From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 94A5C299A8A for ; Thu, 3 Jul 2025 07:26:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751527584; cv=none; b=Ap3eNIyOGtZWwvD0HQhC4E30SvvIjLTYZhtvdMEBfnJNaEPRDLlpQQlIef3aBmYdIJ1FmTaPHWMzS73qdvAbKZIKHy3WF1oH47ddltqFOicU3NPTdv6WnVl0ah1FkZUqJNrJsEpfOSjwWfr/vrfkuw7dIC8DjO5y5zhZnvlx9ZE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751527584; c=relaxed/simple; bh=aZrQj1zi7sRaCxKaskG4fv/HM4jemIXDoUAASh3ewpY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=TJE5l/Yr/ix/SNpn614nnVoqOcg9MiHnnaAmikIfEN+XfDaAmFXwDLaim5i6QZAoDNNyAG9MKl8scKwhtLIXhJhvLPTdMJKmS5XwZP1Rw9gLhPOQJ+dIzqiTGGaT7rUo+izOvoiPufv71+v0SJSi+Wl0l95YC3AMyRMlq4qIUBM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=jA9jhBSE; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="jA9jhBSE" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=mO0u1JJhHr6e+vb3wOvor5wq8Jwna6+MzxSiR0enmxM=; b=jA9jhBSESNFY+sMB3BIw3uWr24 ukjZlN1BiunQJ0iWpg582oJgYYUCQ9yiLL0hL8YaeZh9MQAiqd7hbGiYczzpKN3yHY+GOu+pqRyvh 40gcbk1kSYjXMyzP+wcyhmsNKzJ0u+GDDLE1CpVLdSqDei58iog/BP0pzaCAi4fTJqQx15SG7fB3h SRXB7X4/s3M3XT7XrI5QyrmlWAGJeWg8JJ87/jTsPcLQAnYXRCTZTwUUtXTaPidMkBbJtsFddHP3O WerPJwMteWNE02AY3Dz0FWThARpTkbAELB7XQ+ggYWO6GERQayxy5hMVOaUvxyU+tbLs6NG/sUU/Q saYaewSA==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1uXEKg-00000007dbE-0Wev; Thu, 03 Jul 2025 07:26:10 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id C5D6F30017D; Thu, 03 Jul 2025 09:26:08 +0200 (CEST) Date: Thu, 3 Jul 2025 09:26:08 +0200 From: Peter Zijlstra To: Chen Yu Cc: Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Andrew Morton , Tim Chen , linux-kernel@vger.kernel.org, Jirka Hladky , Srikanth Aithal , Suneeth D , Libo Chen Subject: Re: [PATCH] sched/numa: Fix NULL pointer access to mm_struct durng task swap Message-ID: <20250703072608.GS1613200@noisy.programming.kicks-ass.net> References: <20250702163247.324439-1-yu.c.chen@intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250702163247.324439-1-yu.c.chen@intel.com> On Thu, Jul 03, 2025 at 12:32:47AM +0800, Chen Yu wrote: > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 8988d38d46a3..4e06bb955dad 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -3364,7 +3364,14 @@ static void __migrate_swap_task(struct task_struct *p, int cpu) > { > __schedstat_inc(p->stats.numa_task_swapped); > count_vm_numa_event(NUMA_TASK_SWAP); > - count_memcg_event_mm(p->mm, NUMA_TASK_SWAP); > + /* exiting task has NULL mm */ > + if (!(p->flags & PF_EXITING)) { > + WARN_ONCE(!p->mm, "swap task %d %s %x has no mm\n", > + p->pid, p->comm, p->flags); > + > + if (p->mm) > + count_memcg_event_mm(p->mm, NUMA_TASK_SWAP); > + } Aside from the things already mentioned by Andrew and Michal; why not simply do something like: diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 87b6688f124a..8396ebfab0d5 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -969,7 +969,7 @@ static inline void count_memcg_events_mm(struct mm_struct *mm, { struct mem_cgroup *memcg; - if (mem_cgroup_disabled()) + if (mem_cgroup_disabled() || !mm) return; rcu_read_lock();