Patch "sparc64/mm: set fields in deferred pages" has been added to the 3.18-stable tree

This is a note to let you know that I've just added the patch titled

sparc64/mm: set fields in deferred pages

to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
sparc64-mm-set-fields-in-deferred-pages.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Pavel Tatashin <[email protected]>
Date: Wed, 15 Nov 2017 17:36:18 -0800
Subject: sparc64/mm: set fields in deferred pages

From: Pavel Tatashin <[email protected]>

[ Upstream commit 2a20aa171071a334d80c4e5d5af719d8374702fc ]

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 there is a case where we set some fields prior to initializing:

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 similar issue as in the previous patch, where currently we do not observe problem as memory is 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.

---
 arch/sparc/mm/init_64.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

@@ -2215,10 +2215,17 @@ void __init mem_init(void)
 {
 	high_memory = __va(last_valid_pfn << PAGE_SHIFT);
 
-	register_page_bootmem_info();
 	free_all_bootmem();
 
 	/*
+	 * 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();
+
+	/*
 	 * Set up the zero page, mark it reserved, so that page count
 	 * is not manipulated when freeing the page from user ptes.
 	 */

Patches currently in stable-queue which might be from [email protected] are

queue-3.18/sparc64-mm-set-fields-in-deferred-pages.patch