mm: protect set_page_dirty() from ongoing truncation
Tejun, while reviewing the code, spotted the following race condition
between the dirtying and truncation of a page:
__set_page_dirty_nobuffers() __delete_from_page_cache()
if (TestSetPageDirty(page))
page->mapping = NULL
if (PageDirty())
dec_zone_page_state(page, NR_FILE_DIRTY);
dec_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
if (page->mapping)
account_page_dirtied(page)
__inc_zone_page_state(page, NR_FILE_DIRTY);
__inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
which results in an imbalance of NR_FILE_DIRTY and BDI_RECLAIMABLE.
Dirtiers usually lock out truncation, either by holding the page lock
directly, or in case of zap_pte_range(), by pinning the mapcount with
the page table lock held. The notable exception to this rule, though,
is do_wp_page(), for which this race exists. However, do_wp_page()
already waits for a locked page to unlock before setting the dirty bit,
in order to prevent a race where clear_page_dirty() misses the page bit
in the presence of dirty ptes. Upgrade that wait to a fully locked
set_page_dirty() to also cover the situation explained above.
Afterwards, the code in set_page_dirty() dealing with a truncation race
is no longer needed. Remove it.
Reported-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index d5d81f5..6f43352 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1541,16 +1541,6 @@
bdi_start_background_writeback(bdi);
}
-void set_page_dirty_balance(struct page *page)
-{
- if (set_page_dirty(page)) {
- struct address_space *mapping = page_mapping(page);
-
- if (mapping)
- balance_dirty_pages_ratelimited(mapping);
- }
-}
-
static DEFINE_PER_CPU(int, bdp_ratelimits);
/*
@@ -2123,32 +2113,25 @@
* page dirty in that case, but not all the buffers. This is a "bottom-up"
* dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
*
- * Most callers have locked the page, which pins the address_space in memory.
- * But zap_pte_range() does not lock the page, however in that case the
- * mapping is pinned by the vma's ->vm_file reference.
- *
- * We take care to handle the case where the page was truncated from the
- * mapping by re-checking page_mapping() inside tree_lock.
+ * The caller must ensure this doesn't race with truncation. Most will simply
+ * hold the page lock, but e.g. zap_pte_range() calls with the page mapped and
+ * the pte lock held, which also locks out truncation.
*/
int __set_page_dirty_nobuffers(struct page *page)
{
if (!TestSetPageDirty(page)) {
struct address_space *mapping = page_mapping(page);
- struct address_space *mapping2;
unsigned long flags;
if (!mapping)
return 1;
spin_lock_irqsave(&mapping->tree_lock, flags);
- mapping2 = page_mapping(page);
- if (mapping2) { /* Race with truncate? */
- BUG_ON(mapping2 != mapping);
- WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
- account_page_dirtied(page, mapping);
- radix_tree_tag_set(&mapping->page_tree,
- page_index(page), PAGECACHE_TAG_DIRTY);
- }
+ BUG_ON(page_mapping(page) != mapping);
+ WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page));
+ account_page_dirtied(page, mapping);
+ radix_tree_tag_set(&mapping->page_tree, page_index(page),
+ PAGECACHE_TAG_DIRTY);
spin_unlock_irqrestore(&mapping->tree_lock, flags);
if (mapping->host) {
/* !PageAnon && !swapper_space */
@@ -2305,12 +2288,10 @@
/*
* We carefully synchronise fault handlers against
* installing a dirty pte and marking the page dirty
- * at this point. We do this by having them hold the
- * page lock at some point after installing their
- * pte, but before marking the page dirty.
- * Pages are always locked coming in here, so we get
- * the desired exclusion. See mm/memory.c:do_wp_page()
- * for more comments.
+ * at this point. We do this by having them hold the
+ * page lock while dirtying the page, and pages are
+ * always locked coming in here, so we get the desired
+ * exclusion.
*/
if (TestClearPageDirty(page)) {
dec_zone_page_state(page, NR_FILE_DIRTY);