Re: [Xen-devel] [PATCH] Fix libxenstore memory leak when USE_PTHREAD is not defined

[Andres Lagar-Cavilla <andreslc@xxxxxxxxxxxxxx>]

On Sep 14, 2012, at 5:02 AM, Ian Campbell wrote:

> On Thu, 2012-09-13 at 17:09 +0100, Andres Lagar-Cavilla wrote:
>> tools/xenstore/xs.c |  22 ++++++----------------
>> 1 files changed, 6 insertions(+), 16 deletions(-)
>> 
>> 
>> Remove usage of pthread_cleanup_push and _pop, and explicitly call free for
>> heap objects in error paths. Also remove cleanup_p* for a mutex unlock path. 
>> By
>> the way, set a suitable errno value for an error path that had none.
>> 
>> Resend due to small fix spotted, please ignore previous one.
>> 
>> Signed-off-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>
> 
> Does this reintroduce the same issue as 21353:2dd3141b3e3e was supposed
> to solve (i.e. leaks memory or mutexes if you pthread_cancel the thread
> in the midst of things operation)?
Oh I never saw that coming. The approach below is what I would have done. Let 
me give that a try.
Andres

> 
> Can we keep cleanup_push/pop for use with the mutexes and for the
> malloc/free do:
> 
> #ifdef USE_PTHREAD
> #define cleanup_push... as currently
> #define cleanup_pop... as currently
> #define cleanup_malloc(x) cleanup_push(free, x)
> #define cleanup_free(doit, x)  cleanup_pop(doit)
> #else
> #define cleanup_push... nop as now
> #define cleanup_pop... nop as now
> #define cleanup_malloc... NOP
> #define cleanup_free(doit, x) if (doit) free(x)
> #endif
> 
> Does that work?
>> 
>> diff -r 588d0dc298a4 -r 9bfaf86e061f tools/xenstore/xs.c
>> --- a/tools/xenstore/xs.c
>> +++ b/tools/xenstore/xs.c
>> @@ -99,14 +99,6 @@ struct xs_handle {
>> #define mutex_unlock(m)              pthread_mutex_unlock(m)
>> #define condvar_signal(c)    pthread_cond_signal(c)
>> #define condvar_wait(c,m)    pthread_cond_wait(c,m)
>> -#define cleanup_push(f, a)  \
>> -    pthread_cleanup_push((void (*)(void *))(f), (void *)(a))
>> -/*
>> - * Some definitions of pthread_cleanup_pop() are a macro starting with an
>> - * end-brace. GCC then complains if we immediately precede that with a 
>> label.
>> - * Hence we insert a dummy statement to appease the compiler in this 
>> situation.
>> - */
>> -#define cleanup_pop(run)        ((void)0); pthread_cleanup_pop(run)
>> 
>> #define read_thread_exists(h)        (h->read_thr_exists)
>> 
>> @@ -126,8 +118,6 @@ struct xs_handle {
>> #define mutex_unlock(m)              ((void)0)
>> #define condvar_signal(c)    ((void)0)
>> #define condvar_wait(c,m)    ((void)0)
>> -#define cleanup_push(f, a)  ((void)0)
>> -#define cleanup_pop(run)    ((void)0)
>> #define read_thread_exists(h)        (0)
>> 
>> #endif
>> @@ -1059,7 +1049,6 @@ static int read_message(struct xs_handle
>>      msg = malloc(sizeof(*msg));
>>      if (msg == NULL)
>>              goto error;
>> -    cleanup_push(free, msg);
>>      if (!read_all(h->fd, &msg->hdr, sizeof(msg->hdr), nonblocking)) { /* 
>> Cancellation point */
>>              saved_errno = errno;
>>              goto error_freemsg;
>> @@ -1069,7 +1058,6 @@ static int read_message(struct xs_handle
>>      body = msg->body = malloc(msg->hdr.len + 1);
>>      if (body == NULL)
>>              goto error_freemsg;
>> -    cleanup_push(free, body);
>>      if (!read_all(h->fd, body, msg->hdr.len, 0)) { /* Cancellation point */
>>              saved_errno = errno;
>>              goto error_freebody;
>> @@ -1079,7 +1067,6 @@ static int read_message(struct xs_handle
>> 
>>      if (msg->hdr.type == XS_WATCH_EVENT) {
>>              mutex_lock(&h->watch_mutex);
>> -            cleanup_push(pthread_mutex_unlock, &h->watch_mutex);
>> 
>>              /* Kick users out of their select() loop. */
>>              if (list_empty(&h->watch_list) &&
>> @@ -1091,13 +1078,14 @@ static int read_message(struct xs_handle
>> 
>>              condvar_signal(&h->watch_condvar);
>> 
>> -            cleanup_pop(1);
>> +            mutex_unlock(&h->watch_mutex);
>>      } else {
>>              mutex_lock(&h->reply_mutex);
>> 
>>              /* There should only ever be one response pending! */
>>              if (!list_empty(&h->reply_list)) {
>>                      mutex_unlock(&h->reply_mutex);
>> +                    saved_errno = EEXIST; 
>>                      goto error_freebody;
>>              }
>> 
>> @@ -1110,9 +1098,11 @@ static int read_message(struct xs_handle
>>      ret = 0;
>> 
>> error_freebody:
>> -    cleanup_pop(ret == -1);
>> +    if (ret)
>> +            free(body);
>> error_freemsg:
>> -    cleanup_pop(ret == -1);
>> +    if (ret)
>> +            free(msg);
>> error:
>>      errno = saved_errno;
>> 
> 
> 


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