Hi,
I am trying to add some debug information to rcu_head for some patches, and need
your help! At least this used to work some time ago (> 1 year).
I get various SLAB_MATCH() errors with a change like this:
diff --git a/include/linux/types.h b/include/linux/types.h
index ea8cf60a8a79..daf7682a7a3b 100644
--- a/include/linux/types.h
+++ b/include/linux/types.h
@@ -220,6 +220,7 @@ struct ustat {
struct callback_head {
struct callback_head *next;
void (*func)(struct callback_head *head);
+ char buf[4];
} __attribute__((aligned(sizeof(void *))));
#define rcu_head callback_head
---
Errors:
mm/slab.h:67:9: note: in expansion of macro ‘static_assert’
67 | static_assert(offsetof(struct page, pg) == offsetof(struct slab,
sl))
| ^~~~~~~~~~~~~
mm/slab.h:73:1: note: in expansion of macro ‘SLAB_MATCH’
73 | SLAB_MATCH(_refcount, __page_refcount);
| ^~~~~~~~~~
----------
I tried various things like increasing the struct slab or struct page size using
dummy variables, but nothing gives.
I tried to print the offsets of the struct using the compiler, but that requires
compilation to actually succeed. The same exercise with a pre-processor also
does not help because nested structures could also including rcu_heads.
If I at least knew how the offsets were off, I could hack it for my needs (of
course upstreaming such a change is a different story, but I do want to upstream
some variant of rcu_head debug info).
Any thoughts on how we can accomplish this?
Thanks!
- Joel
