Commit 43a89bae authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Daniel Borkmann
Browse files

rcu: Export rcu_request_urgent_qs_task() 



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: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20230706033447.54696-11-alexei.starovoitov@gmail.com
parent 04fabf00

include/linux/rcutiny.h

+2 −0
Original line number Diff line number Diff line
@@ -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.

include/linux/rcutree.h

+1 −0
Original line number Diff line number Diff line
@@ -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

kernel/rcu/rcu.h

+0 −2
Original line number Diff line number Diff line
@@ -493,7 +493,6 @@ static inline void rcu_expedite_gp(void) { } 
static inline void rcu_unexpedite_gp(void) { }

static inline void rcu_async_hurry(void) { }

static inline void rcu_async_relax(void) { }

static inline void rcu_request_urgent_qs_task(struct task_struct *t) { }

#else /* #ifdef CONFIG_TINY_RCU */

bool rcu_gp_is_normal(void);     /* Internal RCU use. */

bool rcu_gp_is_expedited(void);  /* Internal RCU use. */
@@ -508,7 +507,6 @@ 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