Hi,
On Wed, 17 Jun 2020 16:08:17 +0200
Sascha Ortmann <sascha.ortmann@xxxxxxxxxxxxxxxxxxxx> wrote:
> Fix boottime kprobe events to add multiple events even if one fails
> and report probe generation failures.
>
> As an example, when we try to set multiprobe kprobe events in
> bootconfig like this:
>
> ftrace.event.kprobes.vfsevents {
> probes = "vfs_read $arg1 $arg2,,
> !error! not reported;?", // leads to error
> "vfs_write $arg1 $arg2"
> }
>
> this will not work like expected. After commit
> da0f1f4167e3af69e1d8b32d6d65195ddd2bfb64 ("tracing/boottime:
> Fix kprobe event API usage"), the function
> trace_boot_add_kprobe_event will not produce any error message,
> aborting the function and stopping subsequent probes from getting
> installed when adding a probe fails at kprobe_event_gen_cmd_start.
Ah, good catch!
Indeed, I missed the error message.
> Furthermore, probes continue when kprobe_event_gen_cmd_end fails
> (and kprobe_event_gen_cmd_start did not fail). In this case the
> function even returns successfully when the last call to
> kprobe_event_gen_cmd_end is successful.
>
> The behaviour of reporting and aborting after failures is not
> consistent.
OK. And for more consistency, we should abort the loop if we hit any
error instead of continuing, because if trace_boot_add_kprobe_event()
returns an error code, the rest of event settings are skipped.
(See trace_boot_init_one_event())
>
> The function trace_boot_add_kprobe_event now continues even when
> one of the multiple events fails. Each failure is now reported
> individually. Since the function can only return one result to the
> caller, the function returns now the last failure (or none, if
> nothing fails).
>
> Cc: linux-kernel@xxxxxxxxxxxx
> Signed-off-by: Maximilian Werner <maximilian.werner96@xxxxxxxxx>
> Signed-off-by: Sascha Ortmann <sascha.ortmann@xxxxxxxxxxxxxxxxxxxx>
> ---
> kernel/trace/trace_boot.c | 16 +++++++++++-----
> 1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/trace/trace_boot.c b/kernel/trace/trace_boot.c
> index 9de29bb45a27..dbb50184e060 100644
> --- a/kernel/trace/trace_boot.c
> +++ b/kernel/trace/trace_boot.c
> @@ -95,18 +95,24 @@ trace_boot_add_kprobe_event(struct xbc_node *node, const char *event)
> struct xbc_node *anode;
> char buf[MAX_BUF_LEN];
> const char *val;
> + int error = 0;
> int ret = 0;
>
> xbc_node_for_each_array_value(node, "probes", anode, val) {
> kprobe_event_cmd_init(&cmd, buf, MAX_BUF_LEN);
>
> - ret = kprobe_event_gen_cmd_start(&cmd, event, val);
> - if (ret)
> - break;
> + error = kprobe_event_gen_cmd_start(&cmd, event, val);
> + if (error) {
> + pr_err("Failed to generate probe: %s\n", buf);
> + ret = error;
> + continue;
so, could you break here?
> + }
>
> - ret = kprobe_event_gen_cmd_end(&cmd);
> - if (ret)
> + error = kprobe_event_gen_cmd_end(&cmd);
> + if (error) {
> pr_err("Failed to add probe: %s\n", buf);
> + ret = error;
And here.
> + }
> }
>
> return ret;
> --
> 2.17.1
>
Thank you!
--
Masami Hiramatsu <mhiramat@xxxxxxxxxx>
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