linux-kernel - Re: Bug 4.1.16: self-detected stall in net/unix/?

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Date:	Thu, 11 Feb 2016 15:55:42 +0000
From:	Rainer Weikusat <rweikusat@...ileactivedefense.com>
To:	Philipp Hahn <pmhahn@...ahn.de>
Cc:	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Rainer Weikusat <rweikusat@...ileactivedefense.com>,
	"David S. Miller" <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, Karolin Seeger <kseeger@...ba.org>,
	Jason Baron <jbaron@...mai.com>,
	Ben Hutchings <ben@...adent.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Arvid Requate <requate@...vention.de>,
	Stefan Gohmann <gohmann@...vention.de>
Subject: Re: Bug 4.1.16: self-detected stall in net/unix/?

Philipp Hahn <pmhahn@...ahn.de> writes:

[...]

> Probably the same bug was also reported to samba-technical by Karolin
> Seeger; she filed the bug for 3.19-ckt with Ubuntu:
>
> <https://bugs.launchpad.net/ubuntu/+source/linux-lts-trusty/+bug/1543980>
>
> Running the Samba test suite reproduces the problem; see bug for
> details.


JFTR: The oops in this bug report is for 3.13.0-77 and the patch you
reverted for 4.1 is not part of that (at least not of the upstream 3.13).


[...]

>> [  598.492559] =====================================
>> [  598.502646] [ BUG: bad unlock balance detected! ]
>> [  598.512874] 4.1.16+ #24 Not tainted
>> [  598.523134] -------------------------------------
>> [  598.533592] smbd/8659 is trying to release lock (&(&u->lock)->rlock) at:
>> [  598.544429] [<ffffffff815d1319>] spin_unlock+0x9/0x10
>> [  598.555148] but there are no more locks to release!
>> [  598.565892] 
>> [  598.565892] other info that might help us debug this:
>> [  598.586936] no locks held by smbd/8659.
>> [  598.597478] 
>> [  598.597478] stack backtrace:
>> [  598.618275] CPU: 3 PID: 8659 Comm: smbd Not tainted 4.1.16+ #24
>> [  598.628820] Hardware name: System manufacturer System Product Name/P7F-X Series, BIOS 0703    09/24/2010
>> [  598.650020]  ffffffff815d1319 ffff8800b8efbb88 ffffffff8163ee73 0000000000000000
>> [  598.661051]  ffff880034fc4110 ffff8800b8efbbb8 ffffffff810db540 ffff880034fc4110
>> [  598.671990]  ffff880034fc4110 ffff88023206bd40 ffffffff815d1319 ffff8800b8efbc08
>> [  598.682736] Call Trace:
>> [  598.693187]  [<ffffffff815d1319>] ? spin_unlock+0x9/0x10
>> [  598.703798]  [<ffffffff8163ee73>] dump_stack+0x4c/0x65
>> [  598.714223]  [<ffffffff810db540>] print_unlock_imbalance_bug+0x100/0x110
>> [  598.724611]  [<ffffffff815d1319>] ? spin_unlock+0x9/0x10
>> [  598.734763]  [<ffffffff810e0d8e>] lock_release+0x2be/0x430
>> [  598.744636]  [<ffffffff81648303>] _raw_spin_unlock+0x23/0x40
>> [  598.754230]  [<ffffffff815d41a8>] ? unix_dgram_sendmsg+0x288/0x6f0
>> [  598.763840]  [<ffffffff815d1319>] spin_unlock+0x9/0x10
>> [  598.773126]  [<ffffffff815d41e7>] unix_dgram_sendmsg+0x2c7/0x6f0
>> [  598.782209]  [<ffffffff814f6c9d>] sock_sendmsg+0x4d/0x60
>> [  598.791313]  [<ffffffff814f7c3b>] ___sys_sendmsg+0x2db/0x2f0
>> [  598.800369]  [<ffffffff812083c8>] ? kmem_cache_free+0x328/0x360
>> [  598.809383]  [<ffffffff8127c1c0>] ? locks_free_lock+0x50/0x60
>> [  598.818157]  [<ffffffff814f8649>] __sys_sendmsg+0x49/0x90
>> [  598.826742]  [<ffffffff814f86a2>] SyS_sendmsg+0x12/0x20
>> [  598.835110]  [<ffffffff816486f2>] system_call_fastpath+0x16/0x7a
>> [  598.843546] ------------[ cut here ]------------
>> [  598.851999] WARNING: CPU: 3 PID: 8659 at net/core/skbuff.c:691 skb_release_head_state+0xaa/0xb0()

Could you send your disassembled unix_dgram_sendmsg (objdump -d)? This
would be enormously helpful wrt determining which unlock is involved
here.