On 17.08.2018 11:00, Oscar Salvador wrote:
> From: Oscar Salvador <osalva...@suse.de>
>
> Currently, 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 kmalloc() 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.
> It is pretty rare that such a tiny allocation can fail, but if it does,
> we will be left with dangled symlinks under /sys/devices/system/node/,
> since the mem_blk's directories will be removed no matter what
> unregister_mem_sect_under_nodes() returns.
>
> One way to solve this is to check whether unlinked_nodes is NULL or not.
> In the case it is not, we can just use it as before, but if it is NULL,
> we can just skip the node_test_and_set check, and call sysfs_remove_link()
> unconditionally.
> This is harmless as sysfs_remove_link() backs off somewhere down the chain
> in case the link has already been removed.
> This method was presented in v3 of the path [1].
>
> But since the maximum number of nodes we can have is 1024,
> when NODES_SHIFT = 10, that gives us a nodemask_t of 128 bytes.
> Although everything depends on how deep the stack is, I think we can afford
> to define the nodemask_t variable whithin the stack.
>
> That simplifies the code, and we do not need to worry about untested error
> code paths.
>
> If we see that this causes troubles with the stack, we can always return to
> [1].
>
> [1] https://patchwork.kernel.org/patch/10566673/
>
> Signed-off-by: Oscar Salvador <osalva...@suse.de>
> ---
> drivers/base/node.c | 16 ++++++----------
> include/linux/node.h | 5 ++---
> 2 files changed, 8 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index dd3bdab230b2..6b8c9b4537c9 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -449,35 +449,31 @@ 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)
I am a friend of fixing up alignment of other parameters.
> {
> - NODEMASK_ALLOC(nodemask_t, unlinked_nodes, GFP_KERNEL);
> + nodemask_t unlinked_nodes;
> unsigned long pfn, sect_start_pfn, sect_end_pfn;
>
> - if (!unlinked_nodes)
> - return -ENOMEM;
> - nodes_clear(*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))
> + if (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;
> }
>
> 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);
dito
>
> #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)
dito
> {
> - return 0;
> }
>
> static inline void register_hugetlbfs_with_node(node_registration_func_t reg,
>
We'll find out if we have enough stack :) But this is definitely simpler.
--
Thanks,
David / dhildenb
