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Date: Wed, 08 May 2013 09:27:46 -0400
From: Sasha Levin <sasha.levin@...cle.com>
To: Peter Zijlstra <peterz@...radead.org>
CC: torvalds@...ux-foundation.org, mingo@...nel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/9] liblockdep: Wrap kernel/lockdep.c to allow usage
from userspace
On 05/08/2013 06:01 AM, Peter Zijlstra wrote:
> 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(¤t_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 ¤t_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?
[snip]
Hi Peter,
You're right - I broke multithreading for some odd reason (mostly me being stupid)
after having it working :/
It's enough to set the __thread flag on current_obj:
diff --git a/tools/lib/lockdep/common.c b/tools/lib/lockdep/common.c
index eb5e481..8ef602f 100644
--- a/tools/lib/lockdep/common.c
+++ b/tools/lib/lockdep/common.c
@@ -5,7 +5,7 @@
#include <unistd.h>
#include <sys/syscall.h>
-static struct task_struct current_obj;
+static __thread struct task_struct current_obj;
/* lockdep wants these */
bool debug_locks = true;
Since we don't need any special initialization of the struct at any point. This
means that the patch above is enough and we don't need to hook pthread_create.
I've tested it by adding the following test to the tests dir:
#include <pthread.h>
#include <liblockdep/mutex.h>
#include "common.h"
pthread_mutex_t a, b;
static void *thread_a(void *arg)
{
LOCK_UNLOCK_2(a, b);
return NULL;
}
static void *thread_b(void *arg)
{
LOCK_UNLOCK_2(b, a);
return NULL;
}
void main(void)
{
pthread_t ta, tb;
pthread_mutex_init(&a, NULL);
pthread_mutex_init(&b, NULL);
pthread_create(&ta, NULL, thread_a, NULL);
pthread_create(&tb, NULL, thread_b, NULL);
pthread_join(ta, NULL);
pthread_join(tb, NULL);
}
Which, as expected, produced the following spew:
======================================================
[ INFO: possible circular locking dependency detected ]
liblockdep 0.0.1
-------------------------------------------------------
ABBA_MT/30105 is trying to acquire lock:
(&a){......}, at: /lib64/libpthread.so.0(+0x8f3b) [0x7ffa7d2f1f3b]
but task is already holding lock:
(&b){......}, at: /lib64/libpthread.so.0(+0x8f3b) [0x7ffa7d2f1f3b]
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&b){......}:
tests/ABBA_MT[0x4017e4]
tests/ABBA_MT[0x403381]
tests/ABBA_MT[0x40361b]
tests/ABBA_MT[0x403cb1]
tests/ABBA_MT[0x40476e]
tests/ABBA_MT[0x40522d]
tests/ABBA_MT[0x4012d2]
/lib64/libpthread.so.0(+0x8f3b)[0x7ffa7d2f1f3b]
/lib64/libc.so.6(clone+0x6d)[0x7ffa7d02d26d]
-> #0 (&a){......}:
tests/ABBA_MT[0x4017e4]
tests/ABBA_MT[0x402c95]
tests/ABBA_MT[0x403267]
tests/ABBA_MT[0x40361b]
tests/ABBA_MT[0x403cb1]
tests/ABBA_MT[0x40476e]
tests/ABBA_MT[0x40522d]
tests/ABBA_MT[0x401372]
/lib64/libpthread.so.0(+0x8f3b)[0x7ffa7d2f1f3b]
/lib64/libc.so.6(clone+0x6d)[0x7ffa7d02d26d]
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&b);
lock(&a);
lock(&b);
lock(&a);
*** DEADLOCK ***
1 lock held by ABBA_MT/30105:
#0: (&b){......}, at: /lib64/libpthread.so.0(+0x8f3b) [0x7ffa7d2f1f3b]
stack backtrace:
tests/ABBA_MT[0x401518]
tests/ABBA_MT[0x402d4f]
tests/ABBA_MT[0x403267]
tests/ABBA_MT[0x40361b]
tests/ABBA_MT[0x403cb1]
tests/ABBA_MT[0x40476e]
tests/ABBA_MT[0x40522d]
tests/ABBA_MT[0x401372]
/lib64/libpthread.so.0(+0x8f3b)[0x7ffa7d2f1f3b]
/lib64/libc.so.6(clone+0x6d)[0x7ffa7d02d26d]
Thanks,
Sasha
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