From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 97CAD3314BC; Wed, 5 Nov 2025 15:18:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762355888; cv=none; b=AIjKl4n+mBzgQxQviyu6ty4Wm1WTOMTYMbrEhPNb7PTRMln8BaN8Puhz0ReO2Uvw0Tzg67ylTGshm8JFzkkRtW0HXYN0xuA6C92F0hGBcKqPBsSVbtG2L8e77edcHBZsLKuPoRB9rQcH8BhfvyFiWsLqCROf9bfv1RJgNrMdRfM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762355888; c=relaxed/simple; bh=KrTmSd/KLHnmJp6uY5VjqlnOzYc3oRuRzLcvqn1keFo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=hVQBnXI3+h2Ylt+7KrwPuN7LWEL125Ix4zWjX/ZOzTxa5NoGYzkEuNemfvMeK8BVbaax4J4tK/F9RW8j/dV03uAC9E456mzB12grK2nFkv4dDaGZELrF90F2JkVCL0BUZRPZI2djs6hIay6xxkKPmQsJ9o79a/mst+5/ZyYVFvs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VlA6UEYi; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="VlA6UEYi" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9B230C4CEF5; Wed, 5 Nov 2025 15:18:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1762355888; bh=KrTmSd/KLHnmJp6uY5VjqlnOzYc3oRuRzLcvqn1keFo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=VlA6UEYiwYN0luQ/4V7V5KntlUFeIZMU+NmpkL7d+M3N2iUQ1IOTeflqlF+lIm90q HiYedRgVi60NobljBr8hiMWKlKYaC0H2qpqcbgA62caHhlCZRV0lAw+K6rG/pGXCdM v2fUWpgA1cuUl7tJFOCWW5vd5SlcBeqwuZxogThAgO6JWjnfivWSGwf1FZmVbvLp51 DXvXopX+g369NCQ/HianrAkrAREQeoj/7Y3X5e7jN/22+bQDoRUOUhUSyljHri7cDD BYyWmWicrYUBAv0SObOJUefhS668cWVoSkzNKG1fBJO8d3jvGpTEthtLNQuTTZy+9f X1oSJavknulag== Date: Wed, 5 Nov 2025 16:18:05 +0100 From: Frederic Weisbecker To: Chen Ridong Cc: Waiman Long , LKML , Michal =?iso-8859-1?Q?Koutn=FD?= , Andrew Morton , Bjorn Helgaas , Catalin Marinas , Danilo Krummrich , "David S . Miller" , Eric Dumazet , Gabriele Monaco , Greg Kroah-Hartman , Ingo Molnar , Jakub Kicinski , Jens Axboe , Johannes Weiner , Lai Jiangshan , Marco Crivellari , Michal Hocko , Muchun Song , Paolo Abeni , Peter Zijlstra , Phil Auld , "Rafael J . Wysocki" , Roman Gushchin , Shakeel Butt , Simon Horman , Tejun Heo , Thomas Gleixner , Vlastimil Babka , Will Deacon , cgroups@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-block@vger.kernel.org, linux-mm@kvack.org, linux-pci@vger.kernel.org, netdev@vger.kernel.org Subject: Re: [PATCH 12/33] sched/isolation: Convert housekeeping cpumasks to rcu pointers Message-ID: References: <20251013203146.10162-1-frederic@kernel.org> <20251013203146.10162-13-frederic@kernel.org> <510b0185-51d6-44e6-8c39-dfc4c1721e03@redhat.com> <14cd347c-42c9-4134-9c1c-1a222b553c2f@huaweicloud.com> Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <14cd347c-42c9-4134-9c1c-1a222b553c2f@huaweicloud.com> Le Mon, Nov 03, 2025 at 10:22:47AM +0800, Chen Ridong a écrit : > > > On 2025/11/1 0:17, Frederic Weisbecker wrote: > > Le Tue, Oct 21, 2025 at 12:03:05AM -0400, Waiman Long a écrit : > >> On 10/20/25 9:46 PM, Chen Ridong wrote: > >>> > >>> On 2025/10/14 4:31, Frederic Weisbecker wrote: > >>>> HK_TYPE_DOMAIN's cpumask will soon be made modifyable by cpuset. > >>>> A synchronization mechanism is then needed to synchronize the updates > >>>> with the housekeeping cpumask readers. > >>>> > >>>> Turn the housekeeping cpumasks into RCU pointers. Once a housekeeping > >>>> cpumask will be modified, the update side will wait for an RCU grace > >>>> period and propagate the change to interested subsystem when deemed > >>>> necessary. > >>>> > >>>> Signed-off-by: Frederic Weisbecker > >>>> --- > >>>> kernel/sched/isolation.c | 58 +++++++++++++++++++++++++--------------- > >>>> kernel/sched/sched.h | 1 + > >>>> 2 files changed, 37 insertions(+), 22 deletions(-) > >>>> > >>>> diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c > >>>> index 8690fb705089..b46c20b5437f 100644 > >>>> --- a/kernel/sched/isolation.c > >>>> +++ b/kernel/sched/isolation.c > >>>> @@ -21,7 +21,7 @@ DEFINE_STATIC_KEY_FALSE(housekeeping_overridden); > >>>> EXPORT_SYMBOL_GPL(housekeeping_overridden); > >>>> struct housekeeping { > >>>> - cpumask_var_t cpumasks[HK_TYPE_MAX]; > >>>> + struct cpumask __rcu *cpumasks[HK_TYPE_MAX]; > >>>> unsigned long flags; > >>>> }; > >>>> @@ -33,17 +33,28 @@ bool housekeeping_enabled(enum hk_type type) > >>>> } > >>>> EXPORT_SYMBOL_GPL(housekeeping_enabled); > >>>> +const struct cpumask *housekeeping_cpumask(enum hk_type type) > >>>> +{ > >>>> + if (static_branch_unlikely(&housekeeping_overridden)) { > >>>> + if (housekeeping.flags & BIT(type)) { > >>>> + return rcu_dereference_check(housekeeping.cpumasks[type], 1); > >>>> + } > >>>> + } > >>>> + return cpu_possible_mask; > >>>> +} > >>>> +EXPORT_SYMBOL_GPL(housekeeping_cpumask); > >>>> + > >>>> int housekeeping_any_cpu(enum hk_type type) > >>>> { > >>>> int cpu; > >>>> if (static_branch_unlikely(&housekeeping_overridden)) { > >>>> if (housekeeping.flags & BIT(type)) { > >>>> - cpu = sched_numa_find_closest(housekeeping.cpumasks[type], smp_processor_id()); > >>>> + cpu = sched_numa_find_closest(housekeeping_cpumask(type), smp_processor_id()); > >>>> if (cpu < nr_cpu_ids) > >>>> return cpu; > >>>> - cpu = cpumask_any_and_distribute(housekeeping.cpumasks[type], cpu_online_mask); > >>>> + cpu = cpumask_any_and_distribute(housekeeping_cpumask(type), cpu_online_mask); > >>>> if (likely(cpu < nr_cpu_ids)) > >>>> return cpu; > >>>> /* > >>>> @@ -59,28 +70,18 @@ int housekeeping_any_cpu(enum hk_type type) > >>>> } > >>>> EXPORT_SYMBOL_GPL(housekeeping_any_cpu); > >>>> -const struct cpumask *housekeeping_cpumask(enum hk_type type) > >>>> -{ > >>>> - if (static_branch_unlikely(&housekeeping_overridden)) > >>>> - if (housekeeping.flags & BIT(type)) > >>>> - return housekeeping.cpumasks[type]; > >>>> - return cpu_possible_mask; > >>>> -} > >>>> -EXPORT_SYMBOL_GPL(housekeeping_cpumask); > >>>> - > >>>> void housekeeping_affine(struct task_struct *t, enum hk_type type) > >>>> { > >>>> if (static_branch_unlikely(&housekeeping_overridden)) > >>>> if (housekeeping.flags & BIT(type)) > >>>> - set_cpus_allowed_ptr(t, housekeeping.cpumasks[type]); > >>>> + set_cpus_allowed_ptr(t, housekeeping_cpumask(type)); > >>>> } > >>>> EXPORT_SYMBOL_GPL(housekeeping_affine); > >>>> bool housekeeping_test_cpu(int cpu, enum hk_type type) > >>>> { > >>>> - if (static_branch_unlikely(&housekeeping_overridden)) > >>>> - if (housekeeping.flags & BIT(type)) > >>>> - return cpumask_test_cpu(cpu, housekeeping.cpumasks[type]); > >>>> + if (housekeeping.flags & BIT(type)) > >>>> + return cpumask_test_cpu(cpu, housekeeping_cpumask(type)); > >>>> return true; > >>>> } > >>>> EXPORT_SYMBOL_GPL(housekeeping_test_cpu); > >>>> @@ -96,20 +97,33 @@ void __init housekeeping_init(void) > >>>> if (housekeeping.flags & HK_FLAG_KERNEL_NOISE) > >>>> sched_tick_offload_init(); > >>>> - > >>>> + /* > >>>> + * Realloc with a proper allocator so that any cpumask update > >>>> + * can indifferently free the old version with kfree(). > >>>> + */ > >>>> for_each_set_bit(type, &housekeeping.flags, HK_TYPE_MAX) { > >>>> + struct cpumask *omask, *nmask = kmalloc(cpumask_size(), GFP_KERNEL); > >>>> + > >>>> + if (WARN_ON_ONCE(!nmask)) > >>>> + return; > >>>> + > >>>> + omask = rcu_dereference(housekeeping.cpumasks[type]); > >>>> + > >>>> /* We need at least one CPU to handle housekeeping work */ > >>>> - WARN_ON_ONCE(cpumask_empty(housekeeping.cpumasks[type])); > >>>> + WARN_ON_ONCE(cpumask_empty(omask)); > >>>> + cpumask_copy(nmask, omask); > >>>> + RCU_INIT_POINTER(housekeeping.cpumasks[type], nmask); > >>>> + memblock_free(omask, cpumask_size()); > >>>> } > >>>> } > >>>> static void __init housekeeping_setup_type(enum hk_type type, > >>>> cpumask_var_t housekeeping_staging) > >>>> { > >>>> + struct cpumask *mask = memblock_alloc_or_panic(cpumask_size(), SMP_CACHE_BYTES); > >>>> - alloc_bootmem_cpumask_var(&housekeeping.cpumasks[type]); > >>>> - cpumask_copy(housekeeping.cpumasks[type], > >>>> - housekeeping_staging); > >>>> + cpumask_copy(mask, housekeeping_staging); > >>>> + RCU_INIT_POINTER(housekeeping.cpumasks[type], mask); > >>>> } > >>>> static int __init housekeeping_setup(char *str, unsigned long flags) > >>>> @@ -162,7 +176,7 @@ static int __init housekeeping_setup(char *str, unsigned long flags) > >>>> for_each_set_bit(type, &iter_flags, HK_TYPE_MAX) { > >>>> if (!cpumask_equal(housekeeping_staging, > >>>> - housekeeping.cpumasks[type])) { > >>>> + housekeeping_cpumask(type))) { > >>>> pr_warn("Housekeeping: nohz_full= must match isolcpus=\n"); > >>>> goto free_housekeeping_staging; > >>>> } > >>>> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > >>>> index 1f5d07067f60..0c0ef8999fd6 100644 > >>>> --- a/kernel/sched/sched.h > >>>> +++ b/kernel/sched/sched.h > >>>> @@ -42,6 +42,7 @@ > >>>> #include > >>>> #include > >>>> #include > >>>> +#include > >>>> #include > >>>> #include > >>>> #include > >>> A warning was detected: > >>> > >>> ============================= > >>> WARNING: suspicious RCU usage > >>> 6.17.0-next-20251009-00033-g4444da88969b #808 Not tainted > >>> ----------------------------- > >>> kernel/sched/isolation.c:60 suspicious rcu_dereference_check() usage! > >>> > >>> other info that might help us debug this: > >>> > >>> > >>> rcu_scheduler_active = 2, debug_locks = 1 > >>> 1 lock held by swapper/0/1: > >>> #0: ffff888100600ce0 (&type->i_mutex_dir_key#3){++++}-{4:4}, at: walk_compone > >>> > >>> stack backtrace: > >>> CPU: 3 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.17.0-next-20251009-00033-g4 > >>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239 > >>> Call Trace: > >>> > >>> dump_stack_lvl+0x68/0xa0 > >>> lockdep_rcu_suspicious+0x148/0x1b0 > >>> housekeeping_cpumask+0xaa/0xb0 > >>> housekeeping_test_cpu+0x25/0x40 > >>> find_get_block_common+0x41/0x3e0 > >>> bdev_getblk+0x28/0xa0 > >>> ext4_getblk+0xba/0x2d0 > >>> ext4_bread_batch+0x56/0x170 > >>> __ext4_find_entry+0x17c/0x410 > >>> ? lock_release+0xc6/0x290 > >>> ext4_lookup+0x7a/0x1d0 > >>> __lookup_slow+0xf9/0x1b0 > >>> walk_component+0xe0/0x150 > >>> link_path_walk+0x201/0x3e0 > >>> path_openat+0xb1/0xb30 > >>> ? stack_depot_save_flags+0x41e/0xa00 > >>> do_filp_open+0xbc/0x170 > >>> ? _raw_spin_unlock_irqrestore+0x2c/0x50 > >>> ? __create_object+0x59/0x80 > >>> ? trace_kmem_cache_alloc+0x1d/0xa0 > >>> ? vprintk_emit+0x2b2/0x360 > >>> do_open_execat+0x56/0x100 > >>> alloc_bprm+0x1a/0x200 > >>> ? __pfx_kernel_init+0x10/0x10 > >>> kernel_execve+0x4b/0x160 > >>> kernel_init+0xe5/0x1c0 > >>> ret_from_fork+0x185/0x1d0 > >>> ? __pfx_kernel_init+0x10/0x10 > >>> ret_from_fork_asm+0x1a/0x30 > >>> > >>> random: crng init done > >>> > >> It is because bh_lru_install() of fs/buffer.c calls cpu_is_isolated() > >> without holding a rcu_read_lock. Will need to add a rcu_read_lock() there. > > > > But this is called within bh_lru_lock() which should have either disabled > > IRQs or preemption off. I would expect rcu_dereference_check() to automatically > > verify those implied RCU read-side critical sections. > > > > Let's see, lockdep_assert_in_rcu_reader() checks preemptible(), which is: > > > > #define preemptible() (preempt_count() == 0 && !irqs_disabled()) > > > > Ah but if !CONFIG_PREEMPT_COUNT: > > > > #define preemptible() 0 > > > > Chen did you have !CONFIG_PREEMPT_COUNT ? > > > > Probably lockdep_assert_in_rcu_reader() should be fixed accordingly and consider > > preemption always disabled whenever !CONFIG_PREEMPT_COUNT. Let me check that... > > > > Thanks. > > > > I compiled with CONFIG_PREEMPT_COUNT=y and CONFIG_SMP=y. Oh actually I think it's my fault. This should be fixed with this: diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c index 95d69c2102f6..b2cb75513336 100644 --- a/kernel/sched/isolation.c +++ b/kernel/sched/isolation.c @@ -56,8 +56,8 @@ static bool housekeeping_dereference_check(enum hk_type type) static inline struct cpumask *housekeeping_cpumask_dereference(enum hk_type type) { - return rcu_dereference_check(housekeeping.cpumasks[type], - housekeeping_dereference_check(type)); + return rcu_dereference_all_check(housekeeping.cpumasks[type], + housekeeping_dereference_check(type)); } const struct cpumask *housekeeping_cpumask(enum hk_type type)