From: "Paul E. McKenney" paulmck@kernel.org
commit 43a89baecfe200cb4530f42b9fcf904925d6d14a upstream.
If a CPU is executing a long series of non-sleeping system calls, RCU grace periods can be delayed for on the order of a couple hundred milliseconds. This is normally not a problem, but if each system call does a call_rcu(), those callbacks can stack up. RCU will eventually notice this callback storm, but use of rcu_request_urgent_qs_task() allows the code invoking call_rcu() to give RCU a heads up.
This function is not for general use, not yet, anyway.
Reported-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net Link: https://lore.kernel.org/bpf/20230706033447.54696-11-alexei.starovoitov@gmail... Signed-off-by: Alexey Nepomnyashih sdl@nppct.ru --- include/linux/rcutiny.h | 2 ++ include/linux/rcutree.h | 1 + kernel/rcu/rcu.h | 4 ++-- 3 files changed, 5 insertions(+), 2 deletions(-)
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 768196a5f39d..68ebe147e45d 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -138,6 +138,8 @@ static inline int rcu_needs_cpu(void) return 0; }
+static inline void rcu_request_urgent_qs_task(struct task_struct *t) { } + /* * Take advantage of the fact that there is only one CPU, which * allows us to ignore virtualization-based context switches. diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index 5efb51486e8a..8d0cecced199 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -21,6 +21,7 @@ void rcu_softirq_qs(void); void rcu_note_context_switch(bool preempt); int rcu_needs_cpu(void); void rcu_cpu_stall_reset(void); +void rcu_request_urgent_qs_task(struct task_struct *t);
/* * Note a virtualization-based context switch. This is simply a diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index af6a06b86298..edff841a1a69 100644 --- a/kernel/rcu/rcu.h +++ b/kernel/rcu/rcu.h @@ -452,7 +452,8 @@ static inline bool rcu_gp_is_normal(void) { return true; } static inline bool rcu_gp_is_expedited(void) { return false; } static inline void rcu_expedite_gp(void) { } static inline void rcu_unexpedite_gp(void) { } -static inline void rcu_request_urgent_qs_task(struct task_struct *t) { } +static inline void rcu_async_hurry(void) { } +static inline void rcu_async_relax(void) { } #else /* #ifdef CONFIG_TINY_RCU */ bool rcu_gp_is_normal(void); /* Internal RCU use. */ bool rcu_gp_is_expedited(void); /* Internal RCU use. */ @@ -464,7 +465,6 @@ void show_rcu_tasks_gp_kthreads(void); #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ static inline void show_rcu_tasks_gp_kthreads(void) {} #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */ -void rcu_request_urgent_qs_task(struct task_struct *t); #endif /* #else #ifdef CONFIG_TINY_RCU */
#define RCU_SCHEDULER_INACTIVE 0