linux-kernel - Re: [RFC PATCH net-next] page_pool: Add page_pool_release

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Message-ID: <4f9b3183-1aa1-4506-b4dc-3297a8f19928@linux.dev>
Date: Wed, 26 Nov 2025 10:16:41 +0800
From: Leon Hwang <leon.hwang@...ux.dev>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: netdev@...r.kernel.org, hawk@...nel.org, ilias.apalodimas@...aro.org,
 mhiramat@...nel.org, mathieu.desnoyers@...icios.com, davem@...emloft.net,
 edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, horms@...nel.org,
 kerneljasonxing@...il.com, lance.yang@...ux.dev, jiayuan.chen@...ux.dev,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 Leon Huang Fu <leon.huangfu@...pee.com>
Subject: Re: [RFC PATCH net-next] page_pool: Add page_pool_release_stalled
 tracepoint



On 26/11/25 00:23, Steven Rostedt wrote:
> On Tue, 25 Nov 2025 16:22:07 +0800
> Leon Hwang <leon.hwang@...ux.dev> wrote:
> 
>> +TRACE_EVENT(page_pool_release_stalled,
>> +
>> +	TP_PROTO(const struct page_pool *pool, int inflight, int sec),
>> +
>> +	TP_ARGS(pool, inflight, sec),
>> +
>> +	TP_STRUCT__entry(
>> +		__field(const struct page_pool *, pool)
>> +		__field(int,			  inflight)
>> +		__field(int,			  sec)
>> +	),
>> +
>> +	TP_fast_assign(
>> +		__entry->pool		= pool;
>> +		__entry->inflight	= inflight;
>> +		__entry->sec		= sec;
>> +	),
>> +
>> +	TP_printk("page_pool=%p id=%d inflight=%d sec=%d",
>> +		  __entry->pool, __entry->pool->user.id, __entry->inflight, __entry->sec)
> 
> You can't do: __entry->pool->user.id
> 
> The TP_fast_assign() is executed when the tracepoint is triggered. The
> TP_printk() is executed when the trace is read. That can happen seconds,
> minutes, hours, days, even months after the pool was assigned.
> 
> That __entry->pool can very well be freed a long time ago.
> 
> If you need the id, you need to record it in the TP_fast_assign():
> 
> 	__entry->id		= pool->user.id
> 
> and print that.
> 
> -- Steve
> 

Hi Steve,

Thanks for the review.

Yes, the id is needed here (similar to what we emit in pr_warn()), so
I'll follow your suggestion and record it explicitly in TP_fast_assign():

	__entry->id		= pool->user.id;

And then update the print format to:

	TP_printk("page_pool=%p id=%d inflight=%d sec=%d",
		  __entry->pool, __entry->id,
		  __entry->inflight, __entry->sec)

Thanks,
Leon