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SubjectRe: [PATCH 1/2] mem-hotplug: Introduce {un}lock_memory_hotplug()
On Wed, 1 Dec 2010, KOSAKI Motohiro wrote:

> Now, hwpoison are using lock_system_sleep() for prevent a race
> with memory hotplug. However lock_system_sleep() is no-op if
> CONFIG_HIBERNATION=n. Therefore we need new lock.
>
> Cc: Andi Kleen <andi@firstfloor.org>
> Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Suggested-by: Hugh Dickins <hughd@google.com>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

Yes, that looks better than what I had had in mind (further abusing
pm_mutex). I notice that if MEMORY_HOTPLUG is off but HIBERNATION on,
lock_memory_hotplug does nothing where lock_system_sleep did something;
but I don't think that's a problem at all. Thanks.

Acked-by: Hugh Dickins <hughd@google.com>

> ---
> include/linux/memory_hotplug.h | 6 ++++++
> mm/memory-failure.c | 8 ++++----
> mm/memory_hotplug.c | 31 ++++++++++++++++++++++++-------
> 3 files changed, 34 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index 4307231..31c237a 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -161,6 +161,9 @@ extern void register_page_bootmem_info_node(struct pglist_data *pgdat);
> extern void put_page_bootmem(struct page *page);
> #endif
>
> +void lock_memory_hotplug(void);
> +void unlock_memory_hotplug(void);
> +
> #else /* ! CONFIG_MEMORY_HOTPLUG */
> /*
> * Stub functions for when hotplug is off
> @@ -192,6 +195,9 @@ static inline void register_page_bootmem_info_node(struct pglist_data *pgdat)
> {
> }
>
> +static inline void lock_memory_hotplug(void) {}
> +static inline void unlock_memory_hotplug(void) {}
> +
> #endif /* ! CONFIG_MEMORY_HOTPLUG */
>
> #ifdef CONFIG_MEMORY_HOTREMOVE
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 1243241..46ab2c0 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -51,6 +51,7 @@
> #include <linux/slab.h>
> #include <linux/swapops.h>
> #include <linux/hugetlb.h>
> +#include <linux/memory_hotplug.h>
> #include "internal.h"
>
> int sysctl_memory_failure_early_kill __read_mostly = 0;
> @@ -1230,11 +1231,10 @@ static int get_any_page(struct page *p, unsigned long pfn, int flags)
> return 1;
>
> /*
> - * The lock_system_sleep prevents a race with memory hotplug,
> - * because the isolation assumes there's only a single user.
> + * The lock_memory_hotplug prevents a race with memory hotplug.
> * This is a big hammer, a better would be nicer.
> */
> - lock_system_sleep();
> + lock_memory_hotplug();
>
> /*
> * Isolate the page, so that it doesn't get reallocated if it
> @@ -1264,7 +1264,7 @@ static int get_any_page(struct page *p, unsigned long pfn, int flags)
> ret = 1;
> }
> unset_migratetype_isolate(p);
> - unlock_system_sleep();
> + unlock_memory_hotplug();
> return ret;
> }
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 833e286..7549a01 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -34,6 +34,23 @@
>
> #include "internal.h"
>
> +DEFINE_MUTEX(mem_hotplug_mutex);
> +
> +void lock_memory_hotplug(void)
> +{
> + mutex_lock(&mem_hotplug_mutex);
> +
> + /* for exclusive hibernation if CONFIG_HIBERNATION=y */
> + lock_system_sleep();
> +}
> +
> +void unlock_memory_hotplug(void)
> +{
> + unlock_system_sleep();
> + mutex_unlock(&mem_hotplug_mutex);
> +}
> +
> +
> /* add this memory to iomem resource */
> static struct resource *register_memory_resource(u64 start, u64 size)
> {
> @@ -491,7 +508,7 @@ int mem_online_node(int nid)
> pg_data_t *pgdat;
> int ret;
>
> - lock_system_sleep();
> + lock_memory_hotplug();
> pgdat = hotadd_new_pgdat(nid, 0);
> if (pgdat) {
> ret = -ENOMEM;
> @@ -502,7 +519,7 @@ int mem_online_node(int nid)
> BUG_ON(ret);
>
> out:
> - unlock_system_sleep();
> + unlock_memory_hotplug();
> return ret;
> }
>
> @@ -514,7 +531,7 @@ int __ref add_memory(int nid, u64 start, u64 size)
> struct resource *res;
> int ret;
>
> - lock_system_sleep();
> + lock_memory_hotplug();
>
> res = register_memory_resource(start, size);
> ret = -EEXIST;
> @@ -561,7 +578,7 @@ error:
> release_memory_resource(res);
>
> out:
> - unlock_system_sleep();
> + unlock_memory_hotplug();
> return ret;
> }
> EXPORT_SYMBOL_GPL(add_memory);
> @@ -789,7 +806,7 @@ static int offline_pages(unsigned long start_pfn,
> if (!test_pages_in_a_zone(start_pfn, end_pfn))
> return -EINVAL;
>
> - lock_system_sleep();
> + lock_memory_hotplug();
>
> zone = page_zone(pfn_to_page(start_pfn));
> node = zone_to_nid(zone);
> @@ -877,7 +894,7 @@ repeat:
> vm_total_pages = nr_free_pagecache_pages();
>
> memory_notify(MEM_OFFLINE, &arg);
> - unlock_system_sleep();
> + unlock_memory_hotplug();
> return 0;
>
> failed_removal:
> @@ -888,7 +905,7 @@ failed_removal:
> undo_isolate_page_range(start_pfn, end_pfn);
>
> out:
> - unlock_system_sleep();
> + unlock_memory_hotplug();
> return ret;
> }
>
> --
> 1.6.5.2


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