Re: [PATCH] perf/core: fix mlock accounting in perf_mmap()

[Alexander Shishkin]

Song Liu <songliubraving@xxxxxx> writes:

>> On Jan 20, 2020, at 12:24 AM, Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx> wrote:
>> 
>> Song Liu <songliubraving@xxxxxx> writes:
>> 
>>> sysctl_perf_event_mlock and user->locked_vm can change value
>>> independently, so we can't guarantee:
>>> 
>>>    user->locked_vm <= user_lock_limit
>> 
>> This means: if the sysctl got sufficiently decreased, so that the
>> existing locked_vm exceeds it, we need to deal with the overflow, right?
>
> Reducing sysctl is one way to generate the overflow. Another way is to 
> call setrlimit() from user space to allow bigger user->locked_vm. 

You mean RLIMIT_MEMLOCK? That's a limit on mm->pinned_vm. Doesn't affect
user->locked_vm.

Regards,
--
Alex