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[62.201.165.239]) by smtp.gmail.com with ESMTPSA id t6-v6sm11123934wmf.8.2018.08.13.08.46.49 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 13 Aug 2018 08:46:50 -0700 (PDT) Received: from d104.suse.de (nat.nue.novell.com [195.135.221.2]) by techadventures.net (Postfix) with ESMTPA id 0165412485F; Mon, 13 Aug 2018 17:46:48 +0200 (CEST) From: osalvador@techadventures.net To: akpm@linux-foundation.org Cc: mhocko@suse.com, dan.j.williams@intel.com, jglisse@redhat.com, rafael@kernel.org, david@redhat.com, yasu.isimatu@gmail.com, logang@deltatee.com, dave.jiang@intel.com, Jonathan.Cameron@huawei.com, vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Oscar Salvador Subject: [PATCH v2 3/3] mm/memory_hotplug: Refactor unregister_mem_sect_under_nodes Date: Mon, 13 Aug 2018 17:46:39 +0200 Message-Id: <20180813154639.19454-4-osalvador@techadventures.net> X-Mailer: git-send-email 2.13.6 In-Reply-To: <20180813154639.19454-1-osalvador@techadventures.net> References: <20180813154639.19454-1-osalvador@techadventures.net> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Oscar Salvador unregister_mem_sect_under_nodes() tries to allocate a nodemask_t in order to check whithin the loop which nodes have already been unlinked, so we do not repeat the operation on them. NODEMASK_ALLOC calls kmalloc() if NODES_SHIFT > 8, otherwise it just declares a nodemask_t variable whithin the stack. Since kamlloc() can fail, we actually check whether NODEMASK_ALLOC failed or not, and we return -ENOMEM accordingly. remove_memory_section() does not check for the return value though. The problem with this is that if we return -ENOMEM, it means that unregister_mem_sect_under_nodes will not be able to remove the symlinks, but since we do not check the return value, we go ahead and we call unregister_memory(), which will remove all the mem_blks directories. This will leave us with dangled symlinks. The easiest way to overcome this is to fallback by calling sysfs_remove_link() unconditionally in case NODEMASK_ALLOC failed. This means that we will call sysfs_remove_link on nodes that have been already unlinked, but nothing wrong happens as sysfs_remove_link() backs off somewhere down the chain in case the link has already been removed. I think that this is better than a) dangled symlinks b) having to recovery from such error in remove_memory_section Since from now on we will not need to take care about return values, we can make the function void. While at it, we can also drop the node_online() check, as a node can only be offline if all the memory/cpus associated with it have been removed. As we have a safe fallback, one thing that could also be done is to add __GFP_NORETRY in the flags when calling NODEMASK_ALLOC, so we do not retry. Signed-off-by: Oscar Salvador --- drivers/base/node.c | 26 +++++++++++++++----------- include/linux/node.h | 5 ++--- 2 files changed, 17 insertions(+), 14 deletions(-) diff --git a/drivers/base/node.c b/drivers/base/node.c index dd3bdab230b2..0a3ca62687ea 100644 --- a/drivers/base/node.c +++ b/drivers/base/node.c @@ -449,35 +449,39 @@ int register_mem_sect_under_node(struct memory_block *mem_blk, void *arg) } /* unregister memory section under all nodes that it spans */ -int unregister_mem_sect_under_nodes(struct memory_block *mem_blk, +void unregister_mem_sect_under_nodes(struct memory_block *mem_blk, unsigned long phys_index) { NODEMASK_ALLOC(nodemask_t, unlinked_nodes, GFP_KERNEL); unsigned long pfn, sect_start_pfn, sect_end_pfn; - if (!unlinked_nodes) - return -ENOMEM; - nodes_clear(*unlinked_nodes); + if (unlinked_nodes) + nodes_clear(*unlinked_nodes); sect_start_pfn = section_nr_to_pfn(phys_index); sect_end_pfn = sect_start_pfn + PAGES_PER_SECTION - 1; for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) { - int nid; + int nid = get_nid_for_pfn(pfn);; - nid = get_nid_for_pfn(pfn); if (nid < 0) continue; - if (!node_online(nid)) - continue; - if (node_test_and_set(nid, *unlinked_nodes)) + /* + * It is possible that NODEMASK_ALLOC fails due to memory pressure. + * If that happens, we fallback to call sysfs_remove_link unconditionally. + * Nothing wrong will happen as sysfs_remove_link will back off + * somewhere down the chain in case the link has already been removed. + */ + if (unlinked_nodes && node_test_and_set(nid, *unlinked_nodes)) continue; + sysfs_remove_link(&node_devices[nid]->dev.kobj, kobject_name(&mem_blk->dev.kobj)); sysfs_remove_link(&mem_blk->dev.kobj, kobject_name(&node_devices[nid]->dev.kobj)); } - NODEMASK_FREE(unlinked_nodes); - return 0; + + if (unlinked_nodes) + NODEMASK_FREE(unlinked_nodes); } int link_mem_sections(int nid, unsigned long start_pfn, unsigned long end_pfn) diff --git a/include/linux/node.h b/include/linux/node.h index 257bb3d6d014..1203378e596a 100644 --- a/include/linux/node.h +++ b/include/linux/node.h @@ -72,7 +72,7 @@ extern int register_cpu_under_node(unsigned int cpu, unsigned int nid); extern int unregister_cpu_under_node(unsigned int cpu, unsigned int nid); extern int register_mem_sect_under_node(struct memory_block *mem_blk, void *arg); -extern int unregister_mem_sect_under_nodes(struct memory_block *mem_blk, +extern void unregister_mem_sect_under_nodes(struct memory_block *mem_blk, unsigned long phys_index); #ifdef CONFIG_HUGETLBFS @@ -105,10 +105,9 @@ static inline int register_mem_sect_under_node(struct memory_block *mem_blk, { return 0; } -static inline int unregister_mem_sect_under_nodes(struct memory_block *mem_blk, +static inline void unregister_mem_sect_under_nodes(struct memory_block *mem_blk, unsigned long phys_index) { - return 0; } static inline void register_hugetlbfs_with_node(node_registration_func_t reg, -- 2.13.6