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SubjectRe: [PATCH] tracepoints: Code clean up
----- On Feb 4, 2021, at 1:27 PM, rostedt rostedt@goodmis.org wrote:

> From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
>
> Restructure the code a bit to make it simpler, fix some formatting problems
> and add READ_ONCE/WRITE_ONCE to make sure there's no compiler tear downs on

compiler tear downs -> compiler load/store tearing.

> changes to variables that can be accessed across CPUs.
>
> Started with Mathieu Desnoyers's patch:
>
> Link:
> https://lore.kernel.org/lkml/20210203175741.20665-1-mathieu.desnoyers@efficios.com/
>
> And will keep his signature, but I will take the responsibility of this
> being correct, and keep the authorship.
>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> ---
> include/linux/tracepoint.h | 2 +-
> kernel/tracepoint.c | 92 +++++++++++++++-----------------------
> 2 files changed, 37 insertions(+), 57 deletions(-)
>
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 966ed8980327..dc1d4c612cc3 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -309,7 +309,7 @@ static inline struct tracepoint
> *tracepoint_ptr_deref(tracepoint_ptr_t *p)
> rcu_dereference_raw((&__tracepoint_##_name)->funcs); \
> if (it_func_ptr) { \
> do { \
> - it_func = (it_func_ptr)->func; \
> + it_func = READ_ONCE((it_func_ptr)->func); \
> __data = (it_func_ptr)->data; \
> ((void(*)(void *, proto))(it_func))(__data, args); \
> } while ((++it_func_ptr)->func); \
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index e8f20ae29c18..4b9de79bb927 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c
> @@ -136,9 +136,9 @@ func_add(struct tracepoint_func **funcs, struct
> tracepoint_func *tp_func,
> int prio)
> {
> struct tracepoint_func *old, *new;
> - int nr_probes = 0;
> - int stub_funcs = 0;
> - int pos = -1;
> + int iter_probes; /* Iterate over old probe array. */
> + int nr_probes = 0; /* Counter for probes */
> + int pos = -1; /* New position */

New position -> Insertion position into new array

>
> if (WARN_ON(!tp_func->func))
> return ERR_PTR(-EINVAL);
> @@ -147,54 +147,39 @@ func_add(struct tracepoint_func **funcs, struct
> tracepoint_func *tp_func,
> old = *funcs;
> if (old) {
> /* (N -> N+1), (N != 0, 1) probes */
> - for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
> - /* Insert before probes of lower priority */
> - if (pos < 0 && old[nr_probes].prio < prio)
> - pos = nr_probes;
> - if (old[nr_probes].func == tp_func->func &&
> - old[nr_probes].data == tp_func->data)
> + for (iter_probes = 0; old[iter_probes].func; iter_probes++) {
> + if (old[iter_probes].func == tp_stub_func)
> + continue; /* Skip stub functions. */
> + if (old[iter_probes].func == tp_func->func &&
> + old[iter_probes].data == tp_func->data)
> return ERR_PTR(-EEXIST);
> - if (old[nr_probes].func == tp_stub_func)
> - stub_funcs++;
> + nr_probes++;
> }
> }
> - /* + 2 : one for new probe, one for NULL func - stub functions */
> - new = allocate_probes(nr_probes + 2 - stub_funcs);
> + /* + 2 : one for new probe, one for NULL func */
> + new = allocate_probes(nr_probes + 2);
> if (new == NULL)
> return ERR_PTR(-ENOMEM);
> if (old) {
> - if (stub_funcs) {
> - /* Need to copy one at a time to remove stubs */
> - int probes = 0;
> -
> - pos = -1;
> - for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
> - if (old[nr_probes].func == tp_stub_func)
> - continue;
> - if (pos < 0 && old[nr_probes].prio < prio)
> - pos = probes++;
> - new[probes++] = old[nr_probes];
> - }
> - nr_probes = probes;
> - if (pos < 0)
> - pos = probes;
> - else
> - nr_probes--; /* Account for insertion */
> -
> - } else if (pos < 0) {
> - pos = nr_probes;
> - memcpy(new, old, nr_probes * sizeof(struct tracepoint_func));
> - } else {
> - /* Copy higher priority probes ahead of the new probe */
> - memcpy(new, old, pos * sizeof(struct tracepoint_func));
> - /* Copy the rest after it. */
> - memcpy(new + pos + 1, old + pos,
> - (nr_probes - pos) * sizeof(struct tracepoint_func));
> + pos = -1;

pos is already initialized to -1 at function beginning.

> + nr_probes = 0;
> + for (iter_probes = 0; old[iter_probes].func; iter_probes++) {
> + if (old[iter_probes].func == tp_stub_func)
> + continue;
> + /* Insert before probes of lower priority */
> + if (pos < 0 && old[iter_probes].prio < prio)
> + pos = nr_probes++;
> + new[nr_probes++] = old[iter_probes];
> }
> - } else
> + if (pos < 0)
> + pos = nr_probes++;
> + /* nr_probes now points to the end of the new array */
> + } else {
> pos = 0;
> + nr_probes = 1; /* must point at end of array */

Yep, much nicer.

> + }
> new[pos] = *tp_func;
> - new[nr_probes + 1].func = NULL;
> + new[nr_probes].func = NULL;
> *funcs = new;
> debug_print_probes(*funcs);
> return old;
> @@ -237,11 +222,12 @@ static void *func_remove(struct tracepoint_func **funcs,
> /* + 1 for NULL */
> new = allocate_probes(nr_probes - nr_del + 1);
> if (new) {
> - for (i = 0; old[i].func; i++)
> - if ((old[i].func != tp_func->func
> - || old[i].data != tp_func->data)
> - && old[i].func != tp_stub_func)
> + for (i = 0; old[i].func; i++) {
> + if ((old[i].func != tp_func->func ||
> + old[i].data != tp_func->data) &&
> + old[i].func != tp_stub_func)
> new[j++] = old[i];
> + }
> new[nr_probes - nr_del].func = NULL;
> *funcs = new;
> } else {
> @@ -249,17 +235,11 @@ static void *func_remove(struct tracepoint_func **funcs,
> * Failed to allocate, replace the old function
> * with calls to tp_stub_func.
> */
> - for (i = 0; old[i].func; i++)
> + for (i = 0; old[i].func; i++) {
> if (old[i].func == tp_func->func &&
> - old[i].data == tp_func->data) {
> - old[i].func = tp_stub_func;
> - /* Set the prio to the next event. */
> - if (old[i + 1].func)
> - old[i].prio =
> - old[i + 1].prio;
> - else
> - old[i].prio = -1;
> - }
> + old[i].data == tp_func->data)
> + WRITE_ONCE(old[i].func, tp_stub_func);
> + }

The rest looks good, thanks!

You can keep my signed-off-by, and if needed may add my reviewed-by tag
as well. ;-)

Mathieu


> *funcs = old;
> }
> }
> --
> 2.25.4

--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

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