linux-kernel - Re: [PATCH v2] [RFC] tracepoint: Add signal coredump tracepoint

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Date:	Mon, 07 Dec 2009 10:25:48 -0500
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	lkml <linux-kernel@...r.kernel.org>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>,
	Oleg Nesterov <oleg@...hat.com>,
	Roland McGrath <roland@...hat.com>,
	Jason Baron <jbaron@...hat.com>
Subject: Re: [PATCH v2] [RFC] tracepoint: Add signal coredump tracepoint

KOSAKI Motohiro wrote:
> 2009/12/3 Masami Hiramatsu<mhiramat@...hat.com>:
>> Add signal coredump tracepoint which shows signal number,
>> mm->flags, limits, pointer to file structure and core
>> file name.
>>
>> This tracepoint requirement comes mainly from the viewpoint of
>> administrators. Since now we have introduced many coredump
>> configurations (e.g. dumpable, coredump_filter, core_pattern,
>> etc) and some of them can be modified by users, it will be hard
>> to know what was actually dumped (or not dumped) after some
>> problem happened on the system. For example, a process didn't
>> generated core, coredump doesn't have some sections, etc.
>> In those cases, the coredump tracepoint can help us to know
>> why the core file is so big or small, or not generated, by
>> recording all configurations for all processes on the system.
>> That will reduce system-administration cost.
>
> AFAIK, not-dumped case is important than dump successful case.
> IOW, admin need to know why the crashed process was not dumped.

Certainly, failure cases are important, but also, the cases
that dumped-core doesn't or does include some sections
are also important.

> This tracepoint doesn't cover all failure case. especially
> binfmt->core_dump() et.al.
> IOW, this tracepoint seems too specialized piped-coredump feature.

Hmm, so would you mean that after calling binfmt->core_dump()
is better place?

> What do you think this tracepoint's use case?

Frankly to say, our first attempt was tracing mm->flags because
it can be changed by users without asking, and they sometimes
ask why core is not perfect or why core file is so big.

Perhaps, covering all of those failure cases and succeed cases,
gives better information for them. In that case, we might better
tweak execution(goto) path to leave some error code on retval.

e.g.
         if (IS_ERR(file))
                 goto fail_dropcount;
+	retval = -EBADF;
         inode = file->f_path.dentry->d_inode;
         if (inode->i_nlink > 1)
                 goto close_fail;        /* multiple links - don't dump */
         if (!ispipe && d_unhashed(file->f_path.dentry))
                 goto close_fail;

         /* AK: actually i see no reason to not allow this for named pipes etc.,
            but keep the previous behaviour for now. */
         if (!ispipe && !S_ISREG(inode->i_mode))
                 goto close_fail;
         /*
          * Dont allow local users get cute and trick others to coredump
          * into their pre-created files:
          */
+	retval = -EPERM;
         if (inode->i_uid != current_fsuid())
                 goto close_fail;
+	retval = -EINVAL;
         if (!file->f_op)
                 goto close_fail;
         if (!file->f_op->write)
                 goto close_fail;
+	retval = -EEXIST;
         if (!ispipe && do_truncate(file->f_path.dentry, 0, 0, file) != 0)
                 goto close_fail;


Thank you,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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