Date:	Fri, 02 Mar 2007 13:41:30 +0900
From:	"Kawai, Hidehiro" <hidehiro.kawai.ez@...achi.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	kernel list <linux-kernel@...r.kernel.org>
Cc:	Pavel Machek <pavel@....cz>, Robin Holt <holt@....com>,
	David Howells <dhowells@...hat.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	sugita <yumiko.sugita.yf@...achi.com>,
	Satoshi OSHIMA <soshima@...hat.com>,
	Hideo AOKI <haoki@...hat.com>
Subject: [PATCH 0/4] coredump: core dump masking support v4

Hi,

This patch series is version 4 of the core dump masking feature,
which provides a per-process flag not to dump anonymous shared
memory segments.

In the previous version, the flag value was passed around the core
dump functions as an argument to use the same setting while dumping.
In this version, instead of doing that, a r/w semaphore prevents the
setting from being changed while dumping.

This patch series can be applied against 2.6.20-mm2.
The supported core file formats are ELF and ELF-FDPIC. ELF has been
tested, but ELF-FDPIC has not been built and tested because I don't
have the test environment.


Background:
Some software programs share huge memory among hundreds of
processes. If a failure occurs on one of these processes, they can
be signaled by a monitoring process to generate core files and
restart the service. However, it can develop into a system-wide
failure such as system slow down for a long time and disk space
shortage because the total size of the core files is very huge!

To avoid the above situation we can limit the core file size by
setrlimit(2) or ulimit(1). But this method can lose important data
such as stack because core dumping is terminated halfway.
So I suggest keeping shared memory segments from being dumped for
particular processes. Because the shared memory attached to processes
is common in them, we don't need to dump the shared memory every time.


Usage:
Get all shared memory segments of pid 1234 not to dump:

  $ echo 1 > /proc/1234/coredump_omit_anonymous_shared

When a new process is created, the process inherits the flag status
from its parent. It is useful to set the core dump flags before the
program runs. For example:

  $ echo 1 > /proc/self/coredump_omit_anonymous_shared
  $ ./some_program


ChangeLog:
v4:
  - in maydump(), retrieve the core dump setting from mm_struct
    directly, instead of its additional argument
  - writing to /proc/<pid>/coredump_omit_anonymous_shared returns
    EBUSY while core dumping.

v3:
http://groups.google.com/group/linux.kernel/browse_frm/thread/706d2ae41c1cb2de/
  - remove `/proc/<pid>/core_flags' proc entry
  - add `/proc/<pid>/coredump_anonymous_shared' as a named flag
  - remove kernel.core_flags_enable sysctl parameter

v2:
http://groups.google.com/group/linux.kernel/browse_frm/thread/cb254465971d4a42/
http://groups.google.com/group/linux.kernel/browse_frm/thread/da78f2702e06fa11/
  - rename `coremask' to `core_flags'
  - change `core_flags' member in mm_struct to a bit field
    next to `dumpable'
  - introduce a global spin lock to protect adjacent two bit fields
    (core_flags and dumpable) from race condition
  - fix a bug that the generated core file can be corrupted when
    core dumping and updating core_flags occur concurrently
  - add kernel.core_flags_enable sysctl parameter to enable/disable
    flags in /proc/<pid>/core_flags
  - support ELF-FDPIC binary format, but not tested

v1:
http://groups.google.com/group/linux.kernel/browse_frm/thread/1381fc54d716e3e6/

-- 
Hidehiro Kawai
Hitachi, Ltd., Systems Development Laboratory
E-mail: hidehiro.kawai.ez@...achi.com

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