Merge branch 'introduce-bpf_wq'

Benjamin Tissoires says:

====================
Introduce bpf_wq

This is a followup of sleepable bpf_timer[0].

When discussing sleepable bpf_timer, it was thought that we should give
a try to bpf_wq, as the 2 APIs are similar but distinct enough to
justify a new one.

So here it is.

I tried to keep as much as possible common code in kernel/bpf/helpers.c
but I couldn't get away with code duplication in kernel/bpf/verifier.c.

This series introduces a basic bpf_wq support:
- creation is supported
- assignment is supported
- running a simple bpf_wq is also supported.

We will probably need to extend the API further with:
- a full delayed_work API (can be piggy backed on top with a correct
  flag)
- bpf_wq_cancel() <- apparently not, this is shooting ourself in the
  foot
- bpf_wq_cancel_sync() (for sleepable programs)
- documentation
---

For reference, the use cases I have in mind:

---

Basically, I need to be able to defer a HID-BPF program for the
following reasons (from the aforementioned patch):
1. defer an event:
   Sometimes we receive an out of proximity event, but the device can not
   be trusted enough, and we need to ensure that we won't receive another
   one in the following n milliseconds. So we need to wait those n
   milliseconds, and eventually re-inject that event in the stack.

2. inject new events in reaction to one given event:
   We might want to transform one given event into several. This is the
   case for macro keys where a single key press is supposed to send
   a sequence of key presses. But this could also be used to patch a
   faulty behavior, if a device forgets to send a release event.

3. communicate with the device in reaction to one event:
   We might want to communicate back to the device after a given event.
   For example a device might send us an event saying that it came back
   from sleeping state and needs to be re-initialized.

Currently we can achieve that by keeping a userspace program around,
raise a bpf event, and let that userspace program inject the events and
commands.
However, we are just keeping that program alive as a daemon for just
scheduling commands. There is no logic in it, so it doesn't really justify
an actual userspace wakeup. So a kernel workqueue seems simpler to handle.

bpf_timers are currently running in a soft IRQ context, this patch
series implements a sleppable context for them.

Cheers,
Benjamin

[0] https://lore.kernel.org/all/20240408-hid-bpf-sleepable-v6-0-0499ddd91b94@kernel.org/

Changes in v2:
- took previous review into account
- mainly dropped BPF_F_WQ_SLEEPABLE
- Link to v1: https://lore.kernel.org/r/20240416-bpf_wq-v1-0-c9e66092f842@kernel.org

====================

Link: https://lore.kernel.org/r/20240420-bpf_wq-v2-0-6c986a5a741f@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 12 insertions, 1 deletions

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 5034c1b4ded7..64bf0cf3ee95 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -185,7 +185,7 @@ struct bpf_map_ops {
 
 enum {
 	/* Support at most 10 fields in a BTF type */
-	BTF_FIELDS_MAX	   = 10,
+	BTF_FIELDS_MAX	   = 11,
 };
 
 enum btf_field_type {
@@ -202,6 +202,7 @@ enum btf_field_type {
 	BPF_GRAPH_NODE = BPF_RB_NODE | BPF_LIST_NODE,
 	BPF_GRAPH_ROOT = BPF_RB_ROOT | BPF_LIST_HEAD,
 	BPF_REFCOUNT   = (1 << 9),
+	BPF_WORKQUEUE  = (1 << 10),
 };
 
 typedef void (*btf_dtor_kfunc_t)(void *);
@@ -238,6 +239,7 @@ struct btf_record {
 	u32 field_mask;
 	int spin_lock_off;
 	int timer_off;
+	int wq_off;
 	int refcount_off;
 	struct btf_field fields[];
 };
@@ -312,6 +314,8 @@ static inline const char *btf_field_type_name(enum btf_field_type type)
 		return "bpf_spin_lock";
 	case BPF_TIMER:
 		return "bpf_timer";
+	case BPF_WORKQUEUE:
+		return "bpf_wq";
 	case BPF_KPTR_UNREF:
 	case BPF_KPTR_REF:
 		return "kptr";
@@ -340,6 +344,8 @@ static inline u32 btf_field_type_size(enum btf_field_type type)
 		return sizeof(struct bpf_spin_lock);
 	case BPF_TIMER:
 		return sizeof(struct bpf_timer);
+	case BPF_WORKQUEUE:
+		return sizeof(struct bpf_wq);
 	case BPF_KPTR_UNREF:
 	case BPF_KPTR_REF:
 	case BPF_KPTR_PERCPU:
@@ -367,6 +373,8 @@ static inline u32 btf_field_type_align(enum btf_field_type type)
 		return __alignof__(struct bpf_spin_lock);
 	case BPF_TIMER:
 		return __alignof__(struct bpf_timer);
+	case BPF_WORKQUEUE:
+		return __alignof__(struct bpf_wq);
 	case BPF_KPTR_UNREF:
 	case BPF_KPTR_REF:
 	case BPF_KPTR_PERCPU:
@@ -406,6 +414,7 @@ static inline void bpf_obj_init_field(const struct btf_field *field, void *addr)
 		/* RB_ROOT_CACHED 0-inits, no need to do anything after memset */
 	case BPF_SPIN_LOCK:
 	case BPF_TIMER:
+	case BPF_WORKQUEUE:
 	case BPF_KPTR_UNREF:
 	case BPF_KPTR_REF:
 	case BPF_KPTR_PERCPU:
@@ -525,6 +534,7 @@ static inline void zero_map_value(struct bpf_map *map, void *dst)
 void copy_map_value_locked(struct bpf_map *map, void *dst, void *src,
 			   bool lock_src);
 void bpf_timer_cancel_and_free(void *timer);
+void bpf_wq_cancel_and_free(void *timer);
 void bpf_list_head_free(const struct btf_field *field, void *list_head,
 			struct bpf_spin_lock *spin_lock);
 void bpf_rb_root_free(const struct btf_field *field, void *rb_root,
@@ -2195,6 +2205,7 @@ void bpf_map_free_record(struct bpf_map *map);
 struct btf_record *btf_record_dup(const struct btf_record *rec);
 bool btf_record_equal(const struct btf_record *rec_a, const struct btf_record *rec_b);
 void bpf_obj_free_timer(const struct btf_record *rec, void *obj);
+void bpf_obj_free_workqueue(const struct btf_record *rec, void *obj);
 void bpf_obj_free_fields(const struct btf_record *rec, void *obj);
 void __bpf_obj_drop_impl(void *p, const struct btf_record *rec, bool percpu);