linux-kernel - Re: [PATCH tip/core/rcu 0/2] rcu: fixes for RCU lockdep

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Message-ID: <20100227125953.GA15880@elte.hu>
Date:	Sat, 27 Feb 2010 13:59:53 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	dvhltc@...ibm.com, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com
Subject: Re: [PATCH tip/core/rcu 0/2] rcu: fixes for RCU lockdep


here's another one:

[    0.000000] Memory: 914996k/1047744k available (15146k kernel code, 452k absent, 131584k reserved, 12516k data, 2552k init)
[    0.000000] SLUB: Genslabs=13, HWalign=64, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
[    0.000000] 
[    0.000000] ===================================================
[    0.000000] [ INFO: suspicious rcu_dereference_check() usage. ]
[    0.000000] ---------------------------------------------------
[    0.000000] include/linux/cgroup.h:492 invoked rcu_dereference_check() without protection!
[    0.000000] 
[    0.000000] other info that might help us debug this:
[    0.000000] 
[    0.000000] 1 lock held by swapper/0:
[    0.000000]  #0:  (&rq->lock){......}, at: [<ffffffff81ec0bad>] init_idle+0x31/0x1ee
[    0.000000] 
[    0.000000] stack backtrace:
[    0.000000] Pid: 0, comm: swapper Not tainted 2.6.33-tip+ #10563
[    0.000000] Call Trace:
[    0.000000]  [<ffffffff810ad1c1>] lockdep_rcu_dereference+0xa1/0xb0
[    0.000000]  [<ffffffff81ec0cbd>] init_idle+0x141/0x1ee
[    0.000000]  [<ffffffff82ceff40>] sched_init+0x43a/0x4b6
[    0.000000]  [<ffffffff82cdcceb>] start_kernel+0x1b3/0x49e
[    0.000000]  [<ffffffff82cdc319>] x86_64_start_reservations+0x120/0x124
[    0.000000]  [<ffffffff82cdc46b>] x86_64_start_kernel+0x14e/0x15d
[    0.000000] Hierarchical RCU implementation.
[    0.000000] RCU-based detection of stalled CPUs is enabled.
[    0.000000] NR_IRQS:4352

on:

1bc9767: Merge branch 'tracing/core'

Config attached. This too seems to a sched-init artifact. Could we use 
inc_preempt_count() perhaps to make sure we have the preempt count disabled 
even on !PREEMPT? Instead of hacking more 'the scheduler is not initialized 
yet' checks into various debug checks?

	Ingo

View attachment "config" of type "text/plain" (66928 bytes)