linux-kernel - Re: [PATCH v4 2/2] sched/numa: Add tracepoint that tracks the skipping of numa balancing due to cpuset memory pinning

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Message-ID: <20250423210108.5b2452ad@gandalf.local.home>
Date: Wed, 23 Apr 2025 21:01:08 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Libo Chen <libo.chen@...cle.com>
Cc: akpm@...ux-foundation.org, peterz@...radead.org, mgorman@...e.de,
 mingo@...hat.com, juri.lelli@...hat.com, vincent.guittot@...aro.org,
 tj@...nel.org, llong@...hat.com, sraithal@....com, venkat88@...ux.ibm.com,
 kprateek.nayak@....com, raghavendra.kt@....com, yu.c.chen@...el.com,
 tim.c.chen@...el.com, vineethr@...ux.ibm.com, chris.hyser@...cle.com,
 daniel.m.jordan@...cle.com, lorenzo.stoakes@...cle.com, mkoutny@...e.com,
 linux-mm@...ck.org, cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] sched/numa: Add tracepoint that tracks the
 skipping of numa balancing due to cpuset memory pinning

On Wed, 23 Apr 2025 17:36:30 -0700
Libo Chen <libo.chen@...cle.com> wrote:

> >> +	TP_fast_assign(
> >> +		memcpy(__entry->comm, tsk->comm, TASK_COMM_LEN);
> >> +		__entry->pid		 = task_pid_nr(tsk);
> >> +		__entry->tgid		 = task_tgid_nr(tsk);
> >> +		__entry->ngid		 = task_numa_group_id(tsk);
> >> +		memcpy(__entry->mem_allowed, mem_allowed_ptr->bits,
> >> +		       sizeof(__entry->mem_allowed));  
> > 
> > Is mem_allowed->bits guaranteed to be the size of BITS_TO_LONGS(MAX_NUM_NODES)
> > in size? If not, then memcpy will read beyond that size.
> >   
> 
> Yes, evidence can be found in the definitions of nodemask_t and DECLARE_BITMAP:
> 
> // include/linux/nodemask_types.h 
> typedef struct { DECLARE_BITMAP(bits, MAX_NUMNODES); } nodemask_t;
> 
> // include/linux/types.h
> #define DECLARE_BITMAP(name,bits) \
> 	unsigned long name[BITS_TO_LONGS(bits)]
> 

Hmm, I wonder then if we should add in TP_fast_assign():

	BUILD_BUG_ON(sizeof(nodemask_t) != BITS_TO_LONGS(MAX_NUM_NODES) * sizeof(long));

-- Steve