git:master: dialog: Don't destroy dialogs in timer while they' re still being referenced
3 Nov
2014
3 Nov
'14
11:34 a.m.
Module: sip-router
Branch: master
Commit: 3eef4c8be5cc2b6ccba993a62f8c8039d1adf7da
URL:
http://git.sip-router.org/cgi-bin/gitweb.cgi/sip-router/?a=commit;h=3eef4c8…
Author: Alex Hermann <alex(a)speakup.nl>
Committer: Alex Hermann <alex(a)speakup.nl>
Date: Thu Oct 23 15:09:05 2014 +0200
dialog: Don't destroy dialogs in timer while they're still being referenced
---
modules/dialog/dlg_hash.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/modules/dialog/dlg_hash.c b/modules/dialog/dlg_hash.c
index 09166b8..31ad428 100644
--- a/modules/dialog/dlg_hash.c
+++ b/modules/dialog/dlg_hash.c
@@ -242,7 +242,7 @@ int dlg_clean_run(ticks_t ti)
while (dlg) {
tdlg = dlg;
dlg = dlg->next;
- if(tdlg->state==DLG_STATE_UNCONFIRMED && tdlg->init_ts<tm-300) {
+ if(tdlg->state==DLG_STATE_UNCONFIRMED && tdlg->init_ts<tm-300
&& tdlg->ref<=1) {
/* dialog in early state older than 5min */
LM_NOTICE("dialog in early state is too old (%p ref %d)\n",
tdlg, tdlg->ref);
3 Nov
3 Nov
4:07 p.m.
Hello,
what would be the situation to happen like that? Have you spotted a case
when an non established dialog lasting for more than 5 minutes is still
referenced externally by pointer? For cases when it can take many
minutes to come back to a dialog, the dialog ids should be cloned and
used for searching dialog when needed.
Cheers,
Daniel
On 03/11/14 10:34, Alex Hermann wrote:
Module: sip-router
Branch: master
Commit: 3eef4c8be5cc2b6ccba993a62f8c8039d1adf7da
URL:
http://git.sip-router.org/cgi-bin/gitweb.cgi/sip-router/?a=commit;h=3eef4c8…
Author: Alex Hermann <alex(a)speakup.nl>
Committer: Alex Hermann <alex(a)speakup.nl>
Date: Thu Oct 23 15:09:05 2014 +0200
dialog: Don't destroy dialogs in timer while they're still being referenced
---
modules/dialog/dlg_hash.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/modules/dialog/dlg_hash.c b/modules/dialog/dlg_hash.c
index 09166b8..31ad428 100644
--- a/modules/dialog/dlg_hash.c
+++ b/modules/dialog/dlg_hash.c
@@ -242,7 +242,7 @@ int dlg_clean_run(ticks_t ti)
while (dlg) {
tdlg = dlg;
dlg = dlg->next;
- if(tdlg->state==DLG_STATE_UNCONFIRMED && tdlg->init_ts<tm-300) {
+ if(tdlg->state==DLG_STATE_UNCONFIRMED && tdlg->init_ts<tm-300
&& tdlg->ref<=1) {
/* dialog in early state older than 5min */
LM_NOTICE("dialog in early state is too old (%p ref %d)\n",
tdlg, tdlg->ref);
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--
Daniel-Constantin Mierla
http://twitter.com/#!/miconda - http://www.linkedin.com/in/miconda
Kamailio Advanced Training, Nov 24-27, Berlin - http://www.asipto.com
5:32 p.m.
New subject: git:master: dialog: Don't destroy dialogs in timer while they' re still being referenced
On Monday 03 November 2014, Daniel-Constantin Mierla wrote:
what would be the situation to happen like that? Have
you spotted a case
when an non established dialog lasting for more than 5 minutes is still
referenced externally by pointer?
I had a segfault because another process was handling a very late reply. I
don't know the exact circumstances that led to it.
For cases when it can take many
minutes to come back to a dialog, the dialog ids should be cloned and
used for searching dialog when needed.
The whole idea of refcounting is not to hold a lock during processing, but
just during obtaining a pointer to the object. Refcounted objects should never
be deleted when they are still being referenced by others.
In this case, the process handling the reply behaved well and had upped the
refcounter. The timer process ignored the refcount and freed the object still
in use.
Now that i think of it, the proper thing to do here would probably be just to
unref the dlg instead of open-coding around it.
--
Greetings,
Alex Hermann
5:48 p.m.
On 03/11/14 16:32, Alex Hermann wrote:
On Monday 03 November 2014, Daniel-Constantin Mierla
wrote:
Reference counters are good as long as they are used in predictable
circumstances. The problem encountered so far were related to the fact
that not all calls have proper signaling (e.g., network issues, buggy
clients), the reason for this cleanup routine as well (i.e., also sip
protocol relies on a time interval for not receiving ACK).
My goal was to figure out what was the situation, see if it is something
predictable that can be fixed in source code -- dialogs staying too long
in a state that shouldn't take too long are susceptible to issues and it
is better if we know what was the reason.
Daniel
--
Daniel-Constantin Mierla
http://twitter.com/#!/miconda - http://www.linkedin.com/in/miconda
Kamailio Advanced Training, Nov 24-27, Berlin - http://www.asipto.com
what would be the situation to happen like that?
Have you spotted a case
when an non established dialog lasting for more than 5 minutes is still
referenced externally by pointer?
I had a segfault because another process was
handling a very late reply. I
don't know the exact circumstances that led to it.
For cases when it can take many
minutes to come back to a dialog, the dialog ids should be cloned and
used for searching dialog when needed.
The whole idea of refcounting is not to
hold a lock during processing, but
just during obtaining a pointer to the object. Refcounted objects should never
be deleted when they are still being referenced by others.
In this case, the process handling the reply behaved well and had upped the
refcounter. The timer process ignored the refcount and freed the object still
in use.
Now that i think of it, the proper thing to do here would probably be just to
unref the dlg instead of open-coding around it.
6:05 p.m.
New subject: git:master: dialog: Don't destroy dialogs in timer while they' re still being referenced
On Monday 03 November 2014, Daniel-Constantin Mierla wrote:
Reference counters are good as long as they are used
in predictable
circumstances. The problem encountered so far were related to the fact
that not all calls have proper signaling (e.g., network issues, buggy
clients), the reason for this cleanup routine as well
True. But even then refcounting shouldn't be bypassed. For each (cleanup)
situation the expected refcount should be compared to the actual refcount
before deleting.
For the situation at hand, if the refcount is >1, something is handling the
dlg (or has buggy code not unreffing after finishing).
I think my fix catches those situations tough. When the ACK is missing, the
refcount should be 1. When another process is handling the dlg, the refcount
will be >1.
(i.e., also sip
protocol relies on a time interval for not receiving ACK).
This specific situation is not about missing ACK. That would be
DLG_STATE_CONFIRMED_NA.
My goal was to figure out what was the situation, see
if it is something
predictable that can be fixed in source code -- dialogs staying too long
in a state that shouldn't take too long are susceptible to issues and it
is better if we know what was the reason.
It is weird that the TMCB_DESTROY callback didn't cleanup the dialog. I
haven't investigated the cause as i could fix the segfault pretty easily.
--
Greetings,
Alex Hermann
4 Nov
4 Nov
11:57 a.m.
On 03/11/14 17:05, Alex Hermann wrote:
It was a quick example that sip relies on time intervals for changing
states.
So far sounds like fixing something that we don't know what was and the
side effects are not good. I would like to get to a proper solution,
knowing what was the issue.
Cheers,
Daniel
--
Daniel-Constantin Mierla
http://twitter.com/#!/miconda - http://www.linkedin.com/in/miconda
Kamailio Advanced Training, Nov 24-27, Berlin - http://www.asipto.com
On Monday 03 November 2014, Daniel-Constantin Mierla
wrote:
Not sure what would be expected reference counter value in each of
the
states. The aim of the cleanup was to go beyond reasonable time a dialog
can stay in a state and clean up to avoid memory leaks.
Reference counters are good as long as they are
used in predictable
circumstances. The problem encountered so far were related to the fact
that not all calls have proper signaling (e.g., network issues, buggy
clients), the reason for this cleanup routine as well
True. But even then
refcounting shouldn't be bypassed. For each (cleanup)
situation the expected refcount should be compared to the actual refcount
before deleting. For the situation at hand, if the refcount is >1,
something is handling the
dlg (or has buggy code not unreffing after finishing).
In theory, the dialog cannot last for ever in initial state, so cleaning
it up make sense to stay safe of memory leaks at runtime -- we can print
log messages to alert, but keeping it for ever brings more troubles
(e.g., besides memory leaks, the call limit can be affected).
I think my fix catches those situations tough. When the ACK is missing, the
refcount should be 1. When another process is handling the dlg, the refcount
will be >1.
As I said, for operations that are long term, I consider better to keep
dlg index and label (two integers) than increasing the reference count
and storing the pointer (on 64b it is the same size). Then lookup again
the dialog when needed. Finding the reason of what determined you to do
this is important, not to push kind of workaround that we don't fully
understand its purpose and benefits.
IMO, it is not right to keep a dialog in proxy as long as caller/callee
don't have it anymore.
You can eventually make the behavior of the patch configurable, so you
can enable it via modparam, in the current form I don't find it ok.
(i.e., also sip
protocol relies on a time interval for not receiving ACK).
This specific situation
is not about missing ACK. That would be
DLG_STATE_CONFIRMED_NA. My goal was to figure out what was the situation,
see if it is something
predictable that can be fixed in source code -- dialogs staying too long
in a state that shouldn't take too long are susceptible to issues and it
is better if we know what was the reason.
It is weird that the TMCB_DESTROY
callback didn't cleanup the dialog. I
haven't investigated the cause as i could fix the segfault pretty easily.
3:19 p.m.
New subject: git:master: dialog: Don't destroy dialogs in timer while they' re still being referenced
On Tuesday 04 November 2014, Daniel-Constantin Mierla wrote:
I think it is necessary to know it to be able to securely cleanup dialogs.
It was a quick example that sip relies on time intervals for changing
states.
So far sounds like fixing something that we don't know what was and the
side effects are not good. I would like to get to a proper solution,
knowing what was the issue.
I'm sorry, but IMHO this (and earlier) argument applies more to your initial
cleanup routine for the stray dialogs than to my fix for the segfault.
--
Greetings,
Alex Hermann
On 03/11/14 17:05, Alex Hermann wrote:
> On Monday 03 November 2014, Daniel-Constantin Mierla wrote:
True. But even
then refcounting shouldn't be bypassed. For each (cleanup)
situation the expected refcount should be compared to the actual refcount
before deleting.
Not sure what would be expected reference counter value in each of the
states. In theory, the dialog cannot last for ever in initial
state, so cleaning
it up make sense to stay safe of memory leaks at runtime -- we can print
log messages to alert, but keeping it for ever brings more troubles
(e.g., besides memory leaks, the call limit can be affected).
I agree those must be cleaned, even though it is not technically a memory
leak, as the dialog pointer is still used in the dialog hash.
As I said, for operations that are long term, I
consider better to keep
dlg index and label (two integers) than increasing the reference count
and storing the pointer (on 64b it is the same size). Then lookup again
the dialog when needed.
Who is talking about "long term" operations? The duration is not of any
relevance here.
Almost none of the dialog related operations apart from getting the dlg
pointer are protected by locks but by the refcounter. Suppose process 1
obtains a dlg pointer (from the h_entry, and h_id), and upped the refcounter
as a result. It can get scheduled away at any random time, even directly after
obtaining the dlg pointer. If the timer process get scheduled at that moment
and frees the memory of the dlg (disregarding the fact that is is still in
use), how is process 1 to know that?
Finding the reason of what determined you to do
this is important, not to push kind of workaround that we don't fully
understand its purpose and benefits.
IMO, it is not right to keep a dialog in proxy as long as caller/callee
don't have it anymore.
I agree, just not with the method you used to get rid of the dialog.
You can eventually make the behavior of the patch
configurable, so you
can enable it via modparam, in the current form I don't find it ok.
I'm not going to make a known segfault path configurable, so i'll revert it if
you insist. But may i kindly suggest you revert your code too which introduced
this code in the first place as, IMHO, it is fundamentally wrong by deleting
an object without checking if it is in use.
(i.e., also sip
protocol relies on a time interval for not receiving ACK).
This specific situation is not about missing ACK. That would be
DLG_STATE_CONFIRMED_NA. My goal
was to figure out what was the situation, see if it is something
predictable that can be fixed in source code -- dialogs staying too long
in a state that shouldn't take too long are susceptible to issues and it
is better if we know what was the reason.
It is weird that the TMCB_DESTROY callback didn't cleanup the dialog. I
haven't investigated the cause as i could fix the segfault pretty easily.
3:48 p.m.
On 04/11/14 14:19, Alex Hermann wrote:
On Tuesday 04 November 2014, Daniel-Constantin Mierla
wrote:
If you discovered a flaw in existing code, then should be fixed
properly. It is what I am trying to do as well by discussing your patch.
This is the benefit of open source, reviewing patches for mutual
benefits, and I do hope other people check my commits as well.
I didn't say you didn't get an issue with it and the existing old code
was perfect, I am just trying to understand the issue and be sure it is
the right fix, with no side effects. I will be more than happy to solve
what you found as problem in the old patch, together we what I found not
clear with the last patch.
You said you don't have a backtrace for it and also you didn't provide
any further details about the situation, but now you refer to it as a
'known segfault'. If you can provide more info about the crash, it can
help to really solve the problem.
Just reverting and going back in another buggy state it is not good. I
expressed my opinions that with the patch, it seems we can get back to
the state with dialogs stuck in memory for ever. The config was more
like a temporary solution if you had any pressure on having the patch,
to give everyone an easy option to decide how to use it.
Otherwise, yes, I do want to get it properly fixed, with no options.
Cheers,
Daniel
--
Daniel-Constantin Mierla
http://twitter.com/#!/miconda - http://www.linkedin.com/in/miconda
Kamailio Advanced Training, Nov 24-27, Berlin - http://www.asipto.com
On 03/11/14 17:05, Alex Hermann wrote:
I think it is necessary to know it to be able to securely cleanup
dialogs.
On Monday 03 November 2014, Daniel-Constantin
Mierla wrote:
True. But even then refcounting shouldn't be bypassed. For each (cleanup)
situation the expected refcount should be compared to the actual refcount
before deleting.
Not sure what would be expected reference counter value in each
of the
states. In theory, the dialog cannot last for ever in
initial state, so cleaning
it up make sense to stay safe of memory leaks at runtime -- we can print
log messages to alert, but keeping it for ever brings more troubles
(e.g., besides memory leaks, the call limit can be affected).
I agree those must
be cleaned, even though it is not technically a memory
leak, as the dialog pointer is still used in the dialog hash.
As I said, for operations that are long term, I
consider better to keep
dlg index and label (two integers) than increasing the reference count
and storing the pointer (on 64b it is the same size). Then lookup again
the dialog when needed.
Who is talking about "long term" operations? The
duration is not of any
relevance here.
Almost none of the dialog related operations apart from getting the dlg
pointer are protected by locks but by the refcounter. Suppose process 1
obtains a dlg pointer (from the h_entry, and h_id), and upped the refcounter
as a result. It can get scheduled away at any random time, even directly after
obtaining the dlg pointer. If the timer process get scheduled at that moment
and frees the memory of the dlg (disregarding the fact that is is still in
use), how is process 1 to know that?
Finding the reason of what determined you to do
this is important, not to push kind of workaround that we don't fully
understand its purpose and benefits.
IMO, it is not right to keep a dialog in proxy as long as caller/callee
don't have it anymore.
I agree, just not with the method you used to get rid
of the dialog.
You can eventually make the behavior of the patch
configurable, so you
can enable it via modparam, in the current form I don't find it ok.
I'm
not going to make a known segfault path configurable, so i'll revert it if
you insist. But may i kindly suggest you revert your code too which introduced
this code in the first place as, IMHO, it is fundamentally wrong by deleting
an object without checking if it is in use.
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days inactive
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7 comments
2 participants
participants (2)
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