linux-kernel - Re: [PATCH linux-next] perf/ring_buffer: Add EPOLLRDNORM flag for poll

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <87b67a79-d97e-4f81-9bf2-aa34d613b5bf@linux.dev>
Date: Fri, 14 Mar 2025 01:03:13 +0800
From: Tao Chen <chen.dylane@...ux.dev>
To: Ingo Molnar <mingo@...nel.org>
Cc: peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
 namhyung@...nel.org, mark.rutland@....com,
 alexander.shishkin@...ux.intel.com, jolsa@...nel.org, irogers@...gle.com,
 adrian.hunter@...el.com, kan.liang@...ux.intel.com,
 linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH linux-next] perf/ring_buffer: Add EPOLLRDNORM flag for
 poll

在 2025/3/13 18:05, Ingo Molnar 写道:
> 
> * Tao Chen <chen.dylane@...ux.dev> wrote:
> 
>> The poll man page says POLLRDNORM is equivalent to POLLIN,
>> so add EPOLLRDNORM here.
>>
>> Signed-off-by: Tao Chen <chen.dylane@...ux.dev>
>> ---
>>   kernel/events/ring_buffer.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
>> index 59a52b1a1..5130b119d 100644
>> --- a/kernel/events/ring_buffer.c
>> +++ b/kernel/events/ring_buffer.c
>> @@ -19,7 +19,7 @@
>>   
>>   static void perf_output_wakeup(struct perf_output_handle *handle)
>>   {
>> -	atomic_set(&handle->rb->poll, EPOLLIN);
>> +	atomic_set(&handle->rb->poll, EPOLLIN | EPOLLRDNORM);
> 
> So what does EPOLLRDNORM mean to begin with? There doesn't seem to be
> separate/specific handling of it anywhere in the kernel that I can
> see...
> 

It seems that if user set pollfd with POLLRDNORM, perf_poll will not 
return until timeout even if perf_output_wakeup called, whereas POLLIN 
returns.

> Thanks,
> 
> 	Ingo


-- 
Best Regards
Tao Chen