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authorNick Piggin <npiggin@suse.de>2006-09-25 23:31:24 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-09-26 08:48:48 -0700
commitdb37648cd6ce9b828abd6d49aa3d269926ee7b7d (patch)
treea0155c7897f4706386d10c8718f98687bc357c82
parent28e4d965e6131ace1e813e93aebca89ac6b82dc1 (diff)
[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>
-rw-r--r--include/linux/pagemap.h15
-rw-r--r--mm/filemap.c17
-rw-r--r--mm/page-writeback.c2
3 files changed, 33 insertions, 1 deletions
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 0a2f5d27f60..64f95092515 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -130,14 +130,29 @@ 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();
if (TestSetPageLocked(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.
diff --git a/mm/filemap.c b/mm/filemap.c
index b9a60c43b61..d5af1cab426 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -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
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index b9f4c6f1be8..555752907dc 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -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;