:14 PM, Jovi Zhang <bookjovi@gmail.com> wrote:
> 2011/8/23 Oleg Nesterov <oleg@redhat.com>:
>> On 08/22, Pádraig Brady wrote:
>>>
>>> On 08/21/2011 11:36 PM, Neil Horman wrote:
>>> > Concur.  The comment should be changed
>>> > Neil
>>> >
>>> > Oleg Nesterov <oleg@redhat.com> wrote:
>>> >
>>> >> On 08/21, Oleg Nesterov wrote:
>>> >>>
>>> >>> On 08/21, bookjovi@gmail.com wrote:
>>> >>>>
>>> >>>> For non-pipe case, limit 0 also means drop the coredump, so just put
>>> >>>> the zero limit check at do_coredump function begining.
>>> >>>
>>> >>> Neil, what do you think? Should we change the code or the comment?
>>> >>
>>> >> Personally I think we should fix the comment. I think RLIMIT_CORE
>>> >> doesn't apply in this case, limit == 1 check is very special. And
>>> >> this is what linux always did, except between 725eae32 and 898b374a.
>>>
>>> Sorry for jumping in late here.
>>> I would really like `ulimit -c 0` to completely disable core dumps,
>>> including not running core_pattern, as I also mentioned here:
>>> https://bugs.launchpad.net/ubuntu/+source/apport/+bug/62511
>>> I noticed this in a script where ctrl-\ was taking a long
>>> time to be registered as the core_pattern was run unconditionally.
>>
>> May be. As I said, I do not really know and personally I agree with
>> everything. My only point was, this is not the bug, this is what we
>> always did.
>>
>> This is up to Neil, I think.
>>
>> Oleg.
>>
>>
> Well, so here have two questions.
> 1) That comments "but a limit of 0 skips the dump" definitely is wrong
> right now, it don't match with reality.
> 2) In ispipe case, core limit 0 should skip the dump or not? this need
> more discussion.
>    from pipe coredump point of view, core limit is irrelevant, it
> doesn't write to file system.
>    from user point of view, there will be a lot of core files if we
> let core limit 0 create core file, user might be boring.
>
> I fix the comments part by below patch(thanks Oleg's comments), please
> use attachment patch when merge.
>

Patch attached.

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From dc7b02a1e0e413fb96d22f1d4ef4da98115cfb9d Mon Sep 17 00:00:00 2001
From: Jovi Zhang <bookjovi@gmail.com>
Date: Wed, 17 Aug 2011 15:34:29 +0800
Subject: [PATCH] coredump: fix wrong comments on core limits of pipe coredump case

In commit 898b374a, core limits recursive check vaule changed from 0 to 1,
but the corresponding comments was not changed correctly.

Signed-off-by: Jovi Zhang <bookjovi@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Neil Horman <nhorman@tuxdriver.com>
---
 fs/exec.c |   15 ++++++++-------
 1 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 25dcbe5..ba493cc 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -2158,15 +2158,16 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
 		}
 
 		if (cprm.limit == 1) {
-			/*
+			/* See umh_pipe_setup() which sets RLIMIT_CORE = 1.
+			 *
 			 * Normally core limits are irrelevant to pipes, since
 			 * we're not writing to the file system, but we use
-			 * cprm.limit of 1 here as a speacial value. Any
-			 * non-1 limit gets set to RLIM_INFINITY below, but
-			 * a limit of 0 skips the dump.  This is a consistent
-			 * way to catch recursive crashes.  We can still crash
-			 * if the core_pattern binary sets RLIM_CORE =  !1
-			 * but it runs as root, and can do lots of stupid things
+			 * cprm.limit of 1 here as a speacial value, this is a
+			 * consistent way to catch recursive crashes.
+			 * We can still crash if the core_pattern binary sets
+			 * RLIM_CORE = !1, but it runs as root, and can do
+			 * lots of stupid things.
+			 *
 			 * Note that we use task_tgid_vnr here to grab the pid
 			 * of the process group leader.  That way we get the
 			 * right pid if a thread in a multi-threaded
-- 
1.6.5.2