Re: [PATCH 6.6.y] kprobes: consistent rcu api usage for kretprobe holder

[Greg KH <greg@kroah.com>]

On Wed, Dec 06, 2023 at 10:57:11AM +0900, mhiramat@kernel.org wrote:
> From: JP Kobryn <inwardvessel@gmail.com>
> 
> It seems that the pointer-to-kretprobe "rp" within the kretprobe_holder is
> RCU-managed, based on the (non-rethook) implementation of get_kretprobe().
> The thought behind this patch is to make use of the RCU API where possible
> when accessing this pointer so that the needed barriers are always in place
> and to self-document the code.
> 
> The __rcu annotation to "rp" allows for sparse RCU checking. Plain writes
> done to the "rp" pointer are changed to make use of the RCU macro for
> assignment. For the single read, the implementation of get_kretprobe()
> is simplified by making use of an RCU macro which accomplishes the same,
> but note that the log warning text will be more generic.
> 
> I did find that there is a difference in assembly generated between the
> usage of the RCU macros vs without. For example, on arm64, when using
> rcu_assign_pointer(), the corresponding store instruction is a
> store-release (STLR) which has an implicit barrier. When normal assignment
> is done, a regular store (STR) is found. In the macro case, this seems to
> be a result of rcu_assign_pointer() using smp_store_release() when the
> value to write is not NULL.
> 
> Link: https://lore.kernel.org/all/20231122132058.3359-1-inwardvessel@gmail.com/
> 
> Fixes: d741bf41d7c7 ("kprobes: Remove kretprobe hash")
> Cc: stable@vger.kernel.org
> Signed-off-by: JP Kobryn <inwardvessel@gmail.com>
> Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> (cherry picked from commit d839a656d0f3caca9f96e9bf912fd394ac6a11bc)
> ---
>  include/linux/kprobes.h | 8 +++-----
>  kernel/kprobes.c        | 4 ++--
>  2 files changed, 5 insertions(+), 7 deletions(-)

Did you build this?  It breaks the build in 6.6.y in horrible ways:

./include/linux/kprobes.h:145:33: error: field ‘pool’ has incomplete type
  145 |         struct objpool_head     pool;
      |                                 ^~~~


I'll drop this, can you please provide a working version?

thanks,

greg k-h