Fix: statedump: invalid read during iter_end

Fix: statedump: invalid read during iter_end

Scenario
=========

Using a modified doc/examples/easy-ust/sample.c and dummy shared objects:

  int main(int argc, char **argv)
  {
  	int i = 0;

  	void *handle_cat;
  	void *handle_dog;
  	void (*func_print_name_cat)(const char*);
  	void (*func_print_name_dog)(const char*);

  	handle_dog = dlopen("./libdog.so", RTLD_NOW);
  	handle_cat = dlopen("./libcat.so", RTLD_NOW);

  	*(void**)(&func_print_name_dog) = dlsym(handle_dog, "print_name");
  	*(void**)(&func_print_name_cat) = dlsym(handle_cat, "print_name");

  	for (i = 0; i < 5; i++) {
  		tracepoint(sample_component, message, "Hello World");
  		usleep(1);
  	}

  	printf("Run `lttng regenerate statedump. Press enter \n");
  	getchar();

  	dlclose(handle_dog);
  	printf("Run `lttng regenerate statedump. Press enter \n");
  	getchar();

  	dlclose(handle_cat);

  	return 0;
  }

On lttng side:

 lttng create
 lttng enable-event -u -a
 lttng start

 valgrind sample

 Issue `lttng regenerate statedump` as the app suggest.

The second `lttng regenerate statedump` results in:

 ==934747== Invalid read of size 8
 ==934747==    at 0x48BA90F: iter_end (lttng-ust-statedump.c:439)
 ==934747==    by 0x48BAD73: lttng_ust_dl_update (lttng-ust-statedump.c:586)
 ==934747==    by 0x48BADC0: do_baddr_statedump (lttng-ust-statedump.c:599)
 ==934747==    by 0x48BAE62: do_lttng_ust_statedump (lttng-ust-statedump.c:633)
 ==934747==    by 0x489F820: lttng_handle_pending_statedump (lttng-events.c:969)
 ==934747==    by 0x488C000: handle_pending_statedump (lttng-ust-comm.c:717)
 ==934747==    by 0x488DCF7: handle_message (lttng-ust-comm.c:1110)
 ==934747==    by 0x48905EA: ust_listener_thread (lttng-ust-comm.c:1756)
 ==934747==    by 0x4B62608: start_thread (pthread_create.c:477)
 ==934747==    by 0x4A4D162: clone (clone.S:95)
 ==934747==  Address 0x4c4ea88 is 4,152 bytes inside a block of size 4,176 free'd
 ==934747==    at 0x483CA3F: free (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
 ==934747==    by 0x48B9588: free_dl_node (lttng-ust-statedump.c:123)
 ==934747==    by 0x48BA90A: iter_end (lttng-ust-statedump.c:450)
 ==934747==    by 0x48BAD73: lttng_ust_dl_update (lttng-ust-statedump.c:586)
 ==934747==    by 0x48BADC0: do_baddr_statedump (lttng-ust-statedump.c:599)
 ==934747==    by 0x48BAE62: do_lttng_ust_statedump (lttng-ust-statedump.c:633)
 ==934747==    by 0x489F820: lttng_handle_pending_statedump (lttng-events.c:969)
 ==934747==    by 0x488C000: handle_pending_statedump (lttng-ust-comm.c:717)
 ==934747==    by 0x488DCF7: handle_message (lttng-ust-comm.c:1110)
 ==934747==    by 0x48905EA: ust_listener_thread (lttng-ust-comm.c:1756)
 ==934747==    by 0x4B62608: start_thread (pthread_create.c:477)
 ==934747==    by 0x4A4D162: clone (clone.S:95)
 ==934747==  Block was alloc'd at
 ==934747==    at 0x483DD99: calloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
 ==934747==    by 0x48B936A: zmalloc (helper.h:27)
 ==934747==    by 0x48B936A: alloc_dl_node (lttng-ust-statedump.c:85)
 ==934747==    by 0x48B98F7: find_or_create_dl_node (lttng-ust-statedump.c:184)
 ==934747==    by 0x48BA205: extract_baddr (lttng-ust-statedump.c:339)
 ==934747==    by 0x48BABC6: extract_bin_info_events (lttng-ust-statedump.c:528)
 ==934747==    by 0x4A8D2F4: dl_iterate_phdr (dl-iteratephdr.c:75)
 ==934747==    by 0x48BAD4C: lttng_ust_dl_update (lttng-ust-statedump.c:583)
 ==934747==    by 0x48BADC0: do_baddr_statedump (lttng-ust-statedump.c:599)
 ==934747==    by 0x48BAE62: do_lttng_ust_statedump (lttng-ust-statedump.c:633)
 ==934747==    by 0x489F820: lttng_handle_pending_statedump (lttng-events.c:969)
 ==934747==    by 0x488C000: handle_pending_statedump (lttng-ust-comm.c:717)
 ==934747==    by 0x488DCF7: handle_message (lttng-ust-comm.c:1110)
 ==934747==

Cause
=========

Nodes can be removed during the `cds_hlist_for_each_entry_2` iteration which
is not meant to be used when items are removed within the traversal.

Solution
=========

Use `cds_hlist_for_each_entry_safe_2`.

Change-Id: Ibf3d94a4d6f7abac19ed9740eeacfbcb1bdf1f4f
Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>