[lttng-dev] question about rcu_bp_exit()

[mathieu.desnoyers@efficios.com (Mathieu Desnoyers)]

----- On May 18, 2016, at 5:44 AM, songxin <songxin_1980 at 126.com> wrote: 

> Hi,
> Now I get a crash because receiving signal SIGSEGV as below.

> #0 arena_alloc (arena=<optimized out>) at
> /usr/src/debug/liburcu/0.9.1+git5fd33b1e5003ca316bd314ec3fd1447f6199a282-r0/git/urcu-bp.c:432
> #1 add_thread () at
> /usr/src/debug/liburcu/0.9.1+git5fd33b1e5003ca316bd314ec3fd1447f6199a282-r0/git/urcu-bp.c:462
> #2 rcu_bp_register () at
> /usr/src/debug/liburcu/0.9.1+git5fd33b1e5003ca316bd314ec3fd1447f6199a282-r0/git/urcu-bp.c:541

> I read the code of urcu-bp.c and found that "if (chunk->data_len - chunk->used <
> len)" is in 432 line. So I guess that the chunk is a illegal pointer.
> Below is the function rcu_bp_exit().

> static
> void rcu_bp_exit(void)
> {
> mutex_lock(&init_lock);
> if (!--rcu_bp_refcount) {
> struct registry_chunk *chunk, *tmp;
> int ret;

> cds_list_for_each_entry_safe(chunk, tmp,
> &registry_arena.chunk_list, node) {
> munmap(chunk, chunk->data_len
> + sizeof(struct registry_chunk));
> }
> ret = pthread_key_delete(urcu_bp_key);
> if (ret)
> abort();
> }
> mutex_unlock(&init_lock);
> }

> My question is below.
> Why did not delete the chunk from registry_arena.chunk_list before munmap a
> chunk?

It is not expected that any thread would be created after the execution of 
rcu_bp_exit() as a library destructor. Does re-initializing the chunk_list after 
iterating on it within rcu_bp_exit() fix your issue ? 

I'm curious about your use-case for creating threads after the library destructor 
has run. 

Thanks, 

Mathieu 

> Thanks,
> xin

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-- 
Mathieu Desnoyers 
EfficiOS Inc. 
http://www.efficios.com 
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