Re: [PATCH 2/9] liblockdep: Wrap kernel/lockdep.c to allow usagefrom userspace

From: Peter Zijlstra
Date: Wed May 08 2013 - 06:03:39 EST


On Tue, Apr 30, 2013 at 02:54:33PM -0400, Sasha Levin wrote:
> diff --git a/tools/lib/lockdep/common.c b/tools/lib/lockdep/common.c
> new file mode 100644
> index 0000000..eb5e481
> --- /dev/null
> +++ b/tools/lib/lockdep/common.c
> @@ -0,0 +1,33 @@
> +#include <stddef.h>
> +#include <stdbool.h>
> +#include <linux/compiler.h>
> +#include <linux/lockdep.h>
> +#include <unistd.h>
> +#include <sys/syscall.h>
> +
> +static struct task_struct current_obj;
> +
> +/* lockdep wants these */
> +bool debug_locks = true;
> +bool debug_locks_silent;
> +
> +__attribute__((constructor)) static void liblockdep_init(void)
> +{
> + lockdep_init();
> +}
> +
> +__attribute__((destructor)) static void liblockdep_exit(void)
> +{
> + debug_check_no_locks_held(&current_obj);
> +}
> +
> +struct task_struct *__curr(void)
> +{
> + if (current_obj.pid == 0) {
> + /* Makes lockdep output pretty */
> + prctl(PR_GET_NAME, current_obj.comm);
> + current_obj.pid = syscall(__NR_gettid);
> + }
> +
> + return &current_obj;
> +}

> diff --git a/tools/lib/lockdep/uinclude/linux/lockdep.h b/tools/lib/lockdep/uinclude/linux/lockdep.h
> new file mode 100644
> index 0000000..8e9a5c4
> --- /dev/null
> +++ b/tools/lib/lockdep/uinclude/linux/lockdep.h
> @@ -0,0 +1,58 @@
> +#ifndef _LIBLOCKDEP_LOCKDEP_H_
> +#define _LIBLOCKDEP_LOCKDEP_H_
> +
> +#include <sys/prctl.h>
> +#include <sys/syscall.h>
> +#include <string.h>
> +#include <limits.h>
> +#include <linux/utsname.h>
> +
> +
> +#define MAX_LOCK_DEPTH 2000UL
> +
> +#include "../../../include/linux/lockdep.h"
> +
> +struct task_struct {
> + u64 curr_chain_key;
> + int lockdep_depth;
> + unsigned int lockdep_recursion;
> + struct held_lock held_locks[MAX_LOCK_DEPTH];
> + gfp_t lockdep_reclaim_gfp;
> + int pid;
> + char comm[17];
> +};
> +
> +extern struct task_struct *__curr(void);
> +
> +#define current (__curr())
> +
> +#define debug_locks_off() 1
> +#define task_pid_nr(tsk) ((tsk)->pid)
> +
> +#define KSYM_NAME_LEN 128
> +#define printk printf
> +
> +#define KERN_ERR
> +#define KERN_CONT
> +
> +#define list_del_rcu list_del
> +
> +#define atomic_t unsigned long
> +#define atomic_inc(x) ((*(x))++)
> +
> +static struct new_utsname *init_utsname(void)
> +{
> + static struct new_utsname n = (struct new_utsname) {
> + .release = "liblockdep",
> + .version = LIBLOCKDEP_VERSION,
> + };
> +
> + return &n;
> +}
> +
> +#define print_tainted() ""
> +#define static_obj(x) 1
> +
> +#define debug_show_all_locks()
> +
> +#endif

I don't see how this could possible work for threaded programs; you only have a
single task_struct instance. Wouldn't you need something like the below?

---

static int (*pthread_create_orig)(pthread_t *__restrict,
__const pthread_attr_t *__restrict,
void *(*)(void *),
void *__restrict) = NULL;


static __thread struct task_struct __current;

#define current (&__current)

static void sched_fork(void)
{
/* init __current */
}

__attribute__((constructor)) static void sched_init(void)
{
pthread_create_orig = dlsym(RTLD_NEXT, "pthread_create");
if (!pthread_create_orig) {
char *error = dlerror();
if (!error)
error = "pthread_create is NULL";
die("%s\n", error);
}

sched_fork(); /* main thread */
}

__attribute__((destructor)) static void sched_exit(void)
{
/* */
}

struct tramp_data {

void *(*func)(void *);
void *arg;

pthread_mutex_t lock;
pthread_cond_t wait;
};

static void *tramp_func(void *data)
{
struct tramp_data *tramp_data = data;
void *(*func)(void *) = tramp_data->func;
void *arg = tramp_data->arg;

sched_fork();

pthread_mutex_lock(&tramp_data->lock);
pthread_cond_signal(&tramp_data->wait);
pthread_mutex_unlock(&tramp_data->lock);

return func(arg);
}

/* hijack pthread_create() */
int pthread_create(pthread_t *__restrict thread,
__const pthread_attr_t *__restrict attr,
void *(*func)(void *),
void *__restrict arg)
{
struct tramp_data tramp_data = {
.func = func,
.arg = arg,
};
int ret;

pthread_cond_init(&tramp_data.wait, NULL);
pthread_mutex_init(&tramp_data.lock, NULL);

pthread_mutex_lock(&tramp_data.lock);

ret = pthread_create_orig(thread, attr, &tramp_func, &tramp_data);
if (!ret)
pthread_cond_wait(&tramp_data.wait, &tramp_data.lock);

pthread_mutex_unlock(&tramp_data.lock);

pthread_mutex_destroy(&tramp_data.lock);
pthread_cond_destroy(&tramp_data.wait);

return ret;
}

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/