165 lines
4.2 KiB
C
165 lines
4.2 KiB
C
/*
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* Copyright (C) 2009 Matt Fleming
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*
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* Based, in part, on kernel/time/clocksource.c.
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*
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* This file provides arbitration code for stack unwinders.
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*
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* Multiple stack unwinders can be available on a system, usually with
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* the most accurate unwinder being the currently active one.
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*/
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#include <linux/errno.h>
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#include <linux/list.h>
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#include <linux/spinlock.h>
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#include <linux/module.h>
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#include <asm/unwinder.h>
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#include <linux/atomic.h>
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/*
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* This is the most basic stack unwinder an architecture can
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* provide. For architectures without reliable frame pointers, e.g.
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* RISC CPUs, it can be implemented by looking through the stack for
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* addresses that lie within the kernel text section.
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*
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* Other CPUs, e.g. x86, can use their frame pointer register to
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* construct more accurate stack traces.
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*/
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static struct list_head unwinder_list;
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static struct unwinder stack_reader = {
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.name = "stack-reader",
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.dump = stack_reader_dump,
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.rating = 50,
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.list = {
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.next = &unwinder_list,
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.prev = &unwinder_list,
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},
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};
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/*
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* "curr_unwinder" points to the stack unwinder currently in use. This
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* is the unwinder with the highest rating.
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*
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* "unwinder_list" is a linked-list of all available unwinders, sorted
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* by rating.
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*
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* All modifications of "curr_unwinder" and "unwinder_list" must be
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* performed whilst holding "unwinder_lock".
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*/
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static struct unwinder *curr_unwinder = &stack_reader;
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static struct list_head unwinder_list = {
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.next = &stack_reader.list,
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.prev = &stack_reader.list,
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};
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static DEFINE_SPINLOCK(unwinder_lock);
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/**
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* select_unwinder - Select the best registered stack unwinder.
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*
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* Private function. Must hold unwinder_lock when called.
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*
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* Select the stack unwinder with the best rating. This is useful for
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* setting up curr_unwinder.
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*/
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static struct unwinder *select_unwinder(void)
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{
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struct unwinder *best;
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if (list_empty(&unwinder_list))
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return NULL;
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best = list_entry(unwinder_list.next, struct unwinder, list);
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if (best == curr_unwinder)
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return NULL;
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return best;
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}
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/*
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* Enqueue the stack unwinder sorted by rating.
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*/
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static int unwinder_enqueue(struct unwinder *ops)
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{
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struct list_head *tmp, *entry = &unwinder_list;
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list_for_each(tmp, &unwinder_list) {
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struct unwinder *o;
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o = list_entry(tmp, struct unwinder, list);
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if (o == ops)
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return -EBUSY;
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/* Keep track of the place, where to insert */
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if (o->rating >= ops->rating)
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entry = tmp;
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}
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list_add(&ops->list, entry);
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return 0;
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}
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/**
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* unwinder_register - Used to install new stack unwinder
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* @u: unwinder to be registered
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*
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* Install the new stack unwinder on the unwinder list, which is sorted
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* by rating.
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*
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* Returns -EBUSY if registration fails, zero otherwise.
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*/
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int unwinder_register(struct unwinder *u)
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{
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unsigned long flags;
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int ret;
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spin_lock_irqsave(&unwinder_lock, flags);
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ret = unwinder_enqueue(u);
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if (!ret)
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curr_unwinder = select_unwinder();
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spin_unlock_irqrestore(&unwinder_lock, flags);
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return ret;
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}
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int unwinder_faulted = 0;
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/*
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* Unwind the call stack and pass information to the stacktrace_ops
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* functions. Also handle the case where we need to switch to a new
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* stack dumper because the current one faulted unexpectedly.
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*/
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void unwind_stack(struct task_struct *task, struct pt_regs *regs,
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unsigned long *sp, const struct stacktrace_ops *ops,
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void *data)
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{
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unsigned long flags;
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/*
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* The problem with unwinders with high ratings is that they are
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* inherently more complicated than the simple ones with lower
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* ratings. We are therefore more likely to fault in the
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* complicated ones, e.g. hitting BUG()s. If we fault in the
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* code for the current stack unwinder we try to downgrade to
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* one with a lower rating.
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*
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* Hopefully this will give us a semi-reliable stacktrace so we
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* can diagnose why curr_unwinder->dump() faulted.
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*/
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if (unwinder_faulted) {
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spin_lock_irqsave(&unwinder_lock, flags);
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/* Make sure no one beat us to changing the unwinder */
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if (unwinder_faulted && !list_is_singular(&unwinder_list)) {
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list_del(&curr_unwinder->list);
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curr_unwinder = select_unwinder();
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unwinder_faulted = 0;
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}
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spin_unlock_irqrestore(&unwinder_lock, flags);
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}
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curr_unwinder->dump(task, regs, sp, ops, data);
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}
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EXPORT_SYMBOL_GPL(unwind_stack);
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