linux-kernel - [PATCH 3.1-rc8 0/2] Two false positives from debugging tools (lockdep, kmemleak)

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Message-ID: <20110930014334.GA2368@elie.chipublib.org>
Date:	Thu, 29 Sep 2011 20:43:34 -0500
From:	Jonathan Nieder <jrnieder@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nelson Elhage <nelhage@...hage.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Catalin Marinas <catalin.marinas@....com>
Subject: [PATCH 3.1-rc8 0/2] Two false positives from debugging tools
 (lockdep, kmemleak)

Hi,

Especially during the -rc period, it is nice to be able to take
advantage of lockdep and kmemleak to find bugs.  False positives make
it harder to find real problems amid the noise.

At boot time, I get:

| allocated 14680064 bytes of page_cgroup
| please try 'cgroup_disable=memory' option if you don't want memory cgroups
| kmemleak: Trying to color unknown object at 0xffff88006f500000 as Grey
| Pid: 0, comm: swapper Not tainted 3.1.0-rc8-00031-gd5767c53535a #12
| Call Trace:
|  [<ffffffff810f8637>] paint_ptr+0x56/0x8e
|  [<ffffffff812e336c>] kmemleak_not_leak+0x23/0x42
|  [<ffffffff816a00d5>] kmemleak_init+0x1db/0x23a
|  [<ffffffff81686ad2>] start_kernel+0x31c/0x3b1
|  [<ffffffff816862a8>] x86_64_start_reservations+0xaf/0xb3
|  [<ffffffff81686140>] ? early_idt_handlers+0x140/0x140
|  [<ffffffff816863ae>] x86_64_start_kernel+0x102/0x111
| kmemleak: Trying to color unknown object at 0xffff88006f600000 as Grey
[and so on, for 13 addresses in all]

Also:

| [  222.425445] systemd-logind/908 is trying to acquire lock:
| [  222.425447]  (&ep->mtx){+.+.+.}, at: [<ffffffff8112da68>] ep_scan_ready_list+0x3c/0x1a7
| [  222.425456] 
| [  222.425457] but task is already holding lock:
| [  222.425459]  (&ep->mtx){+.+.+.}, at: [<ffffffff8112dfd8>] sys_epoll_ctl+0x11d/0x520

Luckily both false positives seem to be known and well understood.
The first of the patches below (the kmemleak one) seems to have fallen
under the radar --- I can't even find it in linux-next.  The second (the
lockdep one) is taken from akpm's -mm patchset.

Thoughts?

Nelson Elhage (1):
  epoll: fix spurious lockdep warnings

Steven Rostedt (1):
  cgroup/kmemleak: Annotate alloc_page() for cgroup allocations

 fs/eventpoll.c   |   25 ++++++++++++++++++-------
 mm/page_cgroup.c |    7 +++++--
 2 files changed, 23 insertions(+), 9 deletions(-)

-- 
1.7.7.rc1

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