From mboxrd@z Thu Jan  1 00:00:00 1970
From: Julian Anastasov <ja@ssi.bg>
Subject: Re: [PATCH v2 1/2] sched: Add cond_resched_rcu_lock() helper
Date: Thu, 2 May 2013 22:24:55 +0300 (EEST)
Message-ID: <alpine.LFD.2.00.1305022211420.25417@ja.ssi.bg>
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Cc: Peter Zijlstra <peterz@infradead.org>,
	Simon Horman <horms@verge.net.au>,
	Eric Dumazet <eric.dumazet@gmail.com>,
	Ingo Molnar <mingo@redhat.com>, lvs-devel@vger.kernel.org,
	netdev@vger.kernel.org, netfilter-devel@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Pablo Neira Ayuso <pablo@netfilter.org>,
	Dipankar Sarma <dipankar@in.ibm.com>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
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	Hello,

On Thu, 2 May 2013, Julian Anastasov wrote:

> 	Note that I'm testing on some 9-year old
> UP system, i.e. 1 CPU. Now I enabled SMP to test CONFIG_TREE_RCU
> and the results are same. I think, it should be just like
> the TINY_RCU in terms of these debuggings (non-preempt). Extra 
> rcu_read_lock gives me "Illegal context switch in RCU read-side
> critical section" in addition to the "BUG: sleeping function
> called from invalid context" message.

	Just to clarify about the test with extra
rcu_read_lock because above paragraph is very confusing:

- The __might_sleep call with PREEMPT_ACTIVE | PREEMPT_RCU_OFFSET
just warns with "BUG: sleeping function called from invalid context"
because its rcu_sleep_check is silenced. We match the
nesting depth only.

- but __cond_resched -> __schedule -> schedule_debug warns about
the extra rcu_read_lock() with "BUG: scheduling while atomic" and
then with "Illegal context switch in RCU read-side critical section"
from rcu_sleep_check(0).

Regards

--
Julian Anastasov <ja@ssi.bg>