[DTrace-devel] [PATCH v2] Free the DIFO for a probe once it is loaded

[Eugene Loh]

Reviewed-by: Eugene Loh <eugene.loh at oracle.com>

On 7/25/25 15:34, Kris Van Hees via DTrace-devel wrote:
> When a lot of probes are being probed, keeping all DIFO around consumes
> a lot of memory.  Once the BPF program is loaded, the DIFO can be freed.
>
> Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
> ---
>   libdtrace/dt_bpf.c         | 26 +++++++++++++++++++-------
>   libdtrace/dt_prov_uprobe.c | 22 +++++++++++++++-------
>   2 files changed, 34 insertions(+), 14 deletions(-)
>
> diff --git a/libdtrace/dt_bpf.c b/libdtrace/dt_bpf.c
> index ccec8b43..ad8cc0e1 100644
> --- a/libdtrace/dt_bpf.c
> +++ b/libdtrace/dt_bpf.c
> @@ -1339,6 +1339,7 @@ dt_bpf_load_progs(dtrace_hdl_t *dtp, uint_t cflags)
>   	 */
>   	dtrace_getopt(dtp, "destructive", &dest_ok);
>   
> +	dp = NULL;
>   	for (prp = dt_list_next(&dtp->dt_enablings); prp != NULL;
>   	     prp = dt_list_next(prp)) {
>   		int		fd;
> @@ -1353,28 +1354,39 @@ dt_bpf_load_progs(dtrace_hdl_t *dtp, uint_t cflags)
>   			continue;
>   
>   		if (dt_link(dtp, prp, dp, NULL) == -1)
> -			return -1;
> +			goto fail;
>   
>   		DT_DISASM_PROG_LINKED(dtp, cflags, dp, stderr, NULL, prp->desc);
>   
>   		if (dp->dtdo_flags & DIFOFLG_DESTRUCTIVE &&
> -		    dest_ok == DTRACEOPT_UNSET)
> -			return dt_set_errno(dtp, EDT_DESTRUCTIVE);
> +		    dest_ok == DTRACEOPT_UNSET) {
> +			dt_set_errno(dtp, EDT_DESTRUCTIVE);
> +			goto fail;
> +		}
>   
>   		fd = dt_bpf_load_prog(dtp, prp, dp, cflags);
>   		if (fd == -1)
> -			return -1;
> +			goto fail;
>   
>   		if (prp->prov->impl->attach)
>   			rc = prp->prov->impl->attach(dtp, prp, fd);
>   
>   		if (rc < 0) {
>   			close(fd);
> -			return dt_attach_error(dtp, rc,
> -					       prp->desc->prv, prp->desc->mod,
> -					       prp->desc->fun, prp->desc->prb);
> +			dt_attach_error(dtp, rc,
> +					prp->desc->prv, prp->desc->mod,
> +					prp->desc->fun, prp->desc->prb);
> +			goto fail;
>   		}
> +
> +		dt_difo_free(dtp, prp->difo);
> +		prp->difo = NULL;
>   	}
>   
>   	return 0;
> +
> +fail:
> +	dt_difo_free(dtp, prp->difo);
> +	prp->difo = NULL;
> +	return -1;
>   }
> diff --git a/libdtrace/dt_prov_uprobe.c b/libdtrace/dt_prov_uprobe.c
> index f60bdceb..8e7aa4b0 100644
> --- a/libdtrace/dt_prov_uprobe.c
> +++ b/libdtrace/dt_prov_uprobe.c
> @@ -609,32 +609,40 @@ static int add_probe_uprobe(dtrace_hdl_t *dtp, dt_probe_t *prp)
>   	/* Make program. */
>   	dp = dt_construct(dtp, prp, cflags, NULL);
>   	if (dp == NULL)
> -		return 0;        // FIXME in dt_bpf_make_progs() this is a fatal error; should we do the same here?
> +		return 0;
>   	prp->difo = dp;
>   
>   	/* Load program. */
>   	if (dt_link(dtp, prp, dp, NULL) == -1)
> -		return 0;        // FIXME in dt_bpf_load_progs() this is a fatal error; should we do the same here?
> +		goto fail;
>   
>   	dtrace_getopt(dtp, "destructive", &dest_ok);
>   	if (dp->dtdo_flags & DIFOFLG_DESTRUCTIVE &&
> -	    dest_ok == DTRACEOPT_UNSET)
> -		return dt_set_errno(dtp, EDT_DESTRUCTIVE);
> +	    dest_ok == DTRACEOPT_UNSET) {
> +		dt_set_errno(dtp, EDT_DESTRUCTIVE);
> +		goto fail;
> +	}
>   
>   	fd = dt_bpf_load_prog(dtp, prp, dp, cflags);
>   	if (fd == -1)
> -		return 0;        // FIXME in dt_bpf_load_progs() this is a fatal error; should we do the same here?
> +		goto fail;
>   
>   	if (prp->prov->impl->attach)
>   		rc = prp->prov->impl->attach(dtp, prp, fd);
>   
>   	if (rc < 0) {
>   		close(fd);
> -		return dt_attach_error(dtp, rc, prp->desc->prv, prp->desc->mod,
> -						prp->desc->fun, prp->desc->prb);
> +		dt_attach_error(dtp, rc, prp->desc->prv, prp->desc->mod,
> +					 prp->desc->fun, prp->desc->prb);
> +		goto fail;
>   	}
>   
>   	return 0;
> +
> +fail:
> +	dt_difo_free(dtp, prp->difo);
> +	prp->difo = NULL;
> +	return 0;	// FIXME in dt_bpf_make_progs() this is a fatal error; should we do the same here?
>   }
>   
>   static int add_probe_usdt(dtrace_hdl_t *dtp, dt_probe_t *prp)