Current File : //usr/share/systemtap/runtime/linux/runtime_context.h
/* -*- linux-c -*-
* Context Runtime Functions
* Copyright (C) 2014 Red Hat Inc.
*
* This file is part of systemtap, and is free software. You can
* redistribute it and/or modify it under the terms of the GNU General
* Public License (GPL); either version 2, or (at your option) any
* later version.
*/
#ifndef _LINUX_RUNTIME_CONTEXT_H_
#define _LINUX_RUNTIME_CONTEXT_H_
#ifndef __rcu
#define __rcu
#endif
static struct context __rcu *contexts[NR_CPUS] = { NULL };
static int _stp_runtime_contexts_alloc(void)
{
int cpu;
for_each_possible_cpu(cpu) {
/* Module init, so in user context, safe to use
* "sleeping" allocation. */
struct context *c = _stp_vzalloc_node(sizeof (struct context),
cpu_to_node(cpu));
if (c == NULL) {
_stp_error ("context (size %lu per cpu) allocation failed",
(unsigned long) sizeof (struct context));
return -ENOMEM;
}
rcu_assign_pointer(contexts[cpu], c);
}
return 0;
}
/* We should be free of all probes by this time, but for example the timer for
* _stp_ctl_work_callback may still be running and looking for contexts. We
* use RCU-sched synchronization to be sure its safe to free them. */
static void _stp_runtime_contexts_free(void)
{
// Note that 'free_contexts' is static because it is
// (probably) too big to fit on a kernel function's stack.
static struct context *free_contexts[NR_CPUS] = { NULL };
int cpu;
/* First, save all the pointers. */
rcu_read_lock_sched();
for_each_possible_cpu(cpu) {
free_contexts[cpu] = rcu_dereference_sched(contexts[cpu]);
}
rcu_read_unlock_sched();
/* Now clear all pointers to prevent new readers. */
for_each_possible_cpu(cpu) {
rcu_assign_pointer(contexts[cpu], NULL);
}
/* Sync to make sure existing readers are done. */
stp_synchronize_sched();
/* Now we can actually free the contexts. */
for_each_possible_cpu(cpu) {
struct context *c = free_contexts[cpu];
if (c != NULL) {
free_contexts[cpu] = NULL;
_stp_vfree(c);
}
}
}
static inline struct context * _stp_runtime_get_context(void)
{
return rcu_dereference_sched(contexts[smp_processor_id()]);
}
static struct context * _stp_runtime_entryfn_get_context(void)
{
struct context* __restrict__ c = NULL;
preempt_disable ();
c = _stp_runtime_get_context();
if (c != NULL) {
if (atomic_inc_return(&c->busy) == 1) {
// NB: Notice we're not re-enabling preemption
// here. We exepect the calling code to call
// _stp_runtime_entryfn_get_context() and
// _stp_runtime_entryfn_put_context() as a
// pair.
return c;
}
atomic_dec(&c->busy);
}
preempt_enable_no_resched();
return NULL;
}
static inline void _stp_runtime_entryfn_put_context(struct context *c)
{
if (c) {
if (c == _stp_runtime_get_context())
atomic_dec(&c->busy);
/* else, warn about bad state? */
preempt_enable_no_resched();
}
return;
}
static void _stp_runtime_context_wait(void)
{
int holdon;
unsigned long hold_start;
int hold_index;
hold_start = jiffies;
hold_index = -1;
do {
int i;
holdon = 0;
rcu_read_lock_sched();
for_each_possible_cpu(i) {
struct context *c = rcu_dereference_sched(contexts[i]);
if (c != NULL
&& atomic_read (& c->busy)) {
holdon = 1;
/* Just in case things are really
* stuck, let's print some diagnostics. */
if (time_after(jiffies, hold_start + HZ) // > 1 second
&& (i > hold_index)) { // not already printed
hold_index = i;
printk(KERN_ERR "%s context[%d] stuck: %s\n", THIS_MODULE->name, i, c->probe_point);
}
}
}
rcu_read_unlock_sched();
/*
* Just in case things are really really stuck, a
* handler probably suffered a fault, and the kernel
* probably killed a task/thread already. We can't be
* quite sure in what state everything is in, however
* auxiliary stuff like kprobes / uprobes / locks have
* already been unregistered. So it's *probably* safe
* to pretend/assume/hope everything is OK, and let
* the cleanup finish.
*
* In the worst case, there may occur a fault, as a
* genuinely running probe handler tries to access
* script globals (about to be freed), or something
* accesses module memory (about to be unloaded).
* This is sometimes stinky, so the alternative
* (default) is to change from a livelock to a
* livelock that sleeps awhile.
*/
#ifdef STAP_OVERRIDE_STUCK_CONTEXT
if (time_after(jiffies, hold_start + HZ*10)) { // > 10 seconds
printk(KERN_ERR "%s overriding stuck context to allow module shutdown.", THIS_MODULE->name);
holdon = 0; // allow loop to exit
}
#else
/* at least stop sucking down the staprun cpu */
msleep(250);
#endif
/* NB: we run at least one of these during the
* shutdown sequence: */
yield(); /* aka schedule() and then some */
} while (holdon);
}
#endif /* _LINUX_RUNTIME_CONTEXT_H_ */
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