Chuang W wrote:
> Before the 0bc11ed5ab60 commit ("kprobes: Allow kprobes coexist with
> livepatch"), in a scenario where livepatch and kprobe coexist on the
> same function entry, the creation of kprobe_event using
> add_kprobe_event_legacy() will be successful, at the same time as a
> trace event (e.g. /debugfs/tracing/events/kprobe/XX) will exist, but
> perf_event_open() will return an error because both livepatch and kprobe
> use FTRACE_OPS_FL_IPMODIFY.
>
> With this patch, whenever an error is returned after
> add_kprobe_event_legacy(), this ensures that the created kprobe_event is
> cleaned.
>
> Signed-off-by: Chuang W <nashuiliang@xxxxxxxxx>
> Signed-off-by: Jingren Zhou <zhoujingren@xxxxxxxxxxxxxx>
> ---
> tools/lib/bpf/libbpf.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
I think we want to improve the commit message otherwise I'm sure we will
stumble on this in the future and from just above its tricky to follow.
I would suggest almost verbatim the description you gave in reply to
my question. Just cut'n'pasting your text together with minor edit
glue,
"
The legacy kprobe API (i.e. tracefs API) has two steps:
1) register_kprobe
$ echo 'p:mykprobe XXX' > /sys/kernel/debug/tracing/kprobe_events
This will create a trace event of mykprobe and register a disable
kprobe that waits to be activated.
2) enable_kprobe
2.1) using syscall perf_event_open as the following code,
perf_event_kprobe_open_legacy (file: tools/lib/bpf/libbpf.c):
---
attr.type = PERF_TYPE_TRACEPOINT;
pfd = syscall(__NR_perf_event_open, &attr,
pid < 0 ? -1 : pid, /* pid */
pid == -1 ? 0 : -1, /* cpu */
-1 /* group_fd */, PERF_FLAG_FD_CLOEXEC);
---
In the implementation code of perf_event_open, enable_kprobe() will be executed.
2.2) using shell
$ echo 1 > /sys/kernel/debug/tracing/events/kprobes/mykprobe/enable
As with perf_event_open, enable_kprobe() will also be executed.
When using the same function XXX, kprobe and livepatch cannot coexist,
that is, step 2) will return an error (ref: arm_kprobe_ftrace()),
however, step 1) is ok! The new kprobe API (i.e. perf kprobe API)
aggregates register_kprobe and enable_kprobe, internally fixes the
issue on failed enable_kprobe.
To fix: before the 0bc11ed5ab60 commit ("kprobes: Allow kprobes coexist with
livepatch"), in a scenario where livepatch and kprobe coexist on the
same function entry, the creation of kprobe_event using
add_kprobe_event_legacy() will be successful, at the same time as a
trace event (e.g. /debugfs/tracing/events/kprobe/XX) will exist, but
perf_event_open() will return an error because both livepatch and kprobe
use FTRACE_OPS_FL_IPMODIFY.
With this patch, whenever an error is returned after
add_kprobe_event_legacy(), this ensures that the created kprobe_event is
cleaned.
"
Thanks,
John
