| Message ID | 20180813154639.19454-4-osalvador@techadventures.net (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Refactoring for remove_memory_section/unregister_mem_sect_under_nodes | expand |
On 13.08.2018 17:46, osalvador@techadventures.net wrote: > From: Oscar Salvador <osalvador@suse.de> > > 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. I would prefer splitting this change out into a separate patch. > > 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 <osalvador@suse.de> > --- > 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); NODEMASK_FEEE/kfree can deal with NULL pointers. > } > > 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, >
On Tue, Aug 14, 2018 at 11:39:34AM +0200, David Hildenbrand wrote: > On 13.08.2018 17:46, osalvador@techadventures.net wrote: > > From: Oscar Salvador <osalvador@suse.de> > > 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. > > I would prefer splitting this change out into a separate patch. Yes, I guess it is better as it is not really related to the changes in this patch. I will wait for more feedback and I will split it up in v3. > > + > > + if (unlinked_nodes) > > + NODEMASK_FREE(unlinked_nodes); > > NODEMASK_FEEE/kfree can deal with NULL pointers. Good point, I missed that. I will fix it up in v3. Thanks for reviewing.
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,