Commit db37648c authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
Browse files

[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
......@@ -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!
......
......@@ -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
......
......@@ -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;
......
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