Re: [dpdk-dev] [PATCH] log: Properly reset log_history_size in rte_log_dump_history()

[Olivier MATZ <olivier.matz@6wind.com>]

Hi Jan,

On 05/29/2015 12:34 PM, Jan Blunck wrote:
> In rte_log_dump_history() the log_history list is reinitialized without
> resetting the log_history_size. In the next call to rte_log_add_in_history()
> the log_history_size > RTE_LOG_HISTORY and the code unconditionally tries
> to remove the first entry:
> 
> Program received signal SIGSEGV, Segmentation fault.
> rte_log_add_in_history (
>     buf=buf@entry=0x7f02035cd000 "DATAPLANE: 9:dp0s7 link RTM_NEWLINK [dp0s7] <UP,BROADCAST,RUNNING,MULTICAST,LOWER_UP>\nCAST,LOWER_UP>\n", size=size@entry=86)
>     at /usr/src/packages/BUILD/lib/librte_eal/common/eal_common_log.c:122
> 
> Signed-off-by: Jan Blunck <jblunck@infradead.org>
> ---
>  lib/librte_eal/common/eal_common_log.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/librte_eal/common/eal_common_log.c b/lib/librte_eal/common/eal_common_log.c
> index fe3d7d5..cb4311c 100644
> --- a/lib/librte_eal/common/eal_common_log.c
> +++ b/lib/librte_eal/common/eal_common_log.c
> @@ -119,7 +119,8 @@ rte_log_add_in_history(const char *buf, size_t size)
>  	/* get a buffer for adding in history */
>  	if (log_history_size > RTE_LOG_HISTORY) {
>  		hist_buf = STAILQ_FIRST(&log_history);
> -		STAILQ_REMOVE_HEAD(&log_history, next);
> +		if (hist_buf)
> +			STAILQ_REMOVE_HEAD(&log_history, next);

Shouldn't we decrease log_history_size here?



Also, it's probably a bit off-topic, but I think the function that
adds in history could be optimized a bit to avoid doing the copy with
the lock held. Maybe something like this is feasible:

rte_mempool_mc_get() into hist_buf
memcpy(hist_buf->buf, buf, size);
rte_spinlock_lock(&log_list_lock
if (log_history_size > RTE_LOG_HISTORY) {
    STAILQ_REMOVE_HEAD
    log_history_size --
}
STAILQ_INSERT_TAIL
log_history_size ++
rte_spinlock_unlock(&log_list_lock)

Feel free to implement it if you feel it's better. It would also
require to increase the number of objects in the pool to
RTE_LOG_HISTORY*2 + RTE_MAX_LCORE

Regards,
Olivier



>  	}
>  	else {
>  		if (rte_mempool_mc_get(log_history_mp, &obj) < 0)
> @@ -234,6 +235,7 @@ rte_log_dump_history(FILE *out)
>  	rte_spinlock_lock(&log_list_lock);
>  	tmp_log_history = log_history;
>  	STAILQ_INIT(&log_history);
> +	log_history_size = 0;
>  	rte_spinlock_unlock(&log_list_lock);
>  
>  	for (i=0; i<RTE_LOG_HISTORY; i++) {
>