On 26.10.20 12:54, Mike Rapoport wrote:

On Mon, Oct 26, 2020 at 12:05:13PM +0100, David Hildenbrand wrote:

quoted

On 25.10.20 11:15, Mike Rapoport wrote:

quoted

From: Mike Rapoport <redacted>

When CONFIG_DEBUG_PAGEALLOC is enabled, it unmaps pages from the
kernel direct mapping after free_pages(). The pages than need to be
mapped back before they could be used. Theese mapping operations use 
__kernel_map_pages() guarded with with debug_pagealloc_enabled().

The only place that calls __kernel_map_pages() without checking
whether DEBUG_PAGEALLOC is enabled is the hibernation code that
presumes availability of this function when ARCH_HAS_SET_DIRECT_MAP
is set. Still, on arm64, __kernel_map_pages() will bail out when
DEBUG_PAGEALLOC is not enabled but set_direct_map_invalid_noflush()
may render some pages not present in the direct map and hibernation
code won't be able to save such pages.

To make page allocation debugging and hibernation interaction more
robust, the dependency on DEBUG_PAGEALLOC or ARCH_HAS_SET_DIRECT_MAP
has to be made more explicit.

Start with combining the guard condition and the call to 
__kernel_map_pages() into a single debug_pagealloc_map_pages()
function to emphasize that __kernel_map_pages() should not be called
without DEBUG_PAGEALLOC and use this new function to map/unmap pages
when page allocation debug is enabled.

As the only remaining user of kernel_map_pages() is the hibernation
code, mode that function into kernel/power/snapshot.c closer to a
caller.

s/mode/move/

quoted

Signed-off-by: Mike Rapoport <redacted> --- 
include/linux/mm.h      | 16 +++++++--------- kernel/power/snapshot.c
| 11 +++++++++++ mm/memory_hotplug.c     |  3 +-- mm/page_alloc.c
|  6 ++---- mm/slab.c               |  8 +++----- 5 files changed, 24
insertions(+), 20 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h index

ef360fe70aaf..14e397f3752c 100644 --- a/include/linux/mm.h +++
b/include/linux/mm.h @@ -2927,21 +2927,19 @@ static inline bool
debug_pagealloc_enabled_static(void) #if
defined(CONFIG_DEBUG_PAGEALLOC) ||
defined(CONFIG_ARCH_HAS_SET_DIRECT_MAP) extern void
__kernel_map_pages(struct page *page, int numpages, int enable);

-/* - * When called in DEBUG_PAGEALLOC context, the call should most
likely be - * guarded by debug_pagealloc_enabled() or
debug_pagealloc_enabled_static() - */ -static inline void 
-kernel_map_pages(struct page *page, int numpages, int enable) 
+static inline void debug_pagealloc_map_pages(struct page *page, +
int numpages, int enable) { -	__kernel_map_pages(page, numpages,
enable); +	if (debug_pagealloc_enabled_static()) +
__kernel_map_pages(page, numpages, enable); } + #ifdef
CONFIG_HIBERNATION extern bool kernel_page_present(struct page
*page); #endif	/* CONFIG_HIBERNATION */ #else	/*
CONFIG_DEBUG_PAGEALLOC || CONFIG_ARCH_HAS_SET_DIRECT_MAP */ -static
inline void -kernel_map_pages(struct page *page, int numpages, int
enable) {} +static inline void debug_pagealloc_map_pages(struct page
*page, +					     int numpages, int enable) {} #ifdef
CONFIG_HIBERNATION static inline bool kernel_page_present(struct page
*page) { return true; } #endif	/* CONFIG_HIBERNATION */ diff --git
a/kernel/power/snapshot.c b/kernel/power/snapshot.c index
46b1804c1ddf..fa499466f645 100644 --- a/kernel/power/snapshot.c +++
b/kernel/power/snapshot.c @@ -76,6 +76,17 @@ static inline void
hibernate_restore_protect_page(void *page_address) {} static inline
void hibernate_restore_unprotect_page(void *page_address) {} #endif
/* CONFIG_STRICT_KERNEL_RWX  && CONFIG_ARCH_HAS_SET_MEMORY */

+#if defined(CONFIG_DEBUG_PAGEALLOC) ||
defined(CONFIG_ARCH_HAS_SET_DIRECT_MAP) +static inline void 
+kernel_map_pages(struct page *page, int numpages, int enable) +{ +
__kernel_map_pages(page, numpages, enable); +} +#else +static inline
void +kernel_map_pages(struct page *page, int numpages, int enable)
{} +#endif +

That change should go into a separate patch.

 
Hmm, I beleive you refer to moving kernel_map_pages() to snapshot.c,
right?

Sorry, yes!


-- 
Thanks,

David / dhildenb


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