From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8C5AFC433FE for ; Tue, 22 Nov 2022 15:24:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233922AbiKVPY5 (ORCPT ); Tue, 22 Nov 2022 10:24:57 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37234 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232628AbiKVPYu (ORCPT ); Tue, 22 Nov 2022 10:24:50 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3690432BB3 for ; Tue, 22 Nov 2022 07:23:52 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1669130631; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=SVY+XbYfUJix+mZbzWPjW0+C+/PxblVGhpQitKZ11Jw=; b=BzjsRVCjL5EfpCOMW+62ih9oHDYAHEscU93OmnqGsx/VsNNG3sIUT6SogcGvQo8fHqEWLd sM3o0JG8Djy6pbCFjKWlaQT+/GPO+XRicDpOPhZUx+fppVsq9lx8FY+uyNa5t1FM9geNU6 M1mAyTx2h84MZEAJ1ZA/xbgS+wiwDWo= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-589-O4q40dnSM3a75PhiWT7KCg-1; Tue, 22 Nov 2022 10:23:47 -0500 X-MC-Unique: O4q40dnSM3a75PhiWT7KCg-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 8BDA03C02584; Tue, 22 Nov 2022 15:23:46 +0000 (UTC) Received: from [10.22.17.223] (unknown [10.22.17.223]) by smtp.corp.redhat.com (Postfix) with ESMTP id CCE91C1908B; Tue, 22 Nov 2022 15:23:45 +0000 (UTC) Message-ID: <70b65b5b-385d-1c47-f003-1e42de290e86@redhat.com> Date: Tue, 22 Nov 2022 10:23:43 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.0 Subject: Re: [PATCH-tip] sched: Don't call kfree() in do_set_cpus_allowed() Content-Language: en-US To: Peter Zijlstra Cc: Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Phil Auld , linux-kernel@vger.kernel.org, Paul McKenney References: <20221118193302.522399-1-longman@redhat.com> <601640d0-9dc2-a060-e165-c8efac54aa34@redhat.com> From: Waiman Long In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/22/22 07:37, Peter Zijlstra wrote: > On Mon, Nov 21, 2022 at 10:04:33AM -0500, Waiman Long wrote: >> On 11/21/22 05:38, Peter Zijlstra wrote: >>> On Fri, Nov 18, 2022 at 02:33:02PM -0500, Waiman Long wrote: >>>> Commit 851a723e45d1 ("sched: Always clear user_cpus_ptr in >>>> do_set_cpus_allowed()") may call kfree() if user_cpus_ptr was previously >>>> set. Unfortunately, some of the callers of do_set_cpus_allowed() >>> 'some' ? There's only 3 or so, which one triggers this? >> It happenned at __kthread_bind_mask() where do_set_cpus_allowed() is called >> with pi_lock held. >> >> [ 1084.820105]  >> [ 1084.820110]  dump_stack_lvl+0x57/0x81 >> [ 1084.820117]  check_noncircular+0x103/0x120 >> [ 10[ 1084.820160]  lock_acquire+0xba/0x230 >> [ 1084.820164]  ? kfree+0x10f/0x380 >> [ 1084.820172]  ? do_set_cpus_allowed+0x40/0x60 >> [ 1084.820181]  rt_spin_lock+0x27/0xe0 >> [ 1084.820184]  ? kfree+0x10f/0x380 >> [ 1084.820188]  kfree+0x10f/0x380 >> [ 1084.820195]  do_set_cpus_allowed+0x40/0x60 >> [ 1084.820203]  kthread_bind_mask+0x4a/0x70 >> [ 1084.820211]  create_worker+0xfb/0x1a0 >> [ 1084.820220]  worker_thread+0x2e3/0x3c0 >> [ 1084.820226]  ? process_one_work+0x450/0x450 >> [ 1084.820230]  kthread+0x111/0x130 >> [ 1084.820236]  ? kthread_complete_and_exit+0x20/0x20 >> [ 1084.820244]  ret_from_fork+0x22/0x30 >> [ 1084.820258]  >> [ 1084.820260] BUG: sleeping function called from invalid context at >> kernel/locking/spinlock_rt.c:46 >> >> It shows up with PREEMPT_RT kernel. > Oh, I see .. > >> Maybe. One thing that I am not clear about is why user_cpus_ptr is set in >> the first place. > Perhaps someone set an affinity on kthreadd ? > > But I'm thinking this exact problem is also possible (rather more likely > even) with select_fallback_rq() that too holds pi_lock (which account > for both other users of this function). > > Bah. > > And the allocation is just the one long in size (for small configs) > which is just enough space for a single linked list like you had. That is exactly the reason why I use lockless list. > > Urgh. > > The below is yuck too, and I'm not sure Paul wants us to use > kvfree_call_rcu() without its wrapper. > > --- > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 78b2d5cabcc5..0d0af0fc7fcf 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2606,7 +2606,12 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask) > }; > > __do_set_cpus_allowed(p, &ac); > - kfree(ac.user_mask); > + /* > + * Because this is called with p->pi_lock held, it is not possible > + * to use kfree() here (when PREEMPT_RT=y), therefore punt to using > + * kfree_rcu(). > + */ > + kvfree_call_rcu((struct rcu_head *)ac.user_mask, (rcu_callback_t)0); > } I guess you need to do a NULL check before calling kvfree_call_rcu() as I don't think kvfree_call_rcu() does that. Also it is unlikely that we need to call it. > > int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src, > @@ -8196,7 +8201,7 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask) > struct affinity_context ac; > struct cpumask *user_mask; > struct task_struct *p; > - int retval; > + int retval, size; > > rcu_read_lock(); > > @@ -8229,7 +8234,11 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask) > if (retval) > goto out_put_task; > > - user_mask = kmalloc(cpumask_size(), GFP_KERNEL); > + /* > + * See do_set_cpus_allowed() for the rcu_head usage. > + */ > + size = max_t(int, cpumask_size(), sizeof(struct rcu_head)); > + user_mask = kmalloc(size, GFP_KERNEL); > if (!user_mask) { > retval = -ENOMEM; > goto out_put_task; I guess that will work too. Just like you, I am a bit uneasy to call into kvfree_call_rcu() directly as it may change in the future. How about iff --git a/kernel/sched/core.c b/kernel/sched/core.c index 78b2d5cabcc5..5fac4aa6ac7f 100644 --- a/kernel/sched/core.c diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 78b2d5cabcc5..5fac4aa6ac7f 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2593,6 +2593,11 @@ __do_set_cpus_allowed(struct task_struct *p, struct affinity_context *ctx)                 set_next_task(rq, p);  } +union cpumask_rcuhead { +       void *cpumask; +       struct rcu_head rcu; +}; +  /*   * Used for kthread_bind() and select_fallback_rq(), in both cases the user   * affinity (if any) should be destroyed too. @@ -2606,7 +2611,12 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)         };         __do_set_cpus_allowed(p, &ac); -       kfree(ac.user_mask); +       /* +        * Because this is called with p->pi_lock held, it is not possible +        * to use kfree() here (when PREEMPT_RT=y), therefore punt to using +        * kfree_rcu(). +        */ +       kfree_rcu((union cpumask_rcuhead *)ac.user_mask, rcu);  }  int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src, @@ -8196,7 +8206,7 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)         struct affinity_context ac;         struct cpumask *user_mask;         struct task_struct *p; -       int retval; +       int retval, size;         rcu_read_lock(); @@ -8229,7 +8239,11 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)         if (retval)                 goto out_put_task; -       user_mask = kmalloc(cpumask_size(), GFP_KERNEL); +       /* +        * See do_set_cpus_allowed() for the rcu_head usage. +        */ +       size = max_t(int, cpumask_size(), sizeof(union cpumask_rcuhead)); +       user_mask = kmalloc(size, GFP_KERNEL);         if (!user_mask) {                 retval = -ENOMEM;                 goto out_put_task; Cheers, Longman