| Subject: rcu: Make ksoftirqd do RCU quiescent states |
| From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> |
| Date: Wed, 5 Oct 2011 11:45:18 -0700 |
| |
| 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> |
| |
| --- |
| include/linux/rcupdate.h | 4 ---- |
| kernel/rcu/tree.c | 9 ++++++++- |
| kernel/rcu/tree_plugin.h | 8 +++++++- |
| 3 files changed, 15 insertions(+), 6 deletions(-) |
| |
| --- a/include/linux/rcupdate.h |
| +++ b/include/linux/rcupdate.h |
| @@ -303,11 +303,7 @@ static inline int rcu_preempt_depth(void |
| /* Internal to kernel */ |
| void rcu_init(void); |
| void rcu_sched_qs(void); |
| -#ifdef CONFIG_PREEMPT_RT_FULL |
| -static inline void rcu_bh_qs(void) { } |
| -#else |
| void rcu_bh_qs(void); |
| -#endif |
| void rcu_check_callbacks(int user); |
| void rcu_report_dead(unsigned int cpu); |
| void rcu_cpu_starting(unsigned int cpu); |
| --- a/kernel/rcu/tree.c |
| +++ b/kernel/rcu/tree.c |
| @@ -262,7 +262,14 @@ void rcu_sched_qs(void) |
| this_cpu_ptr(&rcu_sched_data), true); |
| } |
| |
| -#ifndef CONFIG_PREEMPT_RT_FULL |
| +#ifdef CONFIG_PREEMPT_RT_FULL |
| +static void rcu_preempt_qs(void); |
| + |
| +void rcu_bh_qs(void) |
| +{ |
| + rcu_preempt_qs(); |
| +} |
| +#else |
| void rcu_bh_qs(void) |
| { |
| if (__this_cpu_read(rcu_bh_data.cpu_no_qs.s)) { |
| --- a/kernel/rcu/tree_plugin.h |
| +++ b/kernel/rcu/tree_plugin.h |
| @@ -29,6 +29,7 @@ |
| #include <linux/oom.h> |
| #include <linux/sched/debug.h> |
| #include <linux/smpboot.h> |
| +#include <linux/jiffies.h> |
| #include <uapi/linux/sched/types.h> |
| #include "../time/tick-internal.h" |
| |
| @@ -1246,7 +1247,7 @@ static void rcu_prepare_kthreads(int cpu |
| |
| #endif /* #else #ifdef CONFIG_RCU_BOOST */ |
| |
| -#if !defined(CONFIG_RCU_FAST_NO_HZ) |
| +#if !defined(CONFIG_RCU_FAST_NO_HZ) || defined(CONFIG_PREEMPT_RT_FULL) |
| |
| /* |
| * Check to see if any future RCU-related work will need to be done |
| @@ -1263,7 +1264,9 @@ int rcu_needs_cpu(u64 basemono, u64 *nex |
| return IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL) |
| ? 0 : rcu_cpu_has_callbacks(NULL); |
| } |
| +#endif /* !defined(CONFIG_RCU_FAST_NO_HZ) || defined(CONFIG_PREEMPT_RT_FULL) */ |
| |
| +#if !defined(CONFIG_RCU_FAST_NO_HZ) |
| /* |
| * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up |
| * after it. |
| @@ -1359,6 +1362,8 @@ static bool __maybe_unused rcu_try_advan |
| return cbs_ready; |
| } |
| |
| +#ifndef CONFIG_PREEMPT_RT_FULL |
| + |
| /* |
| * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready |
| * to invoke. If the CPU has callbacks, try to advance them. Tell the |
| @@ -1404,6 +1409,7 @@ int rcu_needs_cpu(u64 basemono, u64 *nex |
| *nextevt = basemono + dj * TICK_NSEC; |
| return 0; |
| } |
| +#endif /* #ifndef CONFIG_PREEMPT_RT_FULL */ |
| |
| /* |
| * Prepare a CPU for idle from an RCU perspective. The first major task |