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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: Nick Piggin <npiggin@suse.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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28e4d965e6
commit
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3 changed files with 33 additions and 1 deletions
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@ -130,14 +130,29 @@ static inline pgoff_t linear_page_index(struct vm_area_struct *vma,
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}
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extern void FASTCALL(__lock_page(struct page *page));
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extern void FASTCALL(__lock_page_nosync(struct page *page));
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extern void FASTCALL(unlock_page(struct page *page));
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/*
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* lock_page may only be called if we have the page's inode pinned.
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*/
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static inline void lock_page(struct page *page)
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{
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might_sleep();
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if (TestSetPageLocked(page))
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__lock_page(page);
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}
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/*
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* lock_page_nosync should only be used if we can't pin the page's inode.
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* Doesn't play quite so well with block device plugging.
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*/
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static inline void lock_page_nosync(struct page *page)
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{
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might_sleep();
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if (TestSetPageLocked(page))
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__lock_page_nosync(page);
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}
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/*
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* This is exported only for wait_on_page_locked/wait_on_page_writeback.
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17
mm/filemap.c
17
mm/filemap.c
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@ -488,6 +488,12 @@ struct page *page_cache_alloc_cold(struct address_space *x)
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EXPORT_SYMBOL(page_cache_alloc_cold);
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#endif
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static int __sleep_on_page_lock(void *word)
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{
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io_schedule();
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return 0;
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}
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/*
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* In order to wait for pages to become available there must be
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* waitqueues associated with pages. By using a hash table of
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@ -577,6 +583,17 @@ void fastcall __lock_page(struct page *page)
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}
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EXPORT_SYMBOL(__lock_page);
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/*
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* Variant of lock_page that does not require the caller to hold a reference
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* on the page's mapping.
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*/
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void fastcall __lock_page_nosync(struct page *page)
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{
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DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
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__wait_on_bit_lock(page_waitqueue(page), &wait, __sleep_on_page_lock,
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TASK_UNINTERRUPTIBLE);
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}
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/**
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* find_get_page - find and get a page reference
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* @mapping: the address_space to search
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@ -701,7 +701,7 @@ int set_page_dirty_lock(struct page *page)
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{
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int ret;
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lock_page(page);
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lock_page_nosync(page);
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ret = set_page_dirty(page);
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unlock_page(page);
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return ret;
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