Re: [PATCH 3/3] mm: don't panic when links can't be created in sysfs

Michal Hocko
2020-09-14T08:59:11Z

On Fri 11-09-20 15:48:31, Laurent Dufour wrote:
> At boot time, or when doing memory hot-add operations, if the links in
> sysfs can't be created, the system is still able to run, so just report the
> error in the kernel log.

.. rather than BUG_ON and potentially make system unusable because the
callpath can be called with locks held etc...

> Since the number of memory blocks managed could be high, the messages are
> rate limited.
>
> As a consequence, link_mem_sections() has no status to report anymore.
>
> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
> Cc: David Hildenbrand <david@redhat.com>

Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!

> ---
> drivers/base/node.c | 25 +++++++++++++++++--------
> include/linux/node.h | 17 ++++++++---------
> mm/memory_hotplug.c | 5 ++---
> 3 files changed, 27 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 862516c5a5ae..749a1c8ea992 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -811,12 +811,21 @@ static int register_mem_sect_under_node(struct memory_block *mem_blk,
> ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
> &mem_blk->dev.kobj,
> kobject_name(&mem_blk->dev.kobj));
> - if (ret)
> - return ret;
> + if (ret && ret != -EEXIST)
> + pr_err_ratelimited(
> + "can't create %s to %s link in sysfs (%d)\n",
> + kobject_name(&node_devices[nid]->dev.kobj),
> + kobject_name(&mem_blk->dev.kobj), ret);
>
> - return sysfs_create_link_nowarn(&mem_blk->dev.kobj,
> + ret = sysfs_create_link_nowarn(&mem_blk->dev.kobj,
> &node_devices[nid]->dev.kobj,
> kobject_name(&node_devices[nid]->dev.kobj));
> + if (ret && ret != -EEXIST)
> + pr_err_ratelimited(
> + "can't create %s to %s link in sysfs (%d)\n",
> + kobject_name(&mem_blk->dev.kobj),
> + kobject_name(&node_devices[nid]->dev.kobj),
> + ret);
> }
> /* mem section does not span the specified node */
> return 0;
> @@ -837,17 +846,17 @@ void unregister_memory_block_under_nodes(struct memory_block *mem_blk)
> kobject_name(&node_devices[mem_blk->nid]->dev.kobj));
> }
>
> -int link_mem_sections(int nid, unsigned long start_pfn, unsigned long end_pfn,
> - enum memplug_context context)
> +void link_mem_sections(int nid, unsigned long start_pfn, unsigned long end_pfn,
> + enum memplug_context context)
> {
> struct rmsun_args args = {
> .nid = nid,
> .context = context,
> };
>
> - return walk_memory_blocks(PFN_PHYS(start_pfn),
> - PFN_PHYS(end_pfn - start_pfn), (void *)&args,
> - register_mem_sect_under_node);
> + walk_memory_blocks(PFN_PHYS(start_pfn),
> + PFN_PHYS(end_pfn - start_pfn), (void *)&args,
> + register_mem_sect_under_node);
> }
>
> #ifdef CONFIG_HUGETLBFS
> diff --git a/include/linux/node.h b/include/linux/node.h
> index 8ff08520488c..6bdd6f3ed3aa 100644
> --- a/include/linux/node.h
> +++ b/include/linux/node.h
> @@ -99,15 +99,14 @@ extern struct node *node_devices[];
> typedef void (*node_registration_func_t)(struct node *);
>
> #if defined(CONFIG_MEMORY_HOTPLUG_SPARSE) && defined(CONFIG_NUMA)
> -extern int link_mem_sections(int nid, unsigned long start_pfn,
> - unsigned long end_pfn,
> - enum memplug_context context);
> +void link_mem_sections(int nid, unsigned long start_pfn,
> + unsigned long end_pfn,
> + enum memplug_context context);
> #else
> -static inline int link_mem_sections(int nid, unsigned long start_pfn,
> - unsigned long end_pfn,
> - enum memplug_context context)
> +static inline void link_mem_sections(int nid, unsigned long start_pfn,
> + unsigned long end_pfn,
> + enum memplug_context context)
> {
> - return 0;
> }
> #endif
>
> @@ -130,8 +129,8 @@ static inline int register_one_node(int nid)
> if (error)
> return error;
> /* link memory sections under this node */
> - error = link_mem_sections(nid, start_pfn, end_pfn,
> - MEMPLUG_EARLY);
> + link_mem_sections(nid, start_pfn, end_pfn,
> + MEMPLUG_EARLY);
> }
>
> return error;
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 912d355ca446..668418071a49 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1080,9 +1080,8 @@ int __ref add_memory_resource(int nid, struct resource *res)
> }
>
> /* link memory sections under this node.*/
> - ret = link_mem_sections(nid, PFN_DOWN(start), PFN_UP(start + size - 1),
> - MEMPLUG_HOTPLUG);
> - BUG_ON(ret);
> + link_mem_sections(nid, PFN_DOWN(start), PFN_UP(start + size - 1),
> + MEMPLUG_HOTPLUG);
>
> /* create new memmap entry */
> if (!strcmp(res->name, "System RAM"))
> --
> 2.28.0

--
Michal Hocko
SUSE Labs