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<div class="moz-cite-prefix">On 9/17/2012 21:33 PM, Mathieu
Desnoyers wrote:<br>
</div>
<blockquote cite="mid:20120917133324.GC4256@Krystal" type="cite">
<pre wrap="">* changz (<a class="moz-txt-link-abbreviated" href="mailto:zheng.chang@emc.com">zheng.chang@emc.com</a>) wrote:
</pre>
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<pre wrap="">......
The child process calls _fini when it calls API exit. It gets hung and
meanwhile the parent is waiting for its termination.
I think the whole life-cycle of the process should be considered. The
parent's waiting in critical region is dangerous.
Is it possible to refine the critical region with smaller fineness?
What do you think?
</pre>
</blockquote>
<pre wrap="">
Hrm, yes you're right. I'm looking into it.
The main issue is that get_wait_shm() bypass the fork() wrapper (with
lttng_ust_nest_count), which is responsible for holding the UST mutex
across fork(). Therefore, when exiting the context of the child process,
we execute the destructor, which try to grab the UST mutex, which might
be in pretty much any state.
Given that we don't want this process to try to register to
lttng-sessiond (because this is internal to lttng-ust), we might want to
let it skip the destructor execution. This would actually be the easiest
way out.
Does the follow patch fix the issue for you ?
diff --git a/liblttng-ust/lttng-ust-comm.c b/liblttng-ust/lttng-ust-comm.c
index be64acd..596fd7d 100644
--- a/liblttng-ust/lttng-ust-comm.c
+++ b/liblttng-ust/lttng-ust-comm.c
@@ -616,9 +616,9 @@ int get_wait_shm(struct sock_info *sock_info, size_t mmap_size)
ret = ftruncate(wait_shm_fd, mmap_size);
if (ret) {
PERROR("ftruncate");
- exit(EXIT_FAILURE);
+ _exit(EXIT_FAILURE);
}
- exit(EXIT_SUCCESS);
+ _exit(EXIT_SUCCESS);
}
/*
* For local shm, we need to have rw access to accept
</pre>
</blockquote>
Yes, it works. <br>
Just a reminder, here are<big> four</big> callings of exit in
child's path in my git repository.<br>
<br>
Thanks & BR<br>
-Zheng<br>
<br>
<blockquote cite="mid:20120917133324.GC4256@Krystal" type="cite">
<pre wrap="">
</pre>
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<br>
<br>
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