[lttng-dev] [PATCH babeltrace 1.5] Use trace->trace_id for check to remove trace from bt_ctx

[Jonathan Rajotte-Julien]

On Tue, Jul 03, 2018 at 12:28:54PM -0400, Jonathan Rajotte wrote:
> Commit b9e6498df8b3e7c2ad312dccddf9f1a5e181648e remove the existence
> guarantee of the trace_id hash table key by moving the trace->in_use
> assignation before the assignation of trace_id and insertion into
> the hash table.
> 
> Use the trade_id field value to validate if it should be
> removed from the hash table.
> A NULL trace_id field indicates that no insertion was performed.

This is not true since trace_id start at zero. A solution to this is to start
the trace_id numbering a 1.

> 
> This is mostly a workaround to a problem found in, at least, glib-2.28
> where the g_hash_table_lookup_node abort on a SIGFPE signal due to
> modulo by zero. The exact cause for this is unknown for now [1].
> There is little reason for "mod" to be 0 at that point as explained in
> the bug report.
> 
> Currently unable to reproduce.
> 
> [1] https://bugzilla.redhat.com/show_bug.cgi?id=1074401
> 
> Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien at efficios.com>
> ---
>  formats/lttng-live/lttng-live-comm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/formats/lttng-live/lttng-live-comm.c b/formats/lttng-live/lttng-live-comm.c
> index 055b1c30..941d5c2f 100644
> --- a/formats/lttng-live/lttng-live-comm.c
> +++ b/formats/lttng-live/lttng-live-comm.c
> @@ -1466,7 +1466,7 @@ int del_traces(gpointer key, gpointer value, gpointer user_data)
>  		lvstream->in_trace = 0;
>  		bt_list_del(&lvstream->trace_stream_node);
>  	}
> -	if (trace->in_use) {
> +	if (trace->in_use && trace->trace_id) {
>  		ret = bt_context_remove_trace(bt_ctx, trace->trace_id);
>  		if (ret < 0)
>  			fprintf(stderr, "[error] removing trace from context\n");
> -- 
> 2.17.1
> 

-- 
Jonathan Rajotte-Julien
EfficiOS