Edit File: 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_ */