From: Qian Cai <cai@lca.pw>
To: David Hildenbrand <david@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
stable <stable@vger.kernel.org>,
Vishal Verma <vishal.l.verma@intel.com>,
Pavel Tatashin <pasha.tatashin@soleen.com>,
Michal Hocko <mhocko@suse.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Linux MM <linux-mm@kvack.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Greg KH <gregkh@linuxfoundation.org>
Subject: Re: [PATCH v4] mm/memory_hotplug: Fix remove_memory() lockdep splat
Date: Sat, 11 Jan 2020 08:55:59 -0500 [thread overview]
Message-ID: <0BE8F7EF-01DC-47BD-899B-11FB8B40EB0A@lca.pw> (raw)
In-Reply-To: <a3d58f0b-145f-1e70-434f-e97e1f08ebcf@redhat.com>
> On Jan 11, 2020, at 6:03 AM, David Hildenbrand <david@redhat.com> wrote:
>
> So I just remember why I think this (and the previously reported done
> for ACPI DIMMs) are false positives. The actual locking order is
>
> onlining/offlining from user space:
>
> kn->count -> device_hotplug_lock -> cpu_hotplug_lock -> mem_hotplug_lock
>
> memory removal:
>
> device_hotplug_lock -> cpu_hotplug_lock -> mem_hotplug_lock -> kn->count
>
>
> This looks like a locking inversion - but it's not. Whenever we come via
> user space we do a mutex_trylock(), which resolves this issue by backing
> up. The device_hotplug_lock will prevent
>
> I have no clue why the device_hotplug_lock does not pop up in the
> lockdep report here. Sounds wrong to me.
>
> I think this is a false positive and not stable material.
The point is that there are other paths does kn->count —> cpu_hotplug_lock without needing device_hotplug_lock to race with memory removal.
kmem_cache_shrink_all+0x50/0x100 (cpu_hotplug_lock.rw_sem/mem_hotplug_lock.rw_sem)
shrink_store+0x34/0x60
slab_attr_store+0x6c/0x170
sysfs_kf_write+0x70/0xb0
kernfs_fop_write+0x11c/0x270 ((kn->count)
__vfs_write+0x3c/0x70
vfs_write+0xcc/0x200
ksys_write+0x7c/0x140
system_call+0x5c/0x6
next prev parent reply other threads:[~2020-01-11 13:56 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-10 21:22 [PATCH v4] mm/memory_hotplug: Fix remove_memory() lockdep splat Dan Williams
2020-01-10 22:33 ` David Hildenbrand
2020-01-10 23:29 ` Dan Williams
2020-01-10 23:29 ` Dan Williams
2020-01-11 11:03 ` David Hildenbrand
2020-01-11 13:55 ` Qian Cai [this message]
2020-01-11 14:25 ` David Hildenbrand
2020-01-11 14:52 ` David Hildenbrand
2020-01-11 17:41 ` Dan Williams
2020-01-11 17:41 ` Dan Williams
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