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Commit c97a9e10 authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
Browse files

mm: more rmap checking 



Re-introduce rmap verification patches that Hugh removed when he removed
PG_map_lock. PG_map_lock actually isn't needed to synchronise access to
anonymous pages, because PG_locked and PTL together already do.

These checks were important in discovering and fixing a rare rmap corruption
in SLES9.

Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ea125892

include/linux/rmap.h

+5 −8
Original line number Diff line number Diff line
@@ -74,17 +74,14 @@ void page_add_new_anon_rmap(struct page *, struct vm_area_struct *, unsigned lon 
void page_add_file_rmap(struct page *);

void page_remove_rmap(struct page *, struct vm_area_struct *);



/**

 * page_dup_rmap - duplicate pte mapping to a page

 * @page:	the page to add the mapping to

 *

 * For copy_page_range only: minimal extract from page_add_rmap,

 * avoiding unnecessary tests (already checked) so it's quicker.

 */

static inline void page_dup_rmap(struct page *page)

#ifdef CONFIG_DEBUG_VM

void page_dup_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address);

#else

static inline void page_dup_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address)

{

	atomic_inc(&page->_mapcount);

}

#endif



/*

 * Called from mm/vmscan.c to handle paging out

mm/memory.c

+1 −1
Original line number Diff line number Diff line
@@ -481,7 +481,7 @@ copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm, 
	page = vm_normal_page(vma, addr, pte);

	if (page) {

		get_page(page);

		page_dup_rmap(page);

		page_dup_rmap(page, vma, addr);

		rss[!!PageAnon(page)]++;

	}

mm/rmap.c

+56 −2
Original line number Diff line number Diff line
@@ -529,20 +529,52 @@ static void __page_set_anon_rmap(struct page *page, 
	__inc_zone_page_state(page, NR_ANON_PAGES);

}



/**

 * page_set_anon_rmap - sanity check anonymous rmap addition

 * @page:	the page to add the mapping to

 * @vma:	the vm area in which the mapping is added

 * @address:	the user virtual address mapped

 */

static void __page_check_anon_rmap(struct page *page,

	struct vm_area_struct *vma, unsigned long address)

{

#ifdef CONFIG_DEBUG_VM

	/*

	 * The page's anon-rmap details (mapping and index) are guaranteed to

	 * be set up correctly at this point.

	 *

	 * We have exclusion against page_add_anon_rmap because the caller

	 * always holds the page locked, except if called from page_dup_rmap,

	 * in which case the page is already known to be setup.

	 *

	 * We have exclusion against page_add_new_anon_rmap because those pages

	 * are initially only visible via the pagetables, and the pte is locked

	 * over the call to page_add_new_anon_rmap.

	 */

	struct anon_vma *anon_vma = vma->anon_vma;

	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;

	BUG_ON(page->mapping != (struct address_space *)anon_vma);

	BUG_ON(page->index != linear_page_index(vma, address));

#endif

}



/**

 * page_add_anon_rmap - add pte mapping to an anonymous page

 * @page:	the page to add the mapping to

 * @vma:	the vm area in which the mapping is added

 * @address:	the user virtual address mapped

 *

 * The caller needs to hold the pte lock.

 * The caller needs to hold the pte lock and the page must be locked.

 */

void page_add_anon_rmap(struct page *page,

	struct vm_area_struct *vma, unsigned long address)

{

	VM_BUG_ON(!PageLocked(page));

	VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);

	if (atomic_inc_and_test(&page->_mapcount))

		__page_set_anon_rmap(page, vma, address);

	/* else checking page index and mapping is racy */

	else

		__page_check_anon_rmap(page, vma, address);

}



/*
@@ -553,10 +585,12 @@ void page_add_anon_rmap(struct page *page, 
 *

 * Same as page_add_anon_rmap but must only be called on *new* pages.

 * This means the inc-and-test can be bypassed.

 * Page does not have to be locked.

 */

void page_add_new_anon_rmap(struct page *page,

	struct vm_area_struct *vma, unsigned long address)

{

	BUG_ON(address < vma->vm_start || address >= vma->vm_end);

	atomic_set(&page->_mapcount, 0); /* elevate count by 1 (starts at -1) */

	__page_set_anon_rmap(page, vma, address);

}
@@ -573,6 +607,26 @@ void page_add_file_rmap(struct page *page) 
		__inc_zone_page_state(page, NR_FILE_MAPPED);

}



#ifdef CONFIG_DEBUG_VM

/**

 * page_dup_rmap - duplicate pte mapping to a page

 * @page:	the page to add the mapping to

 *

 * For copy_page_range only: minimal extract from page_add_file_rmap /

 * page_add_anon_rmap, avoiding unnecessary tests (already checked) so it's

 * quicker.

 *

 * The caller needs to hold the pte lock.

 */

void page_dup_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address)

{

	BUG_ON(page_mapcount(page) == 0);

	if (PageAnon(page))

		__page_check_anon_rmap(page, vma, address);

	atomic_inc(&page->_mapcount);

}

#endif



/**

 * page_remove_rmap - take down pte mapping from a page

 * @page: page to remove mapping from