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

[Hang Lu]

On 3/31/2021 3:44 PM, Greg KH wrote:
> 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 :(

Sorry for the late reply. Actually I add this as it needs to be enabled to protect against user-space that doesn't understand the new command, so I make it a global setting. But making this flag per-proc will gain a finer control granularity, so I'll follow your suggestion and submit a v2 patch, thanks!

Regards,
Hang Lu