Commit 7211f0a2 authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware)
Browse files

tracepoints: Code clean up 

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 load/store
tearing to the 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.

Link: https://lkml.kernel.org/r/20210204143004.61126582@gandalf.local.home



Signed-off-by: default avatarMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent d9a1be1b

include/linux/tracepoint.h

+1 −1
Original line number Diff line number Diff line
@@ -305,7 +305,7 @@ 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);		\

kernel/tracepoint.c

+35 −56
Original line number Diff line number Diff line
@@ -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;		/* Insertion position into new array */



	if (WARN_ON(!tp_func->func))

		return ERR_PTR(-EINVAL);
@@ -147,54 +147,38 @@ 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)

		nr_probes = 0;

		for (iter_probes = 0; old[iter_probes].func; iter_probes++) {

			if (old[iter_probes].func == tp_stub_func)

				continue;

				if (pos < 0 && old[nr_probes].prio < prio)

					pos = probes++;

				new[probes++] = old[nr_probes];

			/* Insert before probes of lower priority */

			if (pos < 0 && old[iter_probes].prio < prio)

				pos = nr_probes++;

			new[nr_probes++] = old[iter_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));

			pos = nr_probes++;

		/* nr_probes now points to the end of the new array */

	} 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));

		}

	} 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 +221,12 @@ 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 {
@@ -249,16 +234,10 @@ 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;

		}