diff options
| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2011-10-05 11:45:18 -0700 |
|---|---|---|
| committer | Steven Rostedt <rostedt@goodmis.org> | 2013-11-13 11:21:15 -0500 |
| commit | 8311747132db0b74aaef3708a4f381d6a3b506f4 (patch) | |
| tree | 4d347502353ee3a496fe1cdf260e2a8baae368ef /kernel/softirq.c | |
| parent | 18f0582b9c660aad2fc1af47fab78f610fed1fb0 (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 'kernel/softirq.c')
| -rw-r--r-- | kernel/softirq.c | 20 |
1 files changed, 13 insertions, 7 deletions
diff --git a/kernel/softirq.c b/kernel/softirq.c index fdd1a4d9c8b4..04e4a5ff774f 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -142,7 +142,7 @@ static void wakeup_softirqd(void) wake_up_process(tsk); } -static void handle_pending_softirqs(u32 pending, int cpu) +static void handle_pending_softirqs(u32 pending, int cpu, int need_rcu_bh_qs) { struct softirq_action *h = softirq_vec; unsigned int prev_count = preempt_count(); @@ -165,7 +165,8 @@ static void handle_pending_softirqs(u32 pending, int cpu) prev_count, (unsigned int) preempt_count()); preempt_count() = prev_count; } - rcu_bh_qs(cpu); + if (need_rcu_bh_qs) + rcu_bh_qs(cpu); } local_irq_disable(); } @@ -331,7 +332,7 @@ restart: /* Reset the pending bitmask before enabling irqs */ set_softirq_pending(0); - handle_pending_softirqs(pending, cpu); + handle_pending_softirqs(pending, cpu, 1); pending = local_softirq_pending(); if (pending) { @@ -384,7 +385,12 @@ static void ksoftirqd_clr_sched_params(unsigned int cpu, bool online) { } static DEFINE_LOCAL_IRQ_LOCK(local_softirq_lock); static DEFINE_PER_CPU(struct task_struct *, local_softirq_runner); -static void __do_softirq(void); +static void __do_softirq_common(int need_rcu_bh_qs); + +void __do_softirq(void) +{ + __do_softirq_common(0); +} void __init softirq_early_init(void) { @@ -455,7 +461,7 @@ EXPORT_SYMBOL(in_serving_softirq); * Called with bh and local interrupts disabled. For full RT cpu must * be pinned. */ -static void __do_softirq(void) +static void __do_softirq_common(int need_rcu_bh_qs) { u32 pending = local_softirq_pending(); int cpu = smp_processor_id(); @@ -469,7 +475,7 @@ static void __do_softirq(void) lockdep_softirq_enter(); - handle_pending_softirqs(pending, cpu); + handle_pending_softirqs(pending, cpu, need_rcu_bh_qs); pending = local_softirq_pending(); if (pending) @@ -508,7 +514,7 @@ static int __thread_do_softirq(int cpu) * schedule! */ if (local_softirq_pending()) - __do_softirq(); + __do_softirq_common(cpu >= 0); local_unlock(local_softirq_lock); unpin_current_cpu(); preempt_disable(); |