From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ot0-f199.google.com (mail-ot0-f199.google.com [74.125.82.199]) by kanga.kvack.org (Postfix) with ESMTP id F3C726B0003 for ; Tue, 22 May 2018 13:25:14 -0400 (EDT) Received: by mail-ot0-f199.google.com with SMTP id r104-v6so15057184ota.19 for ; Tue, 22 May 2018 10:25:14 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id f127-v6sor8485126oia.177.2018.05.22.10.25.13 for (Google Transport Security); Tue, 22 May 2018 10:25:13 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <152694211402.5484.2277538346144115181.stgit@dwillia2-desk3.amr.corp.intel.com> <152694212460.5484.13180030631810166467.stgit@dwillia2-desk3.amr.corp.intel.com> <20180521161026.709d5f2876e44f151da3d179@linux-foundation.org> <860a8c46-5171-78ac-0255-ee1d21b16ce8@deltatee.com> From: Dan Williams Date: Tue, 22 May 2018 10:25:13 -0700 Message-ID: Subject: Re: [PATCH 2/5] mm, devm_memremap_pages: handle errors allocating final devres action Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Logan Gunthorpe Cc: Andrew Morton , stable , Christoph Hellwig , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Linux MM , Linux Kernel Mailing List On Tue, May 22, 2018 at 10:03 AM, Logan Gunthorpe wrote: > > > On 22/05/18 10:56 AM, Dan Williams wrote: >> On Tue, May 22, 2018 at 9:42 AM, Logan Gunthorpe wrote: >>> Hey Dan, >>> >>> On 21/05/18 06:07 PM, Dan Williams wrote: >>>> Without this change we could fail to register the teardown of >>>> devm_memremap_pages(). The likelihood of hitting this failure is tiny >>>> as small memory allocations almost always succeed. However, the impact >>>> of the failure is large given any future reconfiguration, or >>>> disable/enable, of an nvdimm namespace will fail forever as subsequent >>>> calls to devm_memremap_pages() will fail to setup the pgmap_radix >>>> since there will be stale entries for the physical address range. >>> >>> Sorry, I don't follow this. The change only seems to prevent a warning >>> from occurring in this situation. Won't pgmap_radix_release() still be >>> called regardless of whether this patch is applied? >> >> devm_add_action() does not call the release function, >> devm_add_action_or_reset() does. > > Oh, yes. Thanks I see that now. > >> Ah, true, good catch! >> >> We should manually kill in the !registered case. I think this means we >> need to pass in the custom kill routine, because for the pmem driver >> it's blk_freeze_queue_start(). > > It may be cleaner to just have the caller call the specific kill > function if devm_memremap_pages fails... As far as I can see by then it's too late, or we need to expose release details to the caller which defeats the purpose of devm semantics. > Though, I don't fully > understand how the nvdimm pmem driver cleans up the percpu counter. The dev_pagemap setup for pmem is entirely too subtle and arguably a layering violation as it reuses the block layer q_usage_counter percpu_ref. We arrange for that counter to be shutdown before the blk_cleanup_queue() does the same.