[ltt-dev] [UST PATCH] libust: Fix multiple fd close during fork

[ltt-dev] [UST PATCH] libust: Fix multiple fd close during fork

[Nils Carlson]

Remove superfluous fd closes during fork and also destroy all
traces instead of just "auto".

Reported-by: Yannick Brosseau <yannick.brosseau at gmail.com>
Signed-off-by: Nils Carlson <nils.carlson at ericsson.com>
---
 libust/tracectl.c |   17 ++++++++---------
 1 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/libust/tracectl.c b/libust/tracectl.c
index 1bd7229..1fc0118 100644
--- a/libust/tracectl.c
+++ b/libust/tracectl.c
@@ -1569,6 +1569,7 @@ static void ust_fork(void)
 {
 	struct ust_buffer *buf, *buf_tmp;
 	struct ustcomm_sock *sock, *sock_tmp;
+	struct ust_trace *trace, *trace_tmp;
 	int result;
 
 	/* FIXME: technically, the locks could have been taken before the fork */
@@ -1589,18 +1590,16 @@ static void ust_fork(void)
 	/* Delete all blocked consumers */
 	cds_list_for_each_entry_safe(buf, buf_tmp, &open_buffers_list,
 				 open_buffers_list) {
-		result = close(buf->data_ready_fd_read);
-		if (result == -1) {
-			PERROR("close");
-		}
-		result = close(buf->data_ready_fd_write);
-		if (result == -1) {
-			PERROR("close");
-		}
 		cds_list_del(&buf->open_buffers_list);
 	}
 
-	ltt_trace_destroy("auto", 1);
+	/*
+	 * FIXME: This could be prettier, we loop over the list twice and
+	 * following good locking practice should lock around the loop
+	 */
+	cds_list_for_each_entry_safe(trace, trace_tmp, &ltt_traces.head, list) {
+		ltt_trace_destroy(trace->trace_name, 1);
+	}
 
 	/* Clean up the listener socket and epoll, keeping the scoket file */
 	ustcomm_del_named_sock(listen_sock, 1);
-- 
1.7.1

[ltt-dev] [UST PATCH] libust: Fix multiple fd close during fork

[Nils Carlson]

This sort of fixes things in a wider sense as with the original patch we 
might leave trailing fds open and a non "auto" trace would have been 
neither destroyed nor have its fds closed...

Hope its ok with you yannick. Keep up the good work!

/Nils

On Wed, 23 Feb 2011, Nils Carlson wrote:

> Remove superfluous fd closes during fork and also destroy all
> traces instead of just "auto".
>
> Reported-by: Yannick Brosseau <yannick.brosseau at gmail.com>
> Signed-off-by: Nils Carlson <nils.carlson at ericsson.com>
> ---
> libust/tracectl.c |   17 ++++++++---------
> 1 files changed, 8 insertions(+), 9 deletions(-)
>
> diff --git a/libust/tracectl.c b/libust/tracectl.c
> index 1bd7229..1fc0118 100644
> --- a/libust/tracectl.c
> +++ b/libust/tracectl.c
> @@ -1569,6 +1569,7 @@ static void ust_fork(void)
> {
> 	struct ust_buffer *buf, *buf_tmp;
> 	struct ustcomm_sock *sock, *sock_tmp;
> +	struct ust_trace *trace, *trace_tmp;
> 	int result;
>
> 	/* FIXME: technically, the locks could have been taken before the fork */
> @@ -1589,18 +1590,16 @@ static void ust_fork(void)
> 	/* Delete all blocked consumers */
> 	cds_list_for_each_entry_safe(buf, buf_tmp, &open_buffers_list,
> 				 open_buffers_list) {
> -		result = close(buf->data_ready_fd_read);
> -		if (result == -1) {
> -			PERROR("close");
> -		}
> -		result = close(buf->data_ready_fd_write);
> -		if (result == -1) {
> -			PERROR("close");
> -		}
> 		cds_list_del(&buf->open_buffers_list);
> 	}
>
> -	ltt_trace_destroy("auto", 1);
> +	/*
> +	 * FIXME: This could be prettier, we loop over the list twice and
> +	 * following good locking practice should lock around the loop
> +	 */
> +	cds_list_for_each_entry_safe(trace, trace_tmp, &ltt_traces.head, list) {
> +		ltt_trace_destroy(trace->trace_name, 1);
> +	}
>
> 	/* Clean up the listener socket and epoll, keeping the scoket file */
> 	ustcomm_del_named_sock(listen_sock, 1);
> -- 
> 1.7.1
>
>

[ltt-dev] [UST PATCH] libust: Fix multiple fd close during fork

[Yannick Brosseau]

On 2011-02-23 07:43, Nils Carlson wrote:
>
> This sort of fixes things in a wider sense as with the original patch
> we might leave trailing fds open and a non "auto" trace would have
> been neither destroyed nor have its fds closed...
>
> Hope its ok with you yannick. Keep up the good work!

that's fine with me. But shouldn't we also do this kind of loop for all
the "auto" in the ust_fork function?

>
> /Nils
>
> On Wed, 23 Feb 2011, Nils Carlson wrote:
>
>> Remove superfluous fd closes during fork and also destroy all
>> traces instead of just "auto".
>>
>> Reported-by: Yannick Brosseau <yannick.brosseau at gmail.com>
>> Signed-off-by: Nils Carlson <nils.carlson at ericsson.com>
>> ---
>> libust/tracectl.c |   17 ++++++++---------
>> 1 files changed, 8 insertions(+), 9 deletions(-)
>>
>> diff --git a/libust/tracectl.c b/libust/tracectl.c
>> index 1bd7229..1fc0118 100644
>> --- a/libust/tracectl.c
>> +++ b/libust/tracectl.c
>> @@ -1569,6 +1569,7 @@ static void ust_fork(void)
>> {
>>     struct ust_buffer *buf, *buf_tmp;
>>     struct ustcomm_sock *sock, *sock_tmp;
>> +    struct ust_trace *trace, *trace_tmp;
>>     int result;
>>
>>     /* FIXME: technically, the locks could have been taken before the
>> fork */
>> @@ -1589,18 +1590,16 @@ static void ust_fork(void)
>>     /* Delete all blocked consumers */
>>     cds_list_for_each_entry_safe(buf, buf_tmp, &open_buffers_list,
>>                  open_buffers_list) {
>> -        result = close(buf->data_ready_fd_read);
>> -        if (result == -1) {
>> -            PERROR("close");
>> -        }
>> -        result = close(buf->data_ready_fd_write);
>> -        if (result == -1) {
>> -            PERROR("close");
>> -        }
>>         cds_list_del(&buf->open_buffers_list);
>>     }
>>
>> -    ltt_trace_destroy("auto", 1);
>> +    /*
>> +     * FIXME: This could be prettier, we loop over the list twice and
>> +     * following good locking practice should lock around the loop
>> +     */
>> +    cds_list_for_each_entry_safe(trace, trace_tmp, &ltt_traces.head,
>> list) {
>> +        ltt_trace_destroy(trace->trace_name, 1);
>> +    }
>>
>>     /* Clean up the listener socket and epoll, keeping the scoket
>> file */
>>     ustcomm_del_named_sock(listen_sock, 1);
>> -- 
>> 1.7.1
>>
>>

[ltt-dev] [UST PATCH] libust: Fix multiple fd close during fork

[Mathieu Desnoyers]

* Nils Carlson (nils.carlson at ericsson.com) wrote:
> Yep. fixed. merged.
>
>>>> +    /*
>>>> +     * FIXME: This could be prettier, we loop over the list twice and
>>>> +     * following good locking practice should lock around the loop
>>>> +     */
>>>> +    cds_list_for_each_entry_safe(trace, trace_tmp, &ltt_traces.head,
>>>> list) {
>>>> +        ltt_trace_destroy(trace->trace_name, 1);
>>>> +    }

So what' up with these missing locks ?

Mathieu

>>>>
>>>>     /* Clean up the listener socket and epoll, keeping the scoket
>>>> file */
>>>>     ustcomm_del_named_sock(listen_sock, 1);
>>>> --
>>>> 1.7.1
>>>>
>>>>
>>
>>
>
> _______________________________________________
> ltt-dev mailing list
> ltt-dev at lists.casi.polymtl.ca
> http://lists.casi.polymtl.ca/cgi-bin/mailman/listinfo/ltt-dev
>

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com

[ltt-dev] [UST PATCH] libust: Fix multiple fd close during fork

[Mathieu Desnoyers]

* Nils Carlson (nils.carlson at ericsson.com) wrote:
> On Wed, 23 Feb 2011, Mathieu Desnoyers wrote:
>
>> * Nils Carlson (nils.carlson at ericsson.com) wrote:
>>> Yep. fixed. merged.
>>>
>>>>>> +    /*
>>>>>> +     * FIXME: This could be prettier, we loop over the list twice and
>>>>>> +     * following good locking practice should lock around the loop
>>>>>> +     */
>>>>>> +    cds_list_for_each_entry_safe(trace, trace_tmp, &ltt_traces.head,
>>>>>> list) {
>>>>>> +        ltt_trace_destroy(trace->trace_name, 1);
>>>>>> +    }
>>
>> So what' up with these missing locks ?
>>
>
> They are actually taken by each ltt_trace_destroy. Also, this function is 
> run as part of the ust_fork so locking in the child is a non-issue at 
> this point. Its mostly an aesthetic thing that we should be consistent in 
> dealing with locks.

Most of the ust_fork code should actually be protected by a mutex to
deal with the fact that we might have a concurrent libust thread running
in the parent at the exact point we do the fork, thus letting the child
in a state where locks are taken, and waits on the locks forever,
because the libust thread is not present in the child. The concurrent
libust thread in the parent should be kept quiescent while we do the
fork.

I don't think this is handled at the moment, and can leave us with
various of the other locks in a "held" state when we run in the child.

Thoughts ?

Mathieu

>
> /Nils
>
>> Mathieu
>>
>>>>>>
>>>>>>     /* Clean up the listener socket and epoll, keeping the scoket
>>>>>> file */
>>>>>>     ustcomm_del_named_sock(listen_sock, 1);
>>>>>> --
>>>>>> 1.7.1
>>>>>>
>>>>>>
>>>>
>>>>
>>>
>>> _______________________________________________
>>> ltt-dev mailing list
>>> ltt-dev at lists.casi.polymtl.ca
>>> http://lists.casi.polymtl.ca/cgi-bin/mailman/listinfo/ltt-dev
>>>
>>
>> -- 
>> Mathieu Desnoyers
>> Operating System Efficiency R&D Consultant
>> EfficiOS Inc.
>> http://www.efficios.com
>>
>

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com

[ltt-dev] [UST PATCH] libust: Fix multiple fd close during fork

[Nils Carlson]

Yep. fixed. merged.

/Nils

On Wed, 23 Feb 2011, Yannick Brosseau wrote:

> On 2011-02-23 07:43, Nils Carlson wrote:
>>
>> This sort of fixes things in a wider sense as with the original patch
>> we might leave trailing fds open and a non "auto" trace would have
>> been neither destroyed nor have its fds closed...
>>
>> Hope its ok with you yannick. Keep up the good work!
>
> that's fine with me. But shouldn't we also do this kind of loop for all
> the "auto" in the ust_fork function?
>
>>
>> /Nils
>>
>> On Wed, 23 Feb 2011, Nils Carlson wrote:
>>
>>> Remove superfluous fd closes during fork and also destroy all
>>> traces instead of just "auto".
>>>
>>> Reported-by: Yannick Brosseau <yannick.brosseau at gmail.com>
>>> Signed-off-by: Nils Carlson <nils.carlson at ericsson.com>
>>> ---
>>> libust/tracectl.c |   17 ++++++++---------
>>> 1 files changed, 8 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/libust/tracectl.c b/libust/tracectl.c
>>> index 1bd7229..1fc0118 100644
>>> --- a/libust/tracectl.c
>>> +++ b/libust/tracectl.c
>>> @@ -1569,6 +1569,7 @@ static void ust_fork(void)
>>> {
>>>     struct ust_buffer *buf, *buf_tmp;
>>>     struct ustcomm_sock *sock, *sock_tmp;
>>> +    struct ust_trace *trace, *trace_tmp;
>>>     int result;
>>>
>>>     /* FIXME: technically, the locks could have been taken before the
>>> fork */
>>> @@ -1589,18 +1590,16 @@ static void ust_fork(void)
>>>     /* Delete all blocked consumers */
>>>     cds_list_for_each_entry_safe(buf, buf_tmp, &open_buffers_list,
>>>                  open_buffers_list) {
>>> -        result = close(buf->data_ready_fd_read);
>>> -        if (result == -1) {
>>> -            PERROR("close");
>>> -        }
>>> -        result = close(buf->data_ready_fd_write);
>>> -        if (result == -1) {
>>> -            PERROR("close");
>>> -        }
>>>         cds_list_del(&buf->open_buffers_list);
>>>     }
>>>
>>> -    ltt_trace_destroy("auto", 1);
>>> +    /*
>>> +     * FIXME: This could be prettier, we loop over the list twice and
>>> +     * following good locking practice should lock around the loop
>>> +     */
>>> +    cds_list_for_each_entry_safe(trace, trace_tmp, &ltt_traces.head,
>>> list) {
>>> +        ltt_trace_destroy(trace->trace_name, 1);
>>> +    }
>>>
>>>     /* Clean up the listener socket and epoll, keeping the scoket
>>> file */
>>>     ustcomm_del_named_sock(listen_sock, 1);
>>> --
>>> 1.7.1
>>>
>>>
>
>

[ltt-dev] [UST PATCH] libust: Fix multiple fd close during fork

[Nils Carlson]

On Wed, 23 Feb 2011, Mathieu Desnoyers wrote:

> * Nils Carlson (nils.carlson at ericsson.com) wrote:
>> Yep. fixed. merged.
>>
>>>>> +    /*
>>>>> +     * FIXME: This could be prettier, we loop over the list twice and
>>>>> +     * following good locking practice should lock around the loop
>>>>> +     */
>>>>> +    cds_list_for_each_entry_safe(trace, trace_tmp, &ltt_traces.head,
>>>>> list) {
>>>>> +        ltt_trace_destroy(trace->trace_name, 1);
>>>>> +    }
>
> So what' up with these missing locks ?
>

They are actually taken by each ltt_trace_destroy. Also, this function is 
run as part of the ust_fork so locking in the child is a non-issue at this 
point. Its mostly an aesthetic thing that we should be consistent in 
dealing with locks.

/Nils

> Mathieu
>
>>>>>
>>>>>     /* Clean up the listener socket and epoll, keeping the scoket
>>>>> file */
>>>>>     ustcomm_del_named_sock(listen_sock, 1);
>>>>> --
>>>>> 1.7.1
>>>>>
>>>>>
>>>
>>>
>>
>> _______________________________________________
>> ltt-dev mailing list
>> ltt-dev at lists.casi.polymtl.ca
>> http://lists.casi.polymtl.ca/cgi-bin/mailman/listinfo/ltt-dev
>>
>
> -- 
> Mathieu Desnoyers
> Operating System Efficiency R&D Consultant
> EfficiOS Inc.
> http://www.efficios.com
>

[ltt-dev] [UST PATCH] libust: Fix multiple fd close during fork

[Nils Carlson]

On Wed, 23 Feb 2011, Mathieu Desnoyers wrote:

> * Nils Carlson (nils.carlson at ericsson.com) wrote:
>> On Wed, 23 Feb 2011, Mathieu Desnoyers wrote:
>>
>>> * Nils Carlson (nils.carlson at ericsson.com) wrote:
>>>> Yep. fixed. merged.
>>>>
>>>>>>> +    /*
>>>>>>> +     * FIXME: This could be prettier, we loop over the list twice and
>>>>>>> +     * following good locking practice should lock around the loop
>>>>>>> +     */
>>>>>>> +    cds_list_for_each_entry_safe(trace, trace_tmp, &ltt_traces.head,
>>>>>>> list) {
>>>>>>> +        ltt_trace_destroy(trace->trace_name, 1);
>>>>>>> +    }
>>>
>>> So what' up with these missing locks ?
>>>
>>
>> They are actually taken by each ltt_trace_destroy. Also, this function is
>> run as part of the ust_fork so locking in the child is a non-issue at
>> this point. Its mostly an aesthetic thing that we should be consistent in
>> dealing with locks.
>
> Most of the ust_fork code should actually be protected by a mutex to
> deal with the fact that we might have a concurrent libust thread running
> in the parent at the exact point we do the fork, thus letting the child
> in a state where locks are taken, and waits on the locks forever,
> because the libust thread is not present in the child. The concurrent
> libust thread in the parent should be kept quiescent while we do the
> fork.
>

ust_fork is only called by the child after the fork. The function name is 
a bit misleading.

> I don't think this is handled at the moment, and can leave us with
> various of the other locks in a "held" state when we run in the child.

As far as locking is concerned we're completely safe today, as we are 
completely serialised. If we ever decide on multiple control threads or 
some such we will probably have to recheck all the locking.

/Nils


> Thoughts ?
>
> Mathieu
>
>>
>> /Nils
>>
>>> Mathieu
>>>
>>>>>>>
>>>>>>>     /* Clean up the listener socket and epoll, keeping the scoket
>>>>>>> file */
>>>>>>>     ustcomm_del_named_sock(listen_sock, 1);
>>>>>>> --
>>>>>>> 1.7.1
>>>>>>>
>>>>>>>
>>>>>
>>>>>
>>>>
>>>> _______________________________________________
>>>> ltt-dev mailing list
>>>> ltt-dev at lists.casi.polymtl.ca
>>>> http://lists.casi.polymtl.ca/cgi-bin/mailman/listinfo/ltt-dev
>>>>
>>>
>>> --
>>> Mathieu Desnoyers
>>> Operating System Efficiency R&D Consultant
>>> EfficiOS Inc.
>>> http://www.efficios.com
>>>
>>
>
> -- 
> Mathieu Desnoyers
> Operating System Efficiency R&D Consultant
> EfficiOS Inc.
> http://www.efficios.com
>

[ltt-dev] [UST PATCH] libust: Fix multiple fd close during fork

[Mathieu Desnoyers]

* Nils Carlson (nils.carlson at ericsson.com) wrote:
>
>
> On Wed, 23 Feb 2011, Mathieu Desnoyers wrote:
>
>> * Nils Carlson (nils.carlson at ericsson.com) wrote:
>>> On Wed, 23 Feb 2011, Mathieu Desnoyers wrote:
>>>
>>>> * Nils Carlson (nils.carlson at ericsson.com) wrote:
>>>>> Yep. fixed. merged.
>>>>>
>>>>>>>> +    /*
>>>>>>>> +     * FIXME: This could be prettier, we loop over the list twice and
>>>>>>>> +     * following good locking practice should lock around the loop
>>>>>>>> +     */
>>>>>>>> +    cds_list_for_each_entry_safe(trace, trace_tmp, &ltt_traces.head,
>>>>>>>> list) {
>>>>>>>> +        ltt_trace_destroy(trace->trace_name, 1);
>>>>>>>> +    }
>>>>
>>>> So what' up with these missing locks ?
>>>>
>>>
>>> They are actually taken by each ltt_trace_destroy. Also, this function is
>>> run as part of the ust_fork so locking in the child is a non-issue at
>>> this point. Its mostly an aesthetic thing that we should be consistent in
>>> dealing with locks.
>>
>> Most of the ust_fork code should actually be protected by a mutex to
>> deal with the fact that we might have a concurrent libust thread running
>> in the parent at the exact point we do the fork, thus letting the child
>> in a state where locks are taken, and waits on the locks forever,
>> because the libust thread is not present in the child. The concurrent
>> libust thread in the parent should be kept quiescent while we do the
>> fork.
>>
>
> ust_fork is only called by the child after the fork. The function name is 
> a bit misleading.
>
>> I don't think this is handled at the moment, and can leave us with
>> various of the other locks in a "held" state when we run in the child.
>
> As far as locking is concerned we're completely safe today, as we are  
> completely serialised. If we ever decide on multiple control threads or  
> some such we will probably have to recheck all the locking.

Let's look at:

ustfork.c:

Parent                           Child

fork()
  ust_before_fork()
    - disable signals
  plibc_func(); (real fork)
  ust_after_fork_parent()
    - restore signals
                                 ust_after_fork_child()
                                   - ust_fork()
                                       ltt_unlock_traces(); <- bug (never locked ?)
                                   - reenable signals

So if we have a libust listener thread running in the parent in parallel
with the fork(), we possibly leave many locks in "held" state when the
child starts, and we don't want that, right ? It looks like a can of
worms ready to be opened. Ideally, we should exclude the libust listener
thread by taking a mutex across the fork in ust_before_fork (after
disabling signals) and releasing it in both ust_after_fork_parent and
ust_after_fork_child.

Thoughts ?

Mathieu


>
> /Nils
>
>
>> Thoughts ?
>>
>> Mathieu
>>
>>>
>>> /Nils
>>>
>>>> Mathieu
>>>>
>>>>>>>>
>>>>>>>>     /* Clean up the listener socket and epoll, keeping the scoket
>>>>>>>> file */
>>>>>>>>     ustcomm_del_named_sock(listen_sock, 1);
>>>>>>>> --
>>>>>>>> 1.7.1
>>>>>>>>
>>>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> ltt-dev mailing list
>>>>> ltt-dev at lists.casi.polymtl.ca
>>>>> http://lists.casi.polymtl.ca/cgi-bin/mailman/listinfo/ltt-dev
>>>>>
>>>>
>>>> --
>>>> Mathieu Desnoyers
>>>> Operating System Efficiency R&D Consultant
>>>> EfficiOS Inc.
>>>> http://www.efficios.com
>>>>
>>>
>>
>> -- 
>> Mathieu Desnoyers
>> Operating System Efficiency R&D Consultant
>> EfficiOS Inc.
>> http://www.efficios.com
>>
>

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com

[ltt-dev] [UST PATCH] libust: Fix multiple fd close during fork

[Nils Carlson]

On Wed, 23 Feb 2011, Mathieu Desnoyers wrote:

> * Nils Carlson (nils.carlson at ericsson.com) wrote:
>>
>>
>> On Wed, 23 Feb 2011, Mathieu Desnoyers wrote:
>>
>>> * Nils Carlson (nils.carlson at ericsson.com) wrote:
>>>> On Wed, 23 Feb 2011, Mathieu Desnoyers wrote:
>>>>
>>>>> * Nils Carlson (nils.carlson at ericsson.com) wrote:
>>>>>> Yep. fixed. merged.
>>>>>>
>>>>>>>>> +    /*
>>>>>>>>> +     * FIXME: This could be prettier, we loop over the list twice and
>>>>>>>>> +     * following good locking practice should lock around the loop
>>>>>>>>> +     */
>>>>>>>>> +    cds_list_for_each_entry_safe(trace, trace_tmp, &ltt_traces.head,
>>>>>>>>> list) {
>>>>>>>>> +        ltt_trace_destroy(trace->trace_name, 1);
>>>>>>>>> +    }
>>>>>
>>>>> So what' up with these missing locks ?
>>>>>
>>>>
>>>> They are actually taken by each ltt_trace_destroy. Also, this function is
>>>> run as part of the ust_fork so locking in the child is a non-issue at
>>>> this point. Its mostly an aesthetic thing that we should be consistent in
>>>> dealing with locks.
>>>
>>> Most of the ust_fork code should actually be protected by a mutex to
>>> deal with the fact that we might have a concurrent libust thread running
>>> in the parent at the exact point we do the fork, thus letting the child
>>> in a state where locks are taken, and waits on the locks forever,
>>> because the libust thread is not present in the child. The concurrent
>>> libust thread in the parent should be kept quiescent while we do the
>>> fork.
>>>
>>
>> ust_fork is only called by the child after the fork. The function name is
>> a bit misleading.
>>
>>> I don't think this is handled at the moment, and can leave us with
>>> various of the other locks in a "held" state when we run in the child.
>>
>> As far as locking is concerned we're completely safe today, as we are
>> completely serialised. If we ever decide on multiple control threads or
>> some such we will probably have to recheck all the locking.
>
> Let's look at:
>
> ustfork.c:
>
> Parent                           Child
>
> fork()
>  ust_before_fork()
>    - disable signals
>  plibc_func(); (real fork)
>  ust_after_fork_parent()
>    - restore signals
>                                 ust_after_fork_child()
>                                   - ust_fork()
>                                       ltt_unlock_traces(); <- bug (never locked ?)
>                                   - reenable signals
>
> So if we have a libust listener thread running in the parent in parallel
> with the fork(), we possibly leave many locks in "held" state when the
> child starts, and we don't want that, right ? It looks like a can of
> worms ready to be opened. Ideally, we should exclude the libust listener
> thread by taking a mutex across the fork in ust_before_fork (after
> disabling signals) and releasing it in both ust_after_fork_parent and
> ust_after_fork_child.

I can have a look tomorrow. We don't have all that many locks though. Most 
of my focus has been on not causing deadlocks. I've sort of ducked the 
fork issue this far as their are some things to consider.

I think your solution of a cross-fork mutex is a good one. This would 
allow us to avoid the current pitfalls with memory allocation (currently 
if you fork before saving a reference to the allocated memory somewhere it 
will be lost resulting in a leak.)

Yepp. Think thats a good solution. Will think about it tonight. :-)

/Nils


> Thoughts ?
>
> Mathieu
>
>
>>
>> /Nils
>>
>>
>>> Thoughts ?
>>>
>>> Mathieu
>>>
>>>>
>>>> /Nils
>>>>
>>>>> Mathieu
>>>>>
>>>>>>>>>
>>>>>>>>>     /* Clean up the listener socket and epoll, keeping the scoket
>>>>>>>>> file */
>>>>>>>>>     ustcomm_del_named_sock(listen_sock, 1);
>>>>>>>>> --
>>>>>>>>> 1.7.1
>>>>>>>>>
>>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> ltt-dev mailing list
>>>>>> ltt-dev at lists.casi.polymtl.ca
>>>>>> http://lists.casi.polymtl.ca/cgi-bin/mailman/listinfo/ltt-dev
>>>>>>
>>>>>
>>>>> --
>>>>> Mathieu Desnoyers
>>>>> Operating System Efficiency R&D Consultant
>>>>> EfficiOS Inc.
>>>>> http://www.efficios.com
>>>>>
>>>>
>>>
>>> --
>>> Mathieu Desnoyers
>>> Operating System Efficiency R&D Consultant
>>> EfficiOS Inc.
>>> http://www.efficios.com
>>>
>>
>
> -- 
> Mathieu Desnoyers
> Operating System Efficiency R&D Consultant
> EfficiOS Inc.
> http://www.efficios.com
>