[PATCH v3 00/27] function_graph: Allow multiple users for function graph tracing

Steven Rostedt
2024-06-03T19:07:10Z

This is a continuation of the function graph multi user code.
I wrote a proof of concept back in 2019 of this code[1] and
Masami started cleaning it up. I started from Masami's work v10
that can be found here:

https://lore.kernel.org/linux-trace-kernel/171509088006.162236.7227326999861366050.stgit@devnote2/

This is *only* the code that allows multiple users of function
graph tracing. This is not the fprobe work that Masami is working
to add on top of it. As Masami took my proof of concept, there
was still several things I disliked about that code. Instead of
having Masami clean it up even more, I decided to take over on just
my code and change it up a bit.

Changes since v2: https://lore.kernel.org/linux-trace-kernel/20240602033744.563858532@goodmis.org

- Added comments describing which hashes the append and intersect
functions were used for.

- Replaced checks of (NULL or EMPTY_HASH) with ftrace_hash_empty()
helper function.

- Added check at the end of intersect_hash() to convert the hash
to EMPTY hash if it doesn't have any functions.

- Renamed compare_ops() to ops_equal() and return boolean (inversed return
value).

- Broke out __ftrace_hash_move_and_update_ops() to use in both
ftrace_hash_move_and_update_ops() and ftrace_hash_move_and_update_subops().

Diff between last version at end of this email.

Masami Hiramatsu (Google) (3):
function_graph: Handle tail calls for stack unwinding
function_graph: Use a simple LRU for fgraph_array index number
ftrace: Add multiple fgraph storage selftest

Steven Rostedt (Google) (9):
ftrace: Add subops logic to allow one ops to manage many
ftrace: Allow subops filtering to be modified
function_graph: Add pid tracing back to function graph tracer
function_graph: Use for_each_set_bit() in __ftrace_return_to_handler()
function_graph: Use bitmask to loop on fgraph entry
function_graph: Use static_call and branch to optimize entry function
function_graph: Use static_call and branch to optimize return function
selftests/ftrace: Add function_graph tracer to func-filter-pid test
selftests/ftrace: Add fgraph-multi.tc test

Steven Rostedt (VMware) (15):
function_graph: Convert ret_stack to a series of longs
fgraph: Use BUILD_BUG_ON() to make sure we have structures divisible by long
function_graph: Add an array structure that will allow multiple callbacks
function_graph: Allow multiple users to attach to function graph
function_graph: Remove logic around ftrace_graph_entry and return
ftrace/function_graph: Pass fgraph_ops to function graph callbacks
ftrace: Allow function_graph tracer to be enabled in instances
ftrace: Allow ftrace startup flags to exist without dynamic ftrace
function_graph: Have the instances use their own ftrace_ops for filtering
function_graph: Add "task variables" per task for fgraph_ops
function_graph: Move set_graph_function tests to shadow stack global var
function_graph: Move graph depth stored data to shadow stack global var
function_graph: Move graph notrace bit to shadow stack global var
function_graph: Implement fgraph_reserve_data() and fgraph_retrieve_data()
function_graph: Add selftest for passing local variables

----
include/linux/ftrace.h | 43 +-
include/linux/sched.h | 2 +-
include/linux/trace_recursion.h | 39 -
kernel/trace/fgraph.c | 1044 ++++++++++++++++----
kernel/trace/ftrace.c | 522 +++++++++-
kernel/trace/ftrace_internal.h | 5 +-
kernel/trace/trace.h | 94 +-
kernel/trace/trace_functions.c | 8 +
kernel/trace/trace_functions_graph.c | 96 +-
kernel/trace/trace_irqsoff.c | 10 +-
kernel/trace/trace_sched_wakeup.c | 10 +-
kernel/trace/trace_selftest.c | 259 ++++-
.../selftests/ftrace/test.d/ftrace/fgraph-multi.tc | 103 ++
.../ftrace/test.d/ftrace/func-filter-pid.tc | 27 +-
14 files changed, 1945 insertions(+), 317 deletions(-)
create mode 100644 tools/testing/selftests/ftrace/test.d/ftrace/fgraph-multi.tc

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 41fabc6d30e4..da7e6abf48b4 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3170,7 +3170,7 @@ int ftrace_shutdown(struct ftrace_ops *ops, int command)
/* Simply make a copy of @src and return it */
static struct ftrace_hash *copy_hash(struct ftrace_hash *src)
{
- if (!src || src == EMPTY_HASH)
+ if (ftrace_hash_empty(src))
return EMPTY_HASH;

return alloc_and_copy_ftrace_hash(src->size_bits, src);
@@ -3187,6 +3187,9 @@ static struct ftrace_hash *copy_hash(struct ftrace_hash *src)
*
* Otherwise, go through all of @new_hash and add anything that @hash
* doesn't already have, to @hash.
+ *
+ * The filter_hash updates uses just the append_hash() function
+ * and the notrace_hash does not.
*/
static int append_hash(struct ftrace_hash **hash, struct ftrace_hash *new_hash)
{
@@ -3195,11 +3198,11 @@ static int append_hash(struct ftrace_hash **hash, struct ftrace_hash *new_hash)
int i;

/* An empty hash does everything */
- if (!*hash || *hash == EMPTY_HASH)
+ if (ftrace_hash_empty(*hash))
return 0;

/* If new_hash has everything make hash have everything */
- if (!new_hash || new_hash == EMPTY_HASH) {
+ if (ftrace_hash_empty(new_hash)) {
free_ftrace_hash(*hash);
*hash = EMPTY_HASH;
return 0;
@@ -3217,7 +3220,12 @@ static int append_hash(struct ftrace_hash **hash, struct ftrace_hash *new_hash)
return 0;
}

-/* Add to @hash only those that are in both @new_hash1 and @new_hash2 */
+/*
+ * Add to @hash only those that are in both @new_hash1 and @new_hash2
+ *
+ * The notrace_hash updates uses just the intersect_hash() function
+ * and the filter_hash does not.
+ */
static int intersect_hash(struct ftrace_hash **hash, struct ftrace_hash *new_hash1,
struct ftrace_hash *new_hash2)
{
@@ -3229,8 +3237,7 @@ static int intersect_hash(struct ftrace_hash **hash, struct ftrace_hash *new_has
* If new_hash1 or new_hash2 is the EMPTY_HASH then make the hash
* empty as well as empty for notrace means none are notraced.
*/
- if (!new_hash1 || new_hash1 == EMPTY_HASH ||
- !new_hash2 || new_hash2 == EMPTY_HASH) {
+ if (ftrace_hash_empty(new_hash1) || ftrace_hash_empty(new_hash2)) {
free_ftrace_hash(*hash);
*hash = EMPTY_HASH;
return 0;
@@ -3245,6 +3252,11 @@ static int intersect_hash(struct ftrace_hash **hash, struct ftrace_hash *new_has
return -ENOMEM;
}
}
+ /* If nothing intersects, make it the empty set */
+ if (ftrace_hash_empty(*hash)) {
+ free_ftrace_hash(*hash);
+ *hash = EMPTY_HASH;
+ }
return 0;
}

@@ -3266,7 +3278,7 @@ static struct ftrace_hash *append_hashes(struct ftrace_ops *ops)
return NULL;
}
/* Nothing more to do if new_hash is empty */
- if (new_hash == EMPTY_HASH)
+ if (ftrace_hash_empty(new_hash))
break;
}
return new_hash;
@@ -3300,59 +3312,76 @@ static struct ftrace_hash *intersect_hashes(struct ftrace_ops *ops)
return NULL;
}
/* Nothing more to do if new_hash is empty */
- if (new_hash == EMPTY_HASH)
+ if (ftrace_hash_empty(new_hash))
break;
}
return new_hash;
}

-/* Returns 0 on equal or non-zero on non-equal */
-static int compare_ops(struct ftrace_hash *A, struct ftrace_hash *B)
+static bool ops_equal(struct ftrace_hash *A, struct ftrace_hash *B)
{
struct ftrace_func_entry *entry;
int size;
int i;

- if (!A || A == EMPTY_HASH)
- return !(!B || B == EMPTY_HASH);
+ if (ftrace_hash_empty(A))
+ return ftrace_hash_empty(B);

- if (!B || B == EMPTY_HASH)
- return !(!A || A == EMPTY_HASH);
+ if (ftrace_hash_empty(B))
+ return ftrace_hash_empty(A);

if (A->count != B->count)
- return 1;
+ return false;

size = 1 << A->size_bits;
for (i = 0; i < size; i++) {
hlist_for_each_entry(entry, &A->buckets[i], hlist) {
if (!__ftrace_lookup_ip(B, entry->ip))
- return 1;
+ return false;
}
}

- return 0;
+ return true;
}

-static int ftrace_hash_move_and_update_ops(struct ftrace_ops *ops,
- struct ftrace_hash **orig_hash,
- struct ftrace_hash *hash,
- int enable);
+static void ftrace_ops_update_code(struct ftrace_ops *ops,
+ struct ftrace_ops_hash *old_hash);
+
+static int __ftrace_hash_move_and_update_ops(struct ftrace_ops *ops,
+ struct ftrace_hash **orig_hash,
+ struct ftrace_hash *hash,
+ int enable)
+{
+ struct ftrace_ops_hash old_hash_ops;
+ struct ftrace_hash *old_hash;
+ int ret;
+
+ old_hash = *orig_hash;
+ old_hash_ops.filter_hash = ops->func_hash->filter_hash;
+ old_hash_ops.notrace_hash = ops->func_hash->notrace_hash;
+ ret = ftrace_hash_move(ops, enable, orig_hash, hash);
+ if (!ret) {
+ ftrace_ops_update_code(ops, &old_hash_ops);
+ free_ftrace_hash_rcu(old_hash);
+ }
+ return ret;
+}

static int ftrace_update_ops(struct ftrace_ops *ops, struct ftrace_hash *filter_hash,
struct ftrace_hash *notrace_hash)
{
int ret;

- if (compare_ops(filter_hash, ops->func_hash->filter_hash)) {
- ret = ftrace_hash_move_and_update_ops(ops, &ops->func_hash->filter_hash,
- filter_hash, 1);
+ if (!ops_equal(filter_hash, ops->func_hash->filter_hash)) {
+ ret = __ftrace_hash_move_and_update_ops(ops, &ops->func_hash->filter_hash,
+ filter_hash, 1);
if (ret < 0)
return ret;
}

- if (compare_ops(notrace_hash, ops->func_hash->notrace_hash)) {
- ret = ftrace_hash_move_and_update_ops(ops, &ops->func_hash->notrace_hash,
- notrace_hash, 0);
+ if (!ops_equal(notrace_hash, ops->func_hash->notrace_hash)) {
+ ret = __ftrace_hash_move_and_update_ops(ops, &ops->func_hash->notrace_hash,
+ notrace_hash, 0);
if (ret < 0)
return ret;
}
@@ -3438,8 +3467,8 @@ int ftrace_startup_subops(struct ftrace_ops *ops, struct ftrace_ops *subops, int
* o If either notrace_hash is empty then the final stays empty
* o Otherwise, the final is an intersection between the hashes
*/
- if (ops->func_hash->filter_hash == EMPTY_HASH ||
- subops->func_hash->filter_hash == EMPTY_HASH) {
+ if (ftrace_hash_empty(ops->func_hash->filter_hash) ||
+ ftrace_hash_empty(subops->func_hash->filter_hash)) {
filter_hash = EMPTY_HASH;
} else {
size_bits = max(ops->func_hash->filter_hash->size_bits,
@@ -3454,8 +3483,8 @@ int ftrace_startup_subops(struct ftrace_ops *ops, struct ftrace_ops *subops, int
}
}

- if (ops->func_hash->notrace_hash == EMPTY_HASH ||
- subops->func_hash->notrace_hash == EMPTY_HASH) {
+ if (ftrace_hash_empty(ops->func_hash->notrace_hash) ||
+ ftrace_hash_empty(subops->func_hash->notrace_hash)) {
notrace_hash = EMPTY_HASH;
} else {
size_bits = max(ops->func_hash->filter_hash->size_bits,
@@ -3591,7 +3620,7 @@ static int ftrace_hash_move_and_update_subops(struct ftrace_ops *subops,
}

/* Move the hash over to the new hash */
- ret = ftrace_hash_move_and_update_ops(ops, orig_hash, new_hash, enable);
+ ret = __ftrace_hash_move_and_update_ops(ops, orig_hash, new_hash, enable);

free_ftrace_hash(new_hash);

@@ -4822,11 +4851,6 @@ static int ftrace_hash_move_and_update_ops(struct ftrace_ops *ops,
struct ftrace_hash *hash,
int enable)
{
- struct ftrace_ops_hash old_hash_ops;
- struct ftrace_hash *old_hash;
- struct ftrace_ops *op;
- int ret;
-
if (ops->flags & FTRACE_OPS_FL_SUBOP)
return ftrace_hash_move_and_update_subops(ops, orig_hash, hash, enable);

@@ -4838,6 +4862,8 @@ static int ftrace_hash_move_and_update_ops(struct ftrace_ops *ops,
* it will not affect subops that share it.
*/
if (!(ops->flags & FTRACE_OPS_FL_ENABLED)) {
+ struct ftrace_ops *op;
+
/* Check if any other manager subops maps to this hash */
do_for_each_ftrace_op(op, ftrace_ops_list) {
struct ftrace_ops *subops;
@@ -4851,15 +4877,7 @@ static int ftrace_hash_move_and_update_ops(struct ftrace_ops *ops,
} while_for_each_ftrace_op(op);
}

- old_hash = *orig_hash;
- old_hash_ops.filter_hash = ops->func_hash->filter_hash;
- old_hash_ops.notrace_hash = ops->func_hash->notrace_hash;
- ret = ftrace_hash_move(ops, enable, orig_hash, hash);
- if (!ret) {
- ftrace_ops_update_code(ops, &old_hash_ops);
- free_ftrace_hash_rcu(old_hash);
- }
- return ret;
+ return __ftrace_hash_move_and_update_ops(ops, orig_hash, hash, enable);
}

static bool module_exists(const char *module)