/* * Copyright (C) 2009 Matt Fleming * * Based, in part, on kernel/time/clocksource.c. * * This file provides arbitration code for stack unwinders. * * Multiple stack unwinders can be available on a system, usually with * the most accurate unwinder being the currently active one. */ #include #include #include #include #include /* * This is the most basic stack unwinder an architecture can * provide. For architectures without reliable frame pointers, e.g. * RISC CPUs, it can be implemented by looking through the stack for * addresses that lie within the kernel text section. * * Other CPUs, e.g. x86, can use their frame pointer register to * construct more accurate stack traces. */ static struct list_head unwinder_list; static struct unwinder stack_reader = { .name = "stack-reader", .dump = stack_reader_dump, .rating = 50, .list = { .next = &unwinder_list, .prev = &unwinder_list, }, }; /* * "curr_unwinder" points to the stack unwinder currently in use. This * is the unwinder with the highest rating. * * "unwinder_list" is a linked-list of all available unwinders, sorted * by rating. * * All modifications of "curr_unwinder" and "unwinder_list" must be * performed whilst holding "unwinder_lock". */ static struct unwinder *curr_unwinder = &stack_reader; static struct list_head unwinder_list = { .next = &stack_reader.list, .prev = &stack_reader.list, }; static DEFINE_SPINLOCK(unwinder_lock); static atomic_t unwinder_running = ATOMIC_INIT(0); /** * select_unwinder - Select the best registered stack unwinder. * * Private function. Must hold unwinder_lock when called. * * Select the stack unwinder with the best rating. This is useful for * setting up curr_unwinder. */ static struct unwinder *select_unwinder(void) { struct unwinder *best; if (list_empty(&unwinder_list)) return NULL; best = list_entry(unwinder_list.next, struct unwinder, list); if (best == curr_unwinder) return NULL; return best; } /* * Enqueue the stack unwinder sorted by rating. */ static int unwinder_enqueue(struct unwinder *ops) { struct list_head *tmp, *entry = &unwinder_list; list_for_each(tmp, &unwinder_list) { struct unwinder *o; o = list_entry(tmp, struct unwinder, list); if (o == ops) return -EBUSY; /* Keep track of the place, where to insert */ if (o->rating >= ops->rating) entry = tmp; } list_add(&ops->list, entry); return 0; } /** * unwinder_register - Used to install new stack unwinder * @u: unwinder to be registered * * Install the new stack unwinder on the unwinder list, which is sorted * by rating. * * Returns -EBUSY if registration fails, zero otherwise. */ int unwinder_register(struct unwinder *u) { unsigned long flags; int ret; spin_lock_irqsave(&unwinder_lock, flags); ret = unwinder_enqueue(u); if (!ret) curr_unwinder = select_unwinder(); spin_unlock_irqrestore(&unwinder_lock, flags); return ret; } /* * Unwind the call stack and pass information to the stacktrace_ops * functions. Also handle the case where we need to switch to a new * stack dumper because the current one faulted unexpectedly. */ void unwind_stack(struct task_struct *task, struct pt_regs *regs, unsigned long *sp, const struct stacktrace_ops *ops, void *data) { unsigned long flags; /* * The problem with unwinders with high ratings is that they are * inherently more complicated than the simple ones with lower * ratings. We are therefore more likely to fault in the * complicated ones, e.g. hitting BUG()s. If we fault in the * code for the current stack unwinder we try to downgrade to * one with a lower rating. * * Hopefully this will give us a semi-reliable stacktrace so we * can diagnose why curr_unwinder->dump() faulted. */ if (atomic_inc_return(&unwinder_running) != 1) { spin_lock_irqsave(&unwinder_lock, flags); if (!list_is_singular(&unwinder_list)) { list_del(&curr_unwinder->list); curr_unwinder = select_unwinder(); } spin_unlock_irqrestore(&unwinder_lock, flags); atomic_dec(&unwinder_running); } curr_unwinder->dump(task, regs, sp, ops, data); atomic_dec(&unwinder_running); }