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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2011-10-05 11:45:18 -0700
committerClark Williams <williams@redhat.com>2012-04-13 11:01:43 -0500
commit9bfb4daf32ad9a659fdcaa405f3a47e426da3cf7 (patch)
tree6a5121e7d81d8461dca41c28a7b9ec8823dcbd90 /include/linux
parent876e9b8f884558427902a43eae111bf45f632b14 (diff)
rcu: Make ksoftirqd do RCU quiescent states
Implementing RCU-bh in terms of RCU-preempt makes the system vulnerable to network-based denial-of-service attacks. This patch therefore makes __do_softirq() invoke rcu_bh_qs(), but only when __do_softirq() is running in ksoftirqd context. A wrapper layer in interposed so that other calls to __do_softirq() avoid invoking rcu_bh_qs(). The underlying function __do_softirq_common() does the actual work. The reason that rcu_bh_qs() is bad in these non-ksoftirqd contexts is that there might be a local_bh_enable() inside an RCU-preempt read-side critical section. This local_bh_enable() can invoke __do_softirq() directly, so if __do_softirq() were to invoke rcu_bh_qs() (which just calls rcu_preempt_qs() in the PREEMPT_RT_FULL case), there would be an illegal RCU-preempt quiescent state in the middle of an RCU-preempt read-side critical section. Therefore, quiescent states can only happen in cases where __do_softirq() is invoked directly from ksoftirqd. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/20111005184518.GA21601@linux.vnet.ibm.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'include/linux')
-rw-r--r--include/linux/rcupdate.h6
1 files changed, 0 insertions, 6 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 888d24ac66ba..aaf8b7dc360c 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -194,13 +194,7 @@ static inline int rcu_preempt_depth(void)
/* Internal to kernel */
extern void rcu_sched_qs(int cpu);
-
-#ifndef CONFIG_PREEMPT_RT_FULL
extern void rcu_bh_qs(int cpu);
-#else
-static inline void rcu_bh_qs(int cpu) { }
-#endif
-
extern void rcu_check_callbacks(int cpu, int user);
struct notifier_block;
extern void rcu_idle_enter(void);