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22:55:28 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] sched/numa: add statistics of numa balance task migration Content-Language: en-GB To: "Chen, Yu C" , "Jain, Ayush" , Andrew Morton Cc: Ingo Molnar , Tejun Heo , Johannes Weiner , Jonathan Corbet , Mel Gorman , Michal Hocko , Michal Koutny , Muchun Song , Roman Gushchin , Shakeel Butt , "Chen, Tim C" , Aubrey Li , Libo Chen , cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, K Prateek Nayak , Madadi Vineeth Reddy , Neeraj.Upadhyay@amd.com, Peter Zijlstra , Madhavan Srinivasan References: <20250430103623.3349842-1-yu.c.chen@intel.com> <8b248ff3-43ae-4e40-9fa4-ba4a04f3c18b@amd.com> From: Venkat Rao Bagalkote In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: qoipdVZaZz7nT96xSUl1qc8aL2V8KBQW X-Authority-Analysis: v=2.4 cv=dMSmmPZb c=1 sm=1 tr=0 ts=6818f494 cx=c_pps 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https://web.git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/kernel/sched/core.c?id=3b2339eeb032627e9329daf70a4ba8cd62c9cc8d >> >> >> by looking at RIP pointer >> >> $ ./scripts/faddr2line vmlinux __migrate_swap_task+0x2e/0x180 >> __migrate_swap_task+0x2e/0x180: >> count_memcg_events_mm at include/linux/memcontrol.h:987 >> (inlined by) count_memcg_events_mm at include/linux/memcontrol.h:978 >> (inlined by) __migrate_swap_task at kernel/sched/core.c:3356 >> >> memcg = mem_cgroup_from_task(rcu_dereference(mm->owner)); >> mm->owner -> NULL >> >> Attaching kernel logs below: >> >> [ 1070.635450] rcu-torture: rcu_torture_read_exit: End of episode >> [ 1074.047617] BUG: kernel NULL pointer dereference, address: >> 0000000000000498 > > Thanks Ayush, > > According to this address, >    4c 8b af 50 09 00 00    mov    0x950(%rdi),%r13  <--- r13 = p->mm; >    49 8b bd 98 04 00 00    mov    0x498(%r13),%rdi  <--- p->mm->owner > It seems that this task to be swapped has NULL mm_struct. > > Does the following help? > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 96db6947bc92..0cb8cc4d551d 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -3353,7 +3353,8 @@ void set_task_cpu(struct task_struct *p, > unsigned int new_cpu) >  static void __migrate_swap_task(struct task_struct *p, int cpu) >  { >         __schedstat_inc(p->stats.numa_task_swapped); > -       count_memcg_event_mm(p->mm, NUMA_TASK_SWAP); > +       if (p->mm) > +               count_memcg_event_mm(p->mm, NUMA_TASK_SWAP); > >         if (task_on_rq_queued(p)) { >                 struct rq *src_rq, *dst_rq; > Hello Chenyu, This issue is reported even on IBM Power servers. Proposed fix works fine. Hence, Tested-by: Venkat Rao Bagalkote Regards, Venkat. > > > Hi Andrew, > May I know if we can hold this patch and not merge it for now, > besides this regression, Libo has another comment related to > this patch and I'll address it in next version. Sorry for > inconvenience. > > thanks, > Chenyu >