linux-kernel - __get_cpu_var() called from a preempt-unsafe context in __rcu_preempt

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]

Message-ID: <20080104120905.GA15640@in.ibm.com>
Date:	Fri, 4 Jan 2008 17:39:05 +0530
From:	Gautham R Shenoy <ego@...ibm.com>
To:	Paul E McKenney <paulmck@...ibm.com>,
	Steven Rostedt <rostedt@...dmis.org>
Cc:	"K. Prasad" <prasad@...ux.vnet.ibm.com>, mingo@...e.hu,
	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
	dipankar@...ibm.com,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Subject: __get_cpu_var() called from a preempt-unsafe context in
	__rcu_preempt_unboost() ?

Hi Paul, Steve,  

This is with reference to the preemptible rcu implementation in
2.6.24-rc5-rt1.

In __rcu_read_unlock(), we call __rcu_preempt_unboost() to unboost a
task's priority which had been bumped up when it was preempted out
while the rcu_read section.

The code path is as follows

__rcu_read_unlock()
	|
	|--> local_irq_restore(oldirq);
	|
	|--> __rcu_preempt_unboost();
		|
		|--> rcu_trace_boost_unboost_called(RCU_BOOST_ME)


where RCU_BOOST_ME is #defined as &__get_cpu_var(rcu_boost_data).

Is calling __get_cpu_var() safe in this context, since we've already
enabled the local interrupts and we're not in a preempt_disabled() ?

Thanks and Regards
gautham.

-- 
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"
--
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/