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[209.132.183.28]) by mx.google.com with ESMTPS id t16si1044443qkt.220.2019.05.03.03.06.28 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 03 May 2019 03:06:28 -0700 (PDT) Received-SPF: pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D8B04C058CB4; Fri, 3 May 2019 10:06:26 +0000 (UTC) Received: from [10.36.117.87] (ovpn-117-87.ams2.redhat.com [10.36.117.87]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4D9AC60BF7; Fri, 3 May 2019 10:06:20 +0000 (UTC) Subject: Re: [v5 2/3] mm/hotplug: make remove_memory() interface useable To: Pavel Tatashin , jmorris@namei.org, sashal@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-nvdimm@lists.01.org, akpm@linux-foundation.org, mhocko@suse.com, dave.hansen@linux.intel.com, dan.j.williams@intel.com, keith.busch@intel.com, vishal.l.verma@intel.com, dave.jiang@intel.com, zwisler@kernel.org, thomas.lendacky@amd.com, ying.huang@intel.com, fengguang.wu@intel.com, bp@suse.de, bhelgaas@google.com, baiyaowei@cmss.chinamobile.com, tiwai@suse.de, jglisse@redhat.com References: <20190502184337.20538-1-pasha.tatashin@soleen.com> <20190502184337.20538-3-pasha.tatashin@soleen.com> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190502184337.20538-3-pasha.tatashin@soleen.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Fri, 03 May 2019 10:06:27 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 02.05.19 20:43, Pavel Tatashin wrote: > As of right now remove_memory() interface is inherently broken. It tries > to remove memory but panics if some memory is not offline. The problem > is that it is impossible to ensure that all memory blocks are offline as > this function also takes lock_device_hotplug that is required to > change memory state via sysfs. > The existing interface can actually work today by registering a hotplug notifier and rejecting any onlining attempts. But I agree that this way, the interface becomes more usable. > So, between calling this function and offlining all memory blocks there > is always a window when lock_device_hotplug is released, and therefore, > there is always a chance for a panic during this window. > > Make this interface to return an error if memory removal fails. This way > it is safe to call this function without panicking machine, and also > makes it symmetric to add_memory() which already returns an error. > > Signed-off-by: Pavel Tatashin > --- > include/linux/memory_hotplug.h | 8 +++-- > mm/memory_hotplug.c | 61 ++++++++++++++++++++++------------ > 2 files changed, 46 insertions(+), 23 deletions(-) > > diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h > index 8ade08c50d26..5438a2d92560 100644 > --- a/include/linux/memory_hotplug.h > +++ b/include/linux/memory_hotplug.h > @@ -304,7 +304,7 @@ static inline void pgdat_resize_init(struct pglist_data *pgdat) {} > extern bool is_mem_section_removable(unsigned long pfn, unsigned long nr_pages); > extern void try_offline_node(int nid); > extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages); > -extern void remove_memory(int nid, u64 start, u64 size); > +extern int remove_memory(int nid, u64 start, u64 size); > extern void __remove_memory(int nid, u64 start, u64 size); > > #else > @@ -321,7 +321,11 @@ static inline int offline_pages(unsigned long start_pfn, unsigned long nr_pages) > return -EINVAL; > } > > -static inline void remove_memory(int nid, u64 start, u64 size) {} > +static inline bool remove_memory(int nid, u64 start, u64 size) > +{ > + return -EBUSY; > +} > + > static inline void __remove_memory(int nid, u64 start, u64 size) {} > #endif /* CONFIG_MEMORY_HOTREMOVE */ > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 8c454e82d4f6..a826aededa1a 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -1778,9 +1778,10 @@ static int check_memblock_offlined_cb(struct memory_block *mem, void *arg) > endpa = PFN_PHYS(section_nr_to_pfn(mem->end_section_nr + 1))-1; > pr_warn("removing memory fails, because memory [%pa-%pa] is onlined\n", > &beginpa, &endpa); > - } > > - return ret; > + return -EBUSY; > + } > + return 0; > } > > static int check_cpu_on_node(pg_data_t *pgdat) > @@ -1843,19 +1844,9 @@ void try_offline_node(int nid) > } > EXPORT_SYMBOL(try_offline_node); > > -/** > - * remove_memory > - * @nid: the node ID > - * @start: physical address of the region to remove > - * @size: size of the region to remove > - * > - * NOTE: The caller must call lock_device_hotplug() to serialize hotplug > - * and online/offline operations before this call, as required by > - * try_offline_node(). > - */ > -void __ref __remove_memory(int nid, u64 start, u64 size) > +static int __ref try_remove_memory(int nid, u64 start, u64 size) > { > - int ret; > + int rc = 0; > > BUG_ON(check_hotplug_memory_range(start, size)); > > @@ -1863,13 +1854,13 @@ void __ref __remove_memory(int nid, u64 start, u64 size) > > /* > * All memory blocks must be offlined before removing memory. Check > - * whether all memory blocks in question are offline and trigger a BUG() > + * whether all memory blocks in question are offline and return error > * if this is not the case. > */ > - ret = walk_memory_range(PFN_DOWN(start), PFN_UP(start + size - 1), NULL, > - check_memblock_offlined_cb); > - if (ret) > - BUG(); > + rc = walk_memory_range(PFN_DOWN(start), PFN_UP(start + size - 1), NULL, > + check_memblock_offlined_cb); > + if (rc) > + goto done; > > /* remove memmap entry */ > firmware_map_remove(start, start + size, "System RAM"); > @@ -1879,14 +1870,42 @@ void __ref __remove_memory(int nid, u64 start, u64 size) > > try_offline_node(nid); > > +done: > mem_hotplug_done(); > + return rc; > } > > -void remove_memory(int nid, u64 start, u64 size) > +/** > + * remove_memory > + * @nid: the node ID > + * @start: physical address of the region to remove > + * @size: size of the region to remove > + * > + * NOTE: The caller must call lock_device_hotplug() to serialize hotplug > + * and online/offline operations before this call, as required by > + * try_offline_node(). > + */ > +void __remove_memory(int nid, u64 start, u64 size) > { > + > + /* > + * trigger BUG() is some memory is not offlined prior to calling this > + * function > + */ > + if (try_remove_memory(nid, start, size)) > + BUG(); > +} > + > +/* Remove memory if every memory block is offline, otherwise return false */ Comment is wrong "return false" > +int remove_memory(int nid, u64 start, u64 size) > +{ > + int rc; > + > lock_device_hotplug(); > - __remove_memory(nid, start, size); > + rc = try_remove_memory(nid, start, size); > unlock_device_hotplug(); > + > + return rc; > } > EXPORT_SYMBOL_GPL(remove_memory); > #endif /* CONFIG_MEMORY_HOTREMOVE */ > Looks sane to me Reviewed-by: David Hildenbrand -- Thanks, David / dhildenb