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Date: Fri, 10 May 2013 15:11:20 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Sasha Levin <sasha.levin@...cle.com>
Cc: torvalds@...ux-foundation.org, mingo@...nel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 7/9] liblockdep: Support using LD_PRELOAD
On Fri, May 10, 2013 at 01:46:05PM +0200, Peter Zijlstra wrote:
> OK, that won't do indeed. Not being able to malloc is only part of the problem.
>
> /me goes stare at it more
So the below hackery actually does run with firefox -- although it generates a
metric ton of output.
It very much relies on the gnu-libc (although it should work with both the NPTL
and LinuxThread implementations).
The static allocation stuff is still there but shouldn't be needed for this.
---
--- a/tools/lib/lockdep/Makefile
+++ b/tools/lib/lockdep/Makefile
@@ -146,7 +146,7 @@ do_app_build = \
do_compile_shared_library = \
($(print_shared_lib_compile) \
- $(CC) --shared -ldl $^ -o $@)
+ $(CC) --shared $^ -o $@ -lpthread -ldl)
do_build_static_lib = \
($(print_static_lib_build) \
--- a/tools/lib/lockdep/preload.c
+++ b/tools/lib/lockdep/preload.c
@@ -1,4 +1,5 @@
#define _GNU_SOURCE
+#include <sysexits.h>
#include <pthread.h>
#include <stdio.h>
#include <dlfcn.h>
@@ -29,28 +30,63 @@ static struct rb_root locks = RB_ROOT;
static pthread_rwlock_t locks_rwlock = PTHREAD_RWLOCK_INITIALIZER;
/* pthread mutex API */
+
+#ifdef __GLIBC__
+extern int __pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutexattr_t *attr);
+extern int __pthread_mutex_lock(pthread_mutex_t *mutex);
+extern int __pthread_mutex_trylock(pthread_mutex_t *mutex);
+extern int __pthread_mutex_unlock(pthread_mutex_t *mutex);
+extern int __pthread_mutex_destroy(pthread_mutex_t *mutex);
+#else
+#define __pthread_mutex_init NULL
+#define __pthread_mutex_lock NULL
+#define __pthread_mutex_trylock NULL
+#define __pthread_mutex_unlock NULL
+#define __pthread_mutex_destroy NULL
+#endif
+
static int (*ll_pthread_mutex_init)(pthread_mutex_t *mutex,
- const pthread_mutexattr_t *attr);
-static int (*ll_pthread_mutex_lock)(pthread_mutex_t *mutex);
-static int (*ll_pthread_mutex_trylock)(pthread_mutex_t *mutex);
-static int (*ll_pthread_mutex_unlock)(pthread_mutex_t *mutex);
-static int (*ll_pthread_mutex_destroy)(pthread_mutex_t *mutex);
+ const pthread_mutexattr_t *attr) = __pthread_mutex_init;
+static int (*ll_pthread_mutex_lock)(pthread_mutex_t *mutex) = __pthread_mutex_lock;
+static int (*ll_pthread_mutex_trylock)(pthread_mutex_t *mutex) = __pthread_mutex_trylock;
+static int (*ll_pthread_mutex_unlock)(pthread_mutex_t *mutex) = __pthread_mutex_unlock;
+static int (*ll_pthread_mutex_destroy)(pthread_mutex_t *mutex) = __pthread_mutex_destroy;
/* pthread rwlock API */
+
+#ifdef __GLIBC__
+extern int __pthread_rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr);
+extern int __pthread_rwlock_destroy(pthread_rwlock_t *rwlock);
+extern int __pthread_rwlock_wrlock(pthread_rwlock_t *rwlock);
+extern int __pthread_rwlock_trywrlock(pthread_rwlock_t *rwlock);
+extern int __pthread_rwlock_rdlock(pthread_rwlock_t *rwlock);
+extern int __pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock);
+extern int __pthread_rwlock_unlock(pthread_rwlock_t *rwlock);
+#else
+#define __pthread_rwlock_init NULL
+#define __pthread_rwlock_destroy NULL
+#define __pthread_rwlock_wrlock NULL
+#define __pthread_rwlock_trywrlock NULL
+#define __pthread_rwlock_rdlock NULL
+#define __pthread_rwlock_tryrdlock NULL
+#define __pthread_rwlock_unlock NULL
+#endif
+
static int (*ll_pthread_rwlock_init)(pthread_rwlock_t *rwlock,
- const pthread_rwlockattr_t *attr);
-static int (*ll_pthread_rwlock_destroy)(pthread_rwlock_t *rwlock);
-static int (*ll_pthread_rwlock_rdlock)(pthread_rwlock_t *rwlock);
-static int (*ll_pthread_rwlock_tryrdlock)(pthread_rwlock_t *rwlock);
-static int (*ll_pthread_rwlock_trywrlock)(pthread_rwlock_t *rwlock);
-static int (*ll_pthread_rwlock_wrlock)(pthread_rwlock_t *rwlock);
-static int (*ll_pthread_rwlock_unlock)(pthread_rwlock_t *rwlock);
+ const pthread_rwlockattr_t *attr) = __pthread_rwlock_init;
+static int (*ll_pthread_rwlock_destroy)(pthread_rwlock_t *rwlock) = __pthread_rwlock_destroy;
+static int (*ll_pthread_rwlock_rdlock)(pthread_rwlock_t *rwlock) = __pthread_rwlock_rdlock;
+static int (*ll_pthread_rwlock_tryrdlock)(pthread_rwlock_t *rwlock) = __pthread_rwlock_tryrdlock;
+static int (*ll_pthread_rwlock_trywrlock)(pthread_rwlock_t *rwlock) = __pthread_rwlock_trywrlock;
+static int (*ll_pthread_rwlock_wrlock)(pthread_rwlock_t *rwlock) = __pthread_rwlock_wrlock;
+static int (*ll_pthread_rwlock_unlock)(pthread_rwlock_t *rwlock) = __pthread_rwlock_unlock;
+
+enum { none, prepare, done, } __init_state;
-static bool preload_done;
static void init_preload(void);
static void try_init_preload(void)
{
- if (!preload_done)
+ if (__init_state != done)
init_preload();
}
@@ -76,6 +112,56 @@ static struct rb_node **__get_lock_node(
return node;
}
+#ifndef LIBLOCKDEP_STATIC_ENTRIES
+#define LIBLOCKDEP_STATIC_ENTRIES 1024
+#endif
+
+#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
+
+static struct lock_lookup __locks[LIBLOCKDEP_STATIC_ENTRIES];
+static int __locks_nr;
+
+static inline bool is_static_lock(struct lock_lookup *lock)
+{
+ return lock >= __locks && lock < __locks + ARRAY_SIZE(__locks);
+}
+
+static struct lock_lookup *alloc_lock(void)
+{
+ if (__init_state != done) {
+ /*
+ * Some programs attempt to initialize and use locks in their
+ * allocation path. This means that a call to malloc() would
+ * result in locks being initialized and locked.
+ *
+ * Why is it an issue for us? dlsym() below will try allocating
+ * to give us the original function. Since this allocation will
+ * result in a locking operations, we have to let pthread deal
+ * with it, but we can't! we don't have the pointer to the
+ * original API since we're inside dlsym() trying to get it :(
+ */
+
+ /* XXX: can we be concurrent already? if so add lock */
+
+ int idx = __locks_nr++;
+ if (idx >= ARRAY_SIZE(__locks)) {
+ fprintf(stderr,
+ "LOCKDEP error: insufficient LIBLOCKDEP_STATIC_ENTRIES\n");
+
+ exit(EX_UNAVAILABLE);
+ }
+ return __locks + idx;
+ }
+
+ return malloc(sizeof(struct lock_lookup));
+}
+
+static inline void free_lock(struct lock_lookup *lock)
+{
+ if (likely(!is_static_lock(lock)))
+ free(lock);
+}
+
/**
* __get_lock - find or create a lock instance
* @lock: pointer to a pthread lock function
@@ -96,7 +182,7 @@ static struct lock_lookup *__get_lock(vo
}
/* We didn't find the lock, let's create it */
- l = malloc(sizeof(*l));
+ l = alloc_lock();
if (l == NULL)
return NULL;
@@ -125,7 +211,7 @@ static void __del_lock(struct lock_looku
ll_pthread_rwlock_wrlock(&locks_rwlock);
rb_erase(&lock->node, &locks);
ll_pthread_rwlock_unlock(&locks_rwlock);
- free(lock);
+ free_lock(lock);
}
int pthread_mutex_init(pthread_mutex_t *mutex,
@@ -329,40 +415,11 @@ int pthread_rwlock_unlock(pthread_rwlock
__attribute__((constructor)) static void init_preload(void)
{
- static bool preload_started;
-
- if (preload_done)
+ if (__init_state != done)
return;
- /*
- * Some programs attempt to initialize and use locks in their
- * allocation path. This means that a call to malloc() would
- * result in locks being initialized and locked.
- *
- * Why is it an issue for us? dlsym() below will try allocating to
- * give us the original function. Since this allocation will result
- * in a locking operations, we have to let pthread deal with it,
- * but we can't! we don't have the pointer to the original API
- * since we're inside dlsym() trying to get it :(
- *
- * We can work around it by telling the program that locking was
- * really okay, and just initialize those locks when we're fully
- * up and running (this is ok because this all happens during
- * initialization phase, when we have just one thread). But
- * this is a big TODO at this point.
- */
- if (preload_started) {
- printf(
- "LOCKDEP error: It seems that the program you are trying to "
- "debug is initializing locks in it's allocation path.\n"
- "This means that liblockdep cannot reliably analyze this "
- "program since we need the allocator to work before we can "
- "debug locks.\nSorry!\n");
-
- exit(1);
- }
-
- preload_started = true;
+#ifndef __GLIBC__
+ __init_state = prepare;
ll_pthread_mutex_init = dlsym(RTLD_NEXT, "pthread_mutex_init");
ll_pthread_mutex_lock = dlsym(RTLD_NEXT, "pthread_mutex_lock");
@@ -377,8 +434,9 @@ __attribute__((constructor)) static void
ll_pthread_rwlock_wrlock = dlsym(RTLD_NEXT, "pthread_rwlock_wrlock");
ll_pthread_rwlock_trywrlock = dlsym(RTLD_NEXT, "pthread_rwlock_trywrlock");
ll_pthread_rwlock_unlock = dlsym(RTLD_NEXT, "pthread_rwlock_unlock");
+#endif
lockdep_init();
- preload_done = true;
+ __init_state = done;
}
--
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