xref: /linux/kernel/unwind/deferred.c (revision b9c73524106e1c0c857006fb9ff2e5a510dc4021)

// SPDX-License-Identifier: GPL-2.0
/*
 * Deferred user space unwinding
 */
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/sizes.h>
#include <linux/slab.h>
#include <linux/unwind_deferred.h>

/* Make the cache fit in a 4K page */
#define UNWIND_MAX_ENTRIES					\
	((SZ_4K - sizeof(struct unwind_cache)) / sizeof(long))

/**
 * unwind_user_faultable - Produce a user stacktrace in faultable context
 * @trace: The descriptor that will store the user stacktrace
 *
 * This must be called in a known faultable context (usually when entering
 * or exiting user space). Depending on the available implementations
 * the @trace will be loaded with the addresses of the user space stacktrace
 * if it can be found.
 *
 * Return: 0 on success and negative on error
 *         On success @trace will contain the user space stacktrace
 */
int unwind_user_faultable(struct unwind_stacktrace *trace)
{
	struct unwind_task_info *info = &current->unwind_info;
	struct unwind_cache *cache;

	/* Should always be called from faultable context */
	might_fault();

	if (current->flags & PF_EXITING)
		return -EINVAL;

	if (!info->cache) {
		info->cache = kzalloc(struct_size(cache, entries, UNWIND_MAX_ENTRIES),
				      GFP_KERNEL);
		if (!info->cache)
			return -ENOMEM;
	}

	cache = info->cache;
	trace->entries = cache->entries;

	if (cache->nr_entries) {
		/*
		 * The user stack has already been previously unwound in this
		 * entry context.  Skip the unwind and use the cache.
		 */
		trace->nr = cache->nr_entries;
		return 0;
	}

	trace->nr = 0;
	unwind_user(trace, UNWIND_MAX_ENTRIES);

	cache->nr_entries = trace->nr;

	return 0;
}

void unwind_task_init(struct task_struct *task)
{
	struct unwind_task_info *info = &task->unwind_info;

	memset(info, 0, sizeof(*info));
}

void unwind_task_free(struct task_struct *task)
{
	struct unwind_task_info *info = &task->unwind_info;

	kfree(info->cache);
}