I realized this while having a map containing both a struct bpf_timer and
a struct bpf_wq: the third argument provided to the bpf_wq callback is
not the struct bpf_wq pointer itself, but the pointer to the value in
the map.

Which means that the users need to double cast the provided "value" as
this is not a struct bpf_wq *.

This is a change of API, but there doesn't seem to be much users of bpf_wq
right now, so we should be able to go with this right now.

Fixes: 81f1d7a583fa ("bpf: wq: add bpf_wq_set_callback_impl")
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
---
 kernel/bpf/helpers.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 229396172026..5241ba671c5a 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2734,7 +2734,7 @@ __bpf_kfunc int bpf_wq_start(struct bpf_wq *wq, unsigned int flags)
 }
 
 __bpf_kfunc int bpf_wq_set_callback_impl(struct bpf_wq *wq,
-					 int (callback_fn)(void *map, int *key, struct bpf_wq *wq),
+					 int (callback_fn)(void *map, int *key, void *value),
 					 unsigned int flags,
 					 void *aux__ign)
 {

-- 
2.44.0

On Fri, 2024-07-05 at 15:44 +0200, Benjamin Tissoires wrote:
> I realized this while having a map containing both a struct bpf_timer and
> a struct bpf_wq: the third argument provided to the bpf_wq callback is
> not the struct bpf_wq pointer itself, but the pointer to the value in
> the map.
> 
> Which means that the users need to double cast the provided "value" as
> this is not a struct bpf_wq *.
> 
> This is a change of API, but there doesn't seem to be much users of bpf_wq
> right now, so we should be able to go with this right now.
> 
> Fixes: 81f1d7a583fa ("bpf: wq: add bpf_wq_set_callback_impl")
> Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
> ---

Reviewed-by: Eduard Zingerman <eddyz87@gmail.com>