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Date: Fri, 24 Jan 2020 10:04:52 -0800 From: Dan Williams <dan.j.williams@...el.com> To: Michal Hocko <mhocko@...nel.org> Cc: David Hildenbrand <david@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>, stable <stable@...r.kernel.org>, Vishal Verma <vishal.l.verma@...el.com>, Pavel Tatashin <pasha.tatashin@...een.com>, Dave Hansen <dave.hansen@...ux.intel.com>, Linux MM <linux-mm@...ck.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] mm/memory_hotplug: Fix remove_memory() lockdep splat On Fri, Jan 24, 2020 at 4:56 AM Michal Hocko <mhocko@...nel.org> wrote: > > On Fri 10-01-20 13:27:24, Dan Williams wrote: > > On Fri, Jan 10, 2020 at 9:42 AM David Hildenbrand <david@...hat.com> wrote: > [...] > > > For your reference (roughly 5 months ago, so not that old) > > > > > > https://lkml.kernel.org/r/20190724143017.12841-1-david@redhat.com > > > > Oh, now I see the problem. You need to add that lock so far away from > > the __add_memory() to avoid lock inversion problems with the > > acpi_scan_lock. The organization I was envisioning would not work > > without deeper refactoring. > > Sorry to come back to this late. Has this been resolved? The mem_hotplug_lock lockdep splat fix in this patch has not landed. David and I have not quite come to consensus on how to resolve online racing removal. IIUC David wants that invalidation to be pages_correctly_probed(), I would prefer it to be directly tied to the object, struct memory_block, that remove_memory_block_devices() has modified, mem->section_count = 0. ...or are you referring to the discussion about acpi_scan_lock()? I came around to agreeing with your position that documenting was better than adding superfluous locking especially because the acpi_scan_lock() is take so far away from where the device_hotplug lock is needed.
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