[PATCH bpf-next v4] bpf: Refactor active lock management

[PATCH bpf-next v4] bpf: Refactor active lock management

[Kumar Kartikeya Dwivedi]

When bpf_spin_lock was introduced originally, there was deliberation on
whether to use an array of lock IDs, but since bpf_spin_lock is limited
to holding a single lock at any given time, we've been using a single ID
to identify the held lock.

In preparation for introducing spin locks that can be taken multiple
times, introduce support for acquiring multiple lock IDs. For this
purpose, reuse the acquired_refs array and store both lock and pointer
references. We tag the entry with REF_TYPE_PTR or REF_TYPE_LOCK to
disambiguate and find the relevant entry. The ptr field is used to track
the map_ptr or btf (for bpf_obj_new allocations) to ensure locks can be
matched with protected fields within the same "allocation", i.e.
bpf_obj_new object or map value.

The struct active_lock is changed to an int as the state is part of the
acquired_refs array, and we only need active_lock as a cheap way of
detecting lock presence.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
Changelog:
v3 -> v4
v3: https://lore.kernel.org/bpf/20241104151716.2079893-1-memxor@gmail.com

 * Address comments from Alexei
   * Drop struct bpf_active_lock definition
   * Name enum type, expand definition to multiple lines
   * s/REF_TYPE_BPF_LOCK/REF_TYPE_LOCK/g
   * Change active_lock type to int
   * Fix type of 'type' in acquire_lock_state
   * Filter by taking type explicitly in find_lock_state
   * WARN for default case in refsafe switch statement

v2 -> v3
v2: https://lore.kernel.org/bpf/20241103212252.547071-1-memxor@gmail.com

  * Rebase on bpf-next to resolve merge conflict

v1 -> v2
v1: https://lore.kernel.org/bpf/20241103205856.345580-1-memxor@gmail.com

  * Fix refsafe state comparison to check callback_ref and ptr separately.
---
 include/linux/bpf_verifier.h |  53 ++++++-------
 kernel/bpf/verifier.c        | 143 ++++++++++++++++++++++++++---------
 2 files changed, 134 insertions(+), 62 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 4513372c5bc8..b248850396ac 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -48,22 +48,6 @@ enum bpf_reg_liveness {
 	REG_LIVE_DONE = 0x8, /* liveness won't be updating this register anymore */
 };

-/* For every reg representing a map value or allocated object pointer,
- * we consider the tuple of (ptr, id) for them to be unique in verifier
- * context and conside them to not alias each other for the purposes of
- * tracking lock state.
- */
-struct bpf_active_lock {
-	/* This can either be reg->map_ptr or reg->btf. If ptr is NULL,
-	 * there's no active lock held, and other fields have no
-	 * meaning. If non-NULL, it indicates that a lock is held and
-	 * id member has the reg->id of the register which can be >= 0.
-	 */
-	void *ptr;
-	/* This will be reg->id */
-	u32 id;
-};
-
 #define ITER_PREFIX "bpf_iter_"

 enum bpf_iter_state {
@@ -266,6 +250,13 @@ struct bpf_stack_state {
 };

 struct bpf_reference_state {
+	/* Each reference object has a type. Ensure REF_TYPE_PTR is zero to
+	 * default to pointer reference on zero initialization of a state.
+	 */
+	enum ref_state_type {
+		REF_TYPE_PTR = 0,
+		REF_TYPE_LOCK,
+	} type;
 	/* Track each reference created with a unique id, even if the same
 	 * instruction creates the reference multiple times (eg, via CALL).
 	 */
@@ -274,17 +265,23 @@ struct bpf_reference_state {
 	 * is used purely to inform the user of a reference leak.
 	 */
 	int insn_idx;
-	/* There can be a case like:
-	 * main (frame 0)
-	 *  cb (frame 1)
-	 *   func (frame 3)
-	 *    cb (frame 4)
-	 * Hence for frame 4, if callback_ref just stored boolean, it would be
-	 * impossible to distinguish nested callback refs. Hence store the
-	 * frameno and compare that to callback_ref in check_reference_leak when
-	 * exiting a callback function.
-	 */
-	int callback_ref;
+	union {
+		/* There can be a case like:
+		 * main (frame 0)
+		 *  cb (frame 1)
+		 *   func (frame 3)
+		 *    cb (frame 4)
+		 * Hence for frame 4, if callback_ref just stored boolean, it would be
+		 * impossible to distinguish nested callback refs. Hence store the
+		 * frameno and compare that to callback_ref in check_reference_leak when
+		 * exiting a callback function.
+		 */
+		int callback_ref;
+		/* Use to keep track of the source object of a lock, to ensure
+		 * it matches on unlock.
+		 */
+		void *ptr;
+	};
 };

 struct bpf_retval_range {
@@ -434,7 +431,7 @@ struct bpf_verifier_state {
 	u32 insn_idx;
 	u32 curframe;

-	struct bpf_active_lock active_lock;
+	int active_lock;
 	bool speculative;
 	bool active_rcu_lock;
 	u32 active_preempt_lock;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 132fc172961f..e04be1241a2c 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1354,6 +1354,7 @@ static int acquire_reference_state(struct bpf_verifier_env *env, int insn_idx)
 	if (err)
 		return err;
 	id = ++env->id_gen;
+	state->refs[new_ofs].type = REF_TYPE_PTR;
 	state->refs[new_ofs].id = id;
 	state->refs[new_ofs].insn_idx = insn_idx;
 	state->refs[new_ofs].callback_ref = state->in_callback_fn ? state->frameno : 0;
@@ -1361,6 +1362,24 @@ static int acquire_reference_state(struct bpf_verifier_env *env, int insn_idx)
 	return id;
 }

+static int acquire_lock_state(struct bpf_verifier_env *env, int insn_idx, enum ref_state_type type,
+			      int id, void *ptr)
+{
+	struct bpf_func_state *state = cur_func(env);
+	int new_ofs = state->acquired_refs;
+	int err;
+
+	err = resize_reference_state(state, state->acquired_refs + 1);
+	if (err)
+		return err;
+	state->refs[new_ofs].type = type;
+	state->refs[new_ofs].id = id;
+	state->refs[new_ofs].insn_idx = insn_idx;
+	state->refs[new_ofs].ptr = ptr;
+
+	return 0;
+}
+
 /* release function corresponding to acquire_reference_state(). Idempotent. */
 static int release_reference_state(struct bpf_func_state *state, int ptr_id)
 {
@@ -1368,6 +1387,8 @@ static int release_reference_state(struct bpf_func_state *state, int ptr_id)

 	last_idx = state->acquired_refs - 1;
 	for (i = 0; i < state->acquired_refs; i++) {
+		if (state->refs[i].type != REF_TYPE_PTR)
+			continue;
 		if (state->refs[i].id == ptr_id) {
 			/* Cannot release caller references in callbacks */
 			if (state->in_callback_fn && state->refs[i].callback_ref != state->frameno)
@@ -1383,6 +1404,44 @@ static int release_reference_state(struct bpf_func_state *state, int ptr_id)
 	return -EINVAL;
 }

+static int release_lock_state(struct bpf_func_state *state, int type, int id, void *ptr)
+{
+	int i, last_idx;
+
+	last_idx = state->acquired_refs - 1;
+	for (i = 0; i < state->acquired_refs; i++) {
+		if (state->refs[i].type != type)
+			continue;
+		if (state->refs[i].id == id && state->refs[i].ptr == ptr) {
+			if (last_idx && i != last_idx)
+				memcpy(&state->refs[i], &state->refs[last_idx],
+				       sizeof(*state->refs));
+			memset(&state->refs[last_idx], 0, sizeof(*state->refs));
+			state->acquired_refs--;
+			return 0;
+		}
+	}
+	return -EINVAL;
+}
+
+static struct bpf_reference_state *find_lock_state(struct bpf_verifier_env *env, enum ref_state_type type,
+						   int id, void *ptr)
+{
+	struct bpf_func_state *state = cur_func(env);
+	int i;
+
+	for (i = 0; i < state->acquired_refs; i++) {
+		struct bpf_reference_state *s = &state->refs[i];
+
+		if (s->type == REF_TYPE_PTR || s->type != type)
+			continue;
+
+		if (s->id == id && s->ptr == ptr)
+			return s;
+	}
+	return NULL;
+}
+
 static void free_func_state(struct bpf_func_state *state)
 {
 	if (!state)
@@ -1449,12 +1508,11 @@ static int copy_verifier_state(struct bpf_verifier_state *dst_state,
 		dst_state->frame[i] = NULL;
 	}
 	dst_state->speculative = src->speculative;
+	dst_state->active_lock = src->active_lock;
 	dst_state->active_rcu_lock = src->active_rcu_lock;
 	dst_state->active_preempt_lock = src->active_preempt_lock;
 	dst_state->in_sleepable = src->in_sleepable;
 	dst_state->curframe = src->curframe;
-	dst_state->active_lock.ptr = src->active_lock.ptr;
-	dst_state->active_lock.id = src->active_lock.id;
 	dst_state->branches = src->branches;
 	dst_state->parent = src->parent;
 	dst_state->first_insn_idx = src->first_insn_idx;
@@ -5442,7 +5500,7 @@ static bool in_sleepable(struct bpf_verifier_env *env)
 static bool in_rcu_cs(struct bpf_verifier_env *env)
 {
 	return env->cur_state->active_rcu_lock ||
-	       env->cur_state->active_lock.ptr ||
+	       env->cur_state->active_lock ||
 	       !in_sleepable(env);
 }

@@ -7737,6 +7795,7 @@ static int process_spin_lock(struct bpf_verifier_env *env, int regno,
 	struct bpf_map *map = NULL;
 	struct btf *btf = NULL;
 	struct btf_record *rec;
+	int err;

 	if (!is_const) {
 		verbose(env,
@@ -7768,16 +7827,27 @@ static int process_spin_lock(struct bpf_verifier_env *env, int regno,
 		return -EINVAL;
 	}
 	if (is_lock) {
-		if (cur->active_lock.ptr) {
+		void *ptr;
+
+		if (map)
+			ptr = map;
+		else
+			ptr = btf;
+
+		if (cur->active_lock) {
 			verbose(env,
 				"Locking two bpf_spin_locks are not allowed\n");
 			return -EINVAL;
 		}
-		if (map)
-			cur->active_lock.ptr = map;
-		else
-			cur->active_lock.ptr = btf;
-		cur->active_lock.id = reg->id;
+		err = acquire_lock_state(env, env->insn_idx, REF_TYPE_LOCK, reg->id, ptr);
+		if (err < 0) {
+			verbose(env, "Failed to acquire lock state\n");
+			return err;
+		}
+		/* It is not safe to allow multiple bpf_spin_lock calls, so
+		 * disallow them until this lock has been unlocked.
+		 */
+		cur->active_lock++;
 	} else {
 		void *ptr;

@@ -7786,20 +7856,18 @@ static int process_spin_lock(struct bpf_verifier_env *env, int regno,
 		else
 			ptr = btf;

-		if (!cur->active_lock.ptr) {
+		if (!cur->active_lock) {
 			verbose(env, "bpf_spin_unlock without taking a lock\n");
 			return -EINVAL;
 		}
-		if (cur->active_lock.ptr != ptr ||
-		    cur->active_lock.id != reg->id) {
+
+		if (release_lock_state(cur_func(env), REF_TYPE_LOCK, reg->id, ptr)) {
 			verbose(env, "bpf_spin_unlock of different lock\n");
 			return -EINVAL;
 		}

 		invalidate_non_owning_refs(env);
-
-		cur->active_lock.ptr = NULL;
-		cur->active_lock.id = 0;
+		cur->active_lock--;
 	}
 	return 0;
 }
@@ -9861,7 +9929,7 @@ static int check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 		const char *sub_name = subprog_name(env, subprog);

 		/* Only global subprogs cannot be called with a lock held. */
-		if (env->cur_state->active_lock.ptr) {
+		if (env->cur_state->active_lock) {
 			verbose(env, "global function calls are not allowed while holding a lock,\n"
 				     "use static function instead\n");
 			return -EINVAL;
@@ -10386,6 +10454,8 @@ static int check_reference_leak(struct bpf_verifier_env *env, bool exception_exi
 		return 0;

 	for (i = 0; i < state->acquired_refs; i++) {
+		if (state->refs[i].type != REF_TYPE_PTR)
+			continue;
 		if (!exception_exit && state->in_callback_fn && state->refs[i].callback_ref != state->frameno)
 			continue;
 		verbose(env, "Unreleased reference id=%d alloc_insn=%d\n",
@@ -10399,7 +10469,7 @@ static int check_resource_leak(struct bpf_verifier_env *env, bool exception_exit
 {
 	int err;

-	if (check_lock && env->cur_state->active_lock.ptr) {
+	if (check_lock && env->cur_state->active_lock) {
 		verbose(env, "%s cannot be used inside bpf_spin_lock-ed region\n", prefix);
 		return -EINVAL;
 	}
@@ -11623,7 +11693,7 @@ static int ref_set_non_owning(struct bpf_verifier_env *env, struct bpf_reg_state
 	struct bpf_verifier_state *state = env->cur_state;
 	struct btf_record *rec = reg_btf_record(reg);

-	if (!state->active_lock.ptr) {
+	if (!state->active_lock) {
 		verbose(env, "verifier internal error: ref_set_non_owning w/o active lock\n");
 		return -EFAULT;
 	}
@@ -11720,6 +11790,7 @@ static int ref_convert_owning_non_owning(struct bpf_verifier_env *env, u32 ref_o
  */
 static int check_reg_allocation_locked(struct bpf_verifier_env *env, struct bpf_reg_state *reg)
 {
+	struct bpf_reference_state *s;
 	void *ptr;
 	u32 id;

@@ -11736,10 +11807,10 @@ static int check_reg_allocation_locked(struct bpf_verifier_env *env, struct bpf_
 	}
 	id = reg->id;

-	if (!env->cur_state->active_lock.ptr)
+	if (!env->cur_state->active_lock)
 		return -EINVAL;
-	if (env->cur_state->active_lock.ptr != ptr ||
-	    env->cur_state->active_lock.id != id) {
+	s = find_lock_state(env, REF_TYPE_LOCK, id, ptr);
+	if (!s) {
 		verbose(env, "held lock and object are not in the same allocation\n");
 		return -EINVAL;
 	}
@@ -17635,8 +17706,22 @@ static bool refsafe(struct bpf_func_state *old, struct bpf_func_state *cur,
 		return false;

 	for (i = 0; i < old->acquired_refs; i++) {
-		if (!check_ids(old->refs[i].id, cur->refs[i].id, idmap))
+		if (!check_ids(old->refs[i].id, cur->refs[i].id, idmap) ||
+		    old->refs[i].type != cur->refs[i].type)
+			return false;
+		switch (old->refs[i].type) {
+		case REF_TYPE_PTR:
+			if (old->refs[i].callback_ref != cur->refs[i].callback_ref)
+				return false;
+			break;
+		case REF_TYPE_LOCK:
+			if (old->refs[i].ptr != cur->refs[i].ptr)
+				return false;
+			break;
+		default:
+			WARN_ONCE(1, "Unhandled enum type for reference state: %d\n", old->refs[i].type);
 			return false;
+		}
 	}

 	return true;
@@ -17714,17 +17799,7 @@ static bool states_equal(struct bpf_verifier_env *env,
 	if (old->speculative && !cur->speculative)
 		return false;

-	if (old->active_lock.ptr != cur->active_lock.ptr)
-		return false;
-
-	/* Old and cur active_lock's have to be either both present
-	 * or both absent.
-	 */
-	if (!!old->active_lock.id != !!cur->active_lock.id)
-		return false;
-
-	if (old->active_lock.id &&
-	    !check_ids(old->active_lock.id, cur->active_lock.id, &env->idmap_scratch))
+	if (old->active_lock != cur->active_lock)
 		return false;

 	if (old->active_rcu_lock != cur->active_rcu_lock)
@@ -18625,7 +18700,7 @@ static int do_check(struct bpf_verifier_env *env)
 					return -EINVAL;
 				}

-				if (env->cur_state->active_lock.ptr) {
+				if (env->cur_state->active_lock) {
 					if ((insn->src_reg == BPF_REG_0 && insn->imm != BPF_FUNC_spin_unlock) ||
 					    (insn->src_reg == BPF_PSEUDO_KFUNC_CALL &&
 					     (insn->off != 0 || !is_bpf_graph_api_kfunc(insn->imm)))) {
--
2.43.5

Re: [PATCH bpf-next v4] bpf: Refactor active lock management

[Alexei Starovoitov]

On Fri, Nov 8, 2024 at 11:43 PM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>  struct bpf_retval_range {
> @@ -434,7 +431,7 @@ struct bpf_verifier_state {
>         u32 insn_idx;
>         u32 curframe;
>
> -       struct bpf_active_lock active_lock;
> +       int active_lock;

What about this comment from v3:
> +       bool active_lock;

In the next patch it becomes 'int',
so let's make it 'int' right away and move it to bpf_func_state
next to:
        int acquired_refs;
        struct bpf_reference_state *refs;

?

wouldn't it be cleaner to keep the count of locks in bpf_func_state
next to refs ?

acquire_lock_state() would increment it and release will dec it.

check_resource_leak() will
instead of:
env->cur_state->active_lock
do:
cur_func(env)->active_lock

so behavior is the same, but counting of locks is clean.

Since in this patch it's kinda counting locks across all frames
which is a bit odd.

Re: [PATCH bpf-next v4] bpf: Refactor active lock management

[Kumar Kartikeya Dwivedi]

On Sat, 9 Nov 2024 at 22:30, Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Fri, Nov 8, 2024 at 11:43 PM Kumar Kartikeya Dwivedi
> <memxor@gmail.com> wrote:
> >  struct bpf_retval_range {
> > @@ -434,7 +431,7 @@ struct bpf_verifier_state {
> >         u32 insn_idx;
> >         u32 curframe;
> >
> > -       struct bpf_active_lock active_lock;
> > +       int active_lock;
>
> What about this comment from v3:
> > +       bool active_lock;
>
> In the next patch it becomes 'int',
> so let's make it 'int' right away and move it to bpf_func_state
> next to:
>         int acquired_refs;
>         struct bpf_reference_state *refs;
>
> ?

Ah, sorry, I somehow missed this part of the comment (twice). Mea culpa.

>
> wouldn't it be cleaner to keep the count of locks in bpf_func_state
> next to refs
>
> acquire_lock_state() would increment it and release will dec it.
>
> check_resource_leak() will
> instead of:
> env->cur_state->active_lock
> do:
> cur_func(env)->active_lock
>
> so behavior is the same, but counting of locks is clean.
>
> Since in this patch it's kinda counting locks across all frames
> which is a bit odd.

It would work, but we'd need to copy it over to a new frame's
bpf_func_state and copy it back on exit.
None of that would matter currently as only one lock can be held, but
it would become relevant later.

It's the same situation with reference states. It is inherited from
the parent frame for every new frame, and then possibly changed, and
then copied back to parent frame.

I have no preference either way, but if you think maintaining it as
part of func state is better I can make that change.

Re: [PATCH bpf-next v4] bpf: Refactor active lock management

[Alexei Starovoitov]

On Sat, Nov 9, 2024 at 1:38 PM Kumar Kartikeya Dwivedi <memxor@gmail.com> wrote:
>
> On Sat, 9 Nov 2024 at 22:30, Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > On Fri, Nov 8, 2024 at 11:43 PM Kumar Kartikeya Dwivedi
> > <memxor@gmail.com> wrote:
> > >  struct bpf_retval_range {
> > > @@ -434,7 +431,7 @@ struct bpf_verifier_state {
> > >         u32 insn_idx;
> > >         u32 curframe;
> > >
> > > -       struct bpf_active_lock active_lock;
> > > +       int active_lock;
> >
> > What about this comment from v3:
> > > +       bool active_lock;
> >
> > In the next patch it becomes 'int',
> > so let's make it 'int' right away and move it to bpf_func_state
> > next to:
> >         int acquired_refs;
> >         struct bpf_reference_state *refs;
> >
> > ?
>
> Ah, sorry, I somehow missed this part of the comment (twice). Mea culpa.
>
> >
> > wouldn't it be cleaner to keep the count of locks in bpf_func_state
> > next to refs
> >
> > acquire_lock_state() would increment it and release will dec it.
> >
> > check_resource_leak() will
> > instead of:
> > env->cur_state->active_lock
> > do:
> > cur_func(env)->active_lock
> >
> > so behavior is the same, but counting of locks is clean.
> >
> > Since in this patch it's kinda counting locks across all frames
> > which is a bit odd.
>
> It would work, but we'd need to copy it over to a new frame's
> bpf_func_state and copy it back on exit.
> None of that would matter currently as only one lock can be held, but
> it would become relevant later.
>
> It's the same situation with reference states. It is inherited from
> the parent frame for every new frame, and then possibly changed, and
> then copied back to parent frame.

Exactly, but since we're unifying held locks as references
would it make sense to treat them the same way everywhere?
active_lock is just a count of held locks in ref state.
For refs we do:
if (!exception_exit && state->in_callback_fn &&
state->refs[i].callback_ref != state->frameno)

so that
  task = task_acquire().
  bpf_loop(cb)
  task_release(task)
doesn't trip.

Wouldn't we want the same for locks eventually ?

Just if (env->cur_state->active_lock) will change obviously.
We may even need two counters for regular and resilient locks ?
And in that case two counters in bpf_verifier_state looks even more odd.
While two counters in bpf_func_state feels more logical.

Just trying to anticipate the future changes...

Re: [PATCH bpf-next v4] bpf: Refactor active lock management

[Kumar Kartikeya Dwivedi]

On Sat, 9 Nov 2024 at 23:02, Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Sat, Nov 9, 2024 at 1:38 PM Kumar Kartikeya Dwivedi <memxor@gmail.com> wrote:
> >
> > On Sat, 9 Nov 2024 at 22:30, Alexei Starovoitov
> > <alexei.starovoitov@gmail.com> wrote:
> > >
> > > On Fri, Nov 8, 2024 at 11:43 PM Kumar Kartikeya Dwivedi
> > > <memxor@gmail.com> wrote:
> > > >  struct bpf_retval_range {
> > > > @@ -434,7 +431,7 @@ struct bpf_verifier_state {
> > > >         u32 insn_idx;
> > > >         u32 curframe;
> > > >
> > > > -       struct bpf_active_lock active_lock;
> > > > +       int active_lock;
> > >
> > > What about this comment from v3:
> > > > +       bool active_lock;
> > >
> > > In the next patch it becomes 'int',
> > > so let's make it 'int' right away and move it to bpf_func_state
> > > next to:
> > >         int acquired_refs;
> > >         struct bpf_reference_state *refs;
> > >
> > > ?
> >
> > Ah, sorry, I somehow missed this part of the comment (twice). Mea culpa.
> >
> > >
> > > wouldn't it be cleaner to keep the count of locks in bpf_func_state
> > > next to refs
> > >
> > > acquire_lock_state() would increment it and release will dec it.
> > >
> > > check_resource_leak() will
> > > instead of:
> > > env->cur_state->active_lock
> > > do:
> > > cur_func(env)->active_lock
> > >
> > > so behavior is the same, but counting of locks is clean.
> > >
> > > Since in this patch it's kinda counting locks across all frames
> > > which is a bit odd.
> >
> > It would work, but we'd need to copy it over to a new frame's
> > bpf_func_state and copy it back on exit.
> > None of that would matter currently as only one lock can be held, but
> > it would become relevant later.
> >
> > It's the same situation with reference states. It is inherited from
> > the parent frame for every new frame, and then possibly changed, and
> > then copied back to parent frame.
>
> Exactly, but since we're unifying held locks as references
> would it make sense to treat them the same way everywhere?
> active_lock is just a count of held locks in ref state.
> For refs we do:
> if (!exception_exit && state->in_callback_fn &&
> state->refs[i].callback_ref != state->frameno)
>
> so that
>   task = task_acquire().
>   bpf_loop(cb)
>   task_release(task)
> doesn't trip.
>
> Wouldn't we want the same for locks eventually ?
>

This prompted me to dig into why (I) added that check. Turns out it
would no longer be necessary after Eduard fixed callback verification
some time ago.
It was a stop gap to prevent certain bad patterns since verifier
simulated a callback once. So preventing addition of references from
callback, and release of parent references prevented unsafe behavior
when callback actually ran N times. Now that's no longer necessary, so
I went ahead and dropped all of that cruft from the verifier, and the
selftests added back then still failed correctly.

Anyhow, all of it makes sense, so I went ahead and put active_locks as
part of bpf_func_state.



> Just if (env->cur_state->active_lock) will change obviously.
> We may even need two counters for regular and resilient locks ?
> And in that case two counters in bpf_verifier_state looks even more odd.
> While two counters in bpf_func_state feels more logical.
>
> Just trying to anticipate the future changes...