linux-kernel - Re: call_rcu from trace

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 17 Jun 2015 11:39:29 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Daniel Wagner <daniel.wagner@...-carit.de>,
	paulmck@...ux.vnet.ibm.com
CC:	LKML <linux-kernel@...r.kernel.org>, rostedt@...dmis.org
Subject: Re: call_rcu from trace_preempt

On 6/17/15 2:05 AM, Daniel Wagner wrote:
>> >Steven's suggestion deferring the work via irq_work results in the same
>> >stack trace. (Now I get cold feets, without the nice heat from the CPU
>> >busy looping...)
> That one still not working. It also makes the system really really slow.
> I guess I still do something completely wrong.

tried your irq_work patch. It indeed makes the whole system
unresponsive. Ctrl-C of hwlathist no longer works and
it runs out of memory in 20 sec or so of running hwlathist
on idle system (without parallel hackbench).
It looks that free_pending flag is racy, so I removed it,
but it didn't help.

Also I've tried all sort of other things in rcu including
add rcu_bpf similar to rcu_sched to make sure that recursive
call into call_rcu will not be messing rcu_preempt or rcu_sched
states and instead will be operating on rcu_bpf per-cpu states.
In theory that should have worked flawlessly and it sort-of did.
But multiple hackbench runs still managed to crash it.
So far I think the temp workaround is to stick with array maps
for probing such low level things like trace_preempt.
Note that pre-allocation of all elements in hash map also won't
help, since the problem here is some collision of call_rcu and
rcu_process_callbacks. I'm pretty sure that kfree_rcu with
rcu_is_watching patch is ready for this type of abuse.
The rcu_process_callbacks() path - no yet. I'm still analyzing it.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/