From: Dan Williams <dan.j.williams@intel.com>
To: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: "Verma, Vishal L" <vishal.l.verma@intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"jmorris@namei.org" <jmorris@namei.org>,
"tiwai@suse.de" <tiwai@suse.de>,
"sashal@kernel.org" <sashal@kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
"david@redhat.com" <david@redhat.com>, "bp@suse.de" <bp@suse.de>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
"jglisse@redhat.com" <jglisse@redhat.com>,
"zwisler@kernel.org" <zwisler@kernel.org>,
"mhocko@suse.com" <mhocko@suse.com>,
"Jiang, Dave" <dave.jiang@intel.com>,
"bhelgaas@google.com" <bhelgaas@google.com>,
"Busch, Keith" <keith.busch@intel.com>,
"thomas.lendacky@amd.com" <thomas.lendacky@amd.com>,
"Huang, Ying" <ying.huang@intel.com>,
"Wu, Fengguang" <fengguang.wu@intel.com>,
"baiyaowei@cmss.chinamobile.com"
<baiyaowei@cmss.chinamobile.com>
Subject: Re: [v5 0/3] "Hotremove" persistent memory
Date: Wed, 15 May 2019 17:42:42 -0700 [thread overview]
Message-ID: <CAPcyv4jj557QNNwyQ7ez+=PnURsnXk9cGZ11Mmihmtem2bJ-3A@mail.gmail.com> (raw)
In-Reply-To: <CA+CK2bCKcJjXo7BGAVxvbQNYQFSDVLH5aB=S9yTmZWEfexOvtg@mail.gmail.com>
On Wed, May 15, 2019 at 11:12 AM Pavel Tatashin
<pasha.tatashin@soleen.com> wrote:
>
> > Hi Pavel,
> >
> > I am working on adding this sort of a workflow into a new daxctl command
> > (daxctl-reconfigure-device)- this will allow changing the 'mode' of a
> > dax device to kmem, online the resulting memory, and with your patches,
> > also attempt to offline the memory, and change back to device-dax.
> >
> > In running with these patches, and testing the offlining part, I ran
> > into the following lockdep below.
> >
> > This is with just these three patches on top of -rc7.
> >
> >
> > [ +0.004886] ======================================================
> > [ +0.001576] WARNING: possible circular locking dependency detected
> > [ +0.001506] 5.1.0-rc7+ #13 Tainted: G O
> > [ +0.000929] ------------------------------------------------------
> > [ +0.000708] daxctl/22950 is trying to acquire lock:
> > [ +0.000548] 00000000f4d397f7 (kn->count#424){++++}, at: kernfs_remove_by_name_ns+0x40/0x80
> > [ +0.000922]
> > but task is already holding lock:
> > [ +0.000657] 000000002aa52a9f (mem_sysfs_mutex){+.+.}, at: unregister_memory_section+0x22/0xa0
>
> I have studied this issue, and now have a clear understanding why it
> happens, I am not yet sure how to fix it, so suggestions are welcomed
> :)
I would think that ACPI hotplug would have a similar problem, but it does this:
acpi_unbind_memory_blocks(info);
__remove_memory(nid, info->start_addr, info->length);
I wonder if that ordering prevents going too deep into the
device_unregister() call stack that you highlighted below.
>
> Here is the problem:
>
> When we offline pages we have the following call stack:
>
> # echo offline > /sys/devices/system/memory/memory8/state
> ksys_write
> vfs_write
> __vfs_write
> kernfs_fop_write
> kernfs_get_active
> lock_acquire kn->count#122 (lock for
> "memory8/state" kn)
> sysfs_kf_write
> dev_attr_store
> state_store
> device_offline
> memory_subsys_offline
> memory_block_action
> offline_pages
> __offline_pages
> percpu_down_write
> down_write
> lock_acquire mem_hotplug_lock.rw_sem
>
> When we unbind dax0.0 we have the following stack:
> # echo dax0.0 > /sys/bus/dax/drivers/kmem/unbind
> drv_attr_store
> unbind_store
> device_driver_detach
> device_release_driver_internal
> dev_dax_kmem_remove
> remove_memory device_hotplug_lock
> try_remove_memory mem_hotplug_lock.rw_sem
> arch_remove_memory
> __remove_pages
> __remove_section
> unregister_memory_section
> remove_memory_section mem_sysfs_mutex
> unregister_memory
> device_unregister
> device_del
> device_remove_attrs
> sysfs_remove_groups
> sysfs_remove_group
> remove_files
> kernfs_remove_by_name
> kernfs_remove_by_name_ns
> __kernfs_remove kn->count#122
>
> So, lockdep found the ordering issue with the above two stacks:
>
> 1. kn->count#122 -> mem_hotplug_lock.rw_sem
> 2. mem_hotplug_lock.rw_sem -> kn->count#122
next prev parent reply other threads:[~2019-05-16 0:42 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-02 18:43 [v5 0/3] "Hotremove" persistent memory Pavel Tatashin
2019-05-02 18:43 ` [v5 1/3] device-dax: fix memory and resource leak if hotplug fails Pavel Tatashin
2019-05-02 18:43 ` [v5 2/3] mm/hotplug: make remove_memory() interface useable Pavel Tatashin
2019-05-03 10:06 ` David Hildenbrand
2019-05-06 17:57 ` Dave Hansen
2019-05-06 18:01 ` Dan Williams
2019-05-06 18:04 ` Dave Hansen
2019-05-06 18:18 ` Pavel Tatashin
2019-05-17 18:10 ` Pavel Tatashin
2019-05-06 18:13 ` Pavel Tatashin
2019-05-02 18:43 ` [v5 3/3] device-dax: "Hotremove" persistent memory that is used like normal RAM Pavel Tatashin
2019-05-02 20:50 ` [v5 0/3] "Hotremove" persistent memory Verma, Vishal L
2019-05-02 21:44 ` Pavel Tatashin
2019-05-02 22:29 ` Verma, Vishal L
2019-05-02 22:36 ` Pavel Tatashin
2019-05-03 21:48 ` Verma, Vishal L
2019-05-15 18:11 ` Pavel Tatashin
2019-05-16 0:42 ` Dan Williams [this message]
2019-05-16 7:10 ` David Hildenbrand
2019-05-17 14:09 ` Pavel Tatashin
2019-05-20 7:57 ` David Hildenbrand
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