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Commit db37648c authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
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[PATCH] mm: non syncing lock_page() 



lock_page needs the caller to have a reference on the page->mapping inode
due to sync_page, ergo set_page_dirty_lock is obviously buggy according to
its comments.

Solve it by introducing a new lock_page_nosync which does not do a sync_page.

akpm: unpleasant solution to an unpleasant problem.  If it goes wrong it could
cause great slowdowns while the lock_page() caller waits for kblockd to
perform the unplug.  And if a filesystem has special sync_page() requirements
(none presently do), permanent hangs are possible.

otoh, set_page_dirty_lock() is usually (always?) called against userspace
pages.  They are always up-to-date, so there shouldn't be any pending read I/O
against these pages.

Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 28e4d965

include/linux/pagemap.h

+15 −0
Original line number Diff line number Diff line
@@ -130,8 +130,12 @@ static inline pgoff_t linear_page_index(struct vm_area_struct *vma, 
}



extern void FASTCALL(__lock_page(struct page *page));

extern void FASTCALL(__lock_page_nosync(struct page *page));

extern void FASTCALL(unlock_page(struct page *page));



/*

 * lock_page may only be called if we have the page's inode pinned.

 */

static inline void lock_page(struct page *page)

{

	might_sleep();
@@ -139,6 +143,17 @@ static inline void lock_page(struct page *page) 
		__lock_page(page);

}



/*

 * lock_page_nosync should only be used if we can't pin the page's inode.

 * Doesn't play quite so well with block device plugging.

 */

static inline void lock_page_nosync(struct page *page)

{

	might_sleep();

	if (TestSetPageLocked(page))

		__lock_page_nosync(page);

}

	

/*

 * This is exported only for wait_on_page_locked/wait_on_page_writeback.

 * Never use this directly!

mm/filemap.c

+17 −0
Original line number Diff line number Diff line
@@ -488,6 +488,12 @@ struct page *page_cache_alloc_cold(struct address_space *x) 
EXPORT_SYMBOL(page_cache_alloc_cold);

#endif



static int __sleep_on_page_lock(void *word)

{

	io_schedule();

	return 0;

}



/*

 * In order to wait for pages to become available there must be

 * waitqueues associated with pages. By using a hash table of
@@ -577,6 +583,17 @@ void fastcall __lock_page(struct page *page) 
}

EXPORT_SYMBOL(__lock_page);



/*

 * Variant of lock_page that does not require the caller to hold a reference

 * on the page's mapping.

 */

void fastcall __lock_page_nosync(struct page *page)

{

	DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);

	__wait_on_bit_lock(page_waitqueue(page), &wait, __sleep_on_page_lock,

							TASK_UNINTERRUPTIBLE);

}



/**

 * find_get_page - find and get a page reference

 * @mapping: the address_space to search

mm/page-writeback.c

+1 −1
Original line number Diff line number Diff line
@@ -701,7 +701,7 @@ int set_page_dirty_lock(struct page *page) 
{

	int ret;



	lock_page(page);

	lock_page_nosync(page);

	ret = set_page_dirty(page);

	unlock_page(page);

	return ret;