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Subject[PATCH] tracepoints: Code clean up
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
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 */

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;
+ 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 */
+ }
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);
+ }
*funcs = old;
}
}
--
2.25.4
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