Re: [PATCH] binder: tell userspace to dump current backtrace when detecting oneway spamming

[Greg KH]

On Wed, Mar 31, 2021 at 03:34:16PM +0800, Hang Lu wrote:
> When async binder buffer got exhausted, some normal oneway transaction
> will also be discarded and finally caused system/app stop. By that time,
> the binder debug information we dump may not relevant to the root cause.
> And this issue is difficult to debug if without the backtrace of thread
> sending spam.
> 
> This change will send BR_ONEWAY_SPAM_SUSPECT to userspace when detecting
> oneway spamming, request to dump current backtrace. The detection will
> happened only once when exceeding the threshold (target process dips
> below 80% of its oneway space, and current process is responsible for
> either more than 50 transactions, or more than 50% of the oneway space).
> And the detection will restart when the async buffer has returned to a
> healthy state.
> 
> Signed-off-by: Hang Lu <hangl@xxxxxxxxxxxxxx>
> ---
>  drivers/android/binder.c            | 25 ++++++++++++++++++++++---
>  drivers/android/binder_alloc.c      | 15 ++++++++++++---
>  drivers/android/binder_alloc.h      |  8 +++++++-
>  drivers/android/binder_internal.h   |  1 +
>  include/uapi/linux/android/binder.h |  8 ++++++++
>  5 files changed, 50 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index c119736..28ceaf9 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -87,6 +87,7 @@ static DEFINE_SPINLOCK(binder_dead_nodes_lock);
>  static struct dentry *binder_debugfs_dir_entry_root;
>  static struct dentry *binder_debugfs_dir_entry_proc;
>  static atomic_t binder_last_id;
> +static bool oneway_spam_detection_enabled;

Why is this a "whole system" value and not a "per binder instance"
value?  You just allowed one binder instance to affect another one,
which does not seem like a good idea to me :(

thanks,

greg k-h