From: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Subject: x86/mm: set fields in deferred pages
Without deferred struct page feature (CONFIG_DEFERRED_STRUCT_PAGE_INIT),
flags and other fields in "struct page"es are never changed prior to first
initializing struct pages by going through __init_single_page().
With deferred struct page feature enabled, however, we set fields in
register_page_bootmem_info that are subsequently clobbered right after in
free_all_bootmem:
mem_init() {
register_page_bootmem_info();
free_all_bootmem();
...
}
When register_page_bootmem_info() is called only non-deferred struct pages
are initialized. But, this function goes through some reserved pages
which might be part of the deferred, and thus are not yet initialized.
mem_init
register_page_bootmem_info
register_page_bootmem_info_node
get_page_bootmem
.. setting fields here ..
such as: page->freelist = (void *)type;
free_all_bootmem()
free_low_memory_core_early()
for_each_reserved_mem_region()
reserve_bootmem_region()
init_reserved_page() <- Only if this is deferred reserved page
__init_single_pfn()
__init_single_page()
memset(0) <-- Loose the set fields here
We end up with issue where, currently we do not observe problem as memory
is explicitly zeroed. But, if flag asserts are changed we can start
hitting issues.
Also, because in this patch series we will stop zeroing struct page memory
during allocation, we must make sure that struct pages are properly
initialized prior to using them.
The deferred-reserved pages are initialized in free_all_bootmem().
Therefore, the fix is to switch the above calls.
Link: http://lkml.kernel.org/r/20171013173214.27300-3-pasha.tatashin@xxxxxxxxxx
Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Reviewed-by: Steven Sistare <steven.sistare@xxxxxxxxxx>
Reviewed-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Reviewed-by: Bob Picco <bob.picco@xxxxxxxxxx>
Tested-by: Bob Picco <bob.picco@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Sam Ravnborg <sam@xxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/x86/mm/init_64.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff -puN arch/x86/mm/init_64.c~x86-mm-setting-fields-in-deferred-pages arch/x86/mm/init_64.c
--- a/arch/x86/mm/init_64.c~x86-mm-setting-fields-in-deferred-pages
+++ a/arch/x86/mm/init_64.c
@@ -1173,12 +1173,18 @@ void __init mem_init(void)
/* clear_bss() already clear the empty_zero_page */
- register_page_bootmem_info();
-
/* this will put all memory onto the freelists */
free_all_bootmem();
after_bootmem = 1;
+ /*
+ * Must be done after boot memory is put on freelist, because here we
+ * might set fields in deferred struct pages that have not yet been
+ * initialized, and free_all_bootmem() initializes all the reserved
+ * deferred pages for us.
+ */
+ register_page_bootmem_info();
+
/* Register memory areas for /proc/kcore */
kclist_add(&kcore_vsyscall, (void *)VSYSCALL_ADDR,
PAGE_SIZE, KCORE_OTHER);
_
--
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