1 files changed, 173 insertions, 71 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 1aaea26556cc..38546dca58fe 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -414,7 +414,7 @@ int __filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
 		.range_end = end,
 	};
 
-	if (!mapping_cap_writeback_dirty(mapping) ||
+	if (!mapping_can_writeback(mapping) ||
 	    !mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
 		return 0;
 
@@ -988,9 +988,43 @@ void __init pagecache_init(void)
 	page_writeback_init();
 }
 
+/*
+ * The page wait code treats the "wait->flags" somewhat unusually, because
+ * we have multiple different kinds of waits, not just the usual "exclusive"
+ * one.
+ *
+ * We have:
+ *
+ *  (a) no special bits set:
+ *
+ *	We're just waiting for the bit to be released, and when a waker
+ *	calls the wakeup function, we set WQ_FLAG_WOKEN and wake it up,
+ *	and remove it from the wait queue.
+ *
+ *	Simple and straightforward.
+ *
+ *  (b) WQ_FLAG_EXCLUSIVE:
+ *
+ *	The waiter is waiting to get the lock, and only one waiter should
+ *	be woken up to avoid any thundering herd behavior. We'll set the
+ *	WQ_FLAG_WOKEN bit, wake it up, and remove it from the wait queue.
+ *
+ *	This is the traditional exclusive wait.
+ *
+ *  (c) WQ_FLAG_EXCLUSIVE | WQ_FLAG_CUSTOM:
+ *
+ *	The waiter is waiting to get the bit, and additionally wants the
+ *	lock to be transferred to it for fair lock behavior. If the lock
+ *	cannot be taken, we stop walking the wait queue without waking
+ *	the waiter.
+ *
+ *	This is the "fair lock handoff" case, and in addition to setting
+ *	WQ_FLAG_WOKEN, we set WQ_FLAG_DONE to let the waiter easily see
+ *	that it now has the lock.
+ */
 static int wake_page_function(wait_queue_entry_t *wait, unsigned mode, int sync, void *arg)
 {
-	int ret;
+	unsigned int flags;
 	struct wait_page_key *key = arg;
 	struct wait_page_queue *wait_page
 		= container_of(wait, struct wait_page_queue, wait);
@@ -999,35 +1033,44 @@ static int wake_page_function(wait_queue_entry_t *wait, unsigned mode, int sync,
 		return 0;
 
 	/*
-	 * If it's an exclusive wait, we get the bit for it, and
-	 * stop walking if we can't.
-	 *
-	 * If it's a non-exclusive wait, then the fact that this
-	 * wake function was called means that the bit already
-	 * was cleared, and we don't care if somebody then
-	 * re-took it.
+	 * If it's a lock handoff wait, we get the bit for it, and
+	 * stop walking (and do not wake it up) if we can't.
 	 */
-	ret = 0;
-	if (wait->flags & WQ_FLAG_EXCLUSIVE) {
-		if (test_and_set_bit(key->bit_nr, &key->page->flags))
+	flags = wait->flags;
+	if (flags & WQ_FLAG_EXCLUSIVE) {
+		if (test_bit(key->bit_nr, &key->page->flags))
 			return -1;
-		ret = 1;
+		if (flags & WQ_FLAG_CUSTOM) {
+			if (test_and_set_bit(key->bit_nr, &key->page->flags))
+				return -1;
+			flags |= WQ_FLAG_DONE;
+		}
 	}
-	wait->flags |= WQ_FLAG_WOKEN;
 
+	/*
+	 * We are holding the wait-queue lock, but the waiter that
+	 * is waiting for this will be checking the flags without
+	 * any locking.
+	 *
+	 * So update the flags atomically, and wake up the waiter
+	 * afterwards to avoid any races. This store-release pairs
+	 * with the load-acquire in wait_on_page_bit_common().
+	 */
+	smp_store_release(&wait->flags, flags | WQ_FLAG_WOKEN);
 	wake_up_state(wait->private, mode);
 
 	/*
 	 * Ok, we have successfully done what we're waiting for,
 	 * and we can unconditionally remove the wait entry.
 	 *
-	 * Note that this has to be the absolute last thing we do,
-	 * since after list_del_init(&wait->entry) the wait entry
+	 * Note that this pairs with the "finish_wait()" in the
+	 * waiter, and has to be the absolute last thing we do.
+	 * After this list_del_init(&wait->entry) the wait entry
 	 * might be de-allocated and the process might even have
 	 * exited.
 	 */
 	list_del_init_careful(&wait->entry);
-	return ret;
+	return (flags & WQ_FLAG_EXCLUSIVE) != 0;
 }
 
 static void wake_up_page_bit(struct page *page, int bit_nr)
@@ -1107,8 +1150,8 @@ enum behavior {
 };
 
 /*
- * Attempt to check (or get) the page bit, and mark the
- * waiter woken if successful.
+ * Attempt to check (or get) the page bit, and mark us done
+ * if successful.
  */
 static inline bool trylock_page_bit_common(struct page *page, int bit_nr,
 					struct wait_queue_entry *wait)
@@ -1119,13 +1162,17 @@ static inline bool trylock_page_bit_common(struct page *page, int bit_nr,
 	} else if (test_bit(bit_nr, &page->flags))
 		return false;
 
-	wait->flags |= WQ_FLAG_WOKEN;
+	wait->flags |= WQ_FLAG_WOKEN | WQ_FLAG_DONE;
 	return true;
 }
 
+/* How many times do we accept lock stealing from under a waiter? */
+int sysctl_page_lock_unfairness = 5;
+
 static inline int wait_on_page_bit_common(wait_queue_head_t *q,
 	struct page *page, int bit_nr, int state, enum behavior behavior)
 {
+	int unfairness = sysctl_page_lock_unfairness;
 	struct wait_page_queue wait_page;
 	wait_queue_entry_t *wait = &wait_page.wait;
 	bool thrashing = false;
@@ -1143,11 +1190,18 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
 	}
 
 	init_wait(wait);
-	wait->flags = behavior == EXCLUSIVE ? WQ_FLAG_EXCLUSIVE : 0;
 	wait->func = wake_page_function;
 	wait_page.page = page;
 	wait_page.bit_nr = bit_nr;
 
+repeat:
+	wait->flags = 0;
+	if (behavior == EXCLUSIVE) {
+		wait->flags = WQ_FLAG_EXCLUSIVE;
+		if (--unfairness < 0)
+			wait->flags |= WQ_FLAG_CUSTOM;
+	}
+
 	/*
 	 * Do one last check whether we can get the
 	 * page bit synchronously.
@@ -1170,27 +1224,63 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
 
 	/*
 	 * From now on, all the logic will be based on
-	 * the WQ_FLAG_WOKEN flag, and the and the page
-	 * bit testing (and setting) will be - or has
-	 * already been - done by the wake function.
+	 * the WQ_FLAG_WOKEN and WQ_FLAG_DONE flag, to
+	 * see whether the page bit testing has already
+	 * been done by the wake function.
 	 *
 	 * We can drop our reference to the page.
 	 */
 	if (behavior == DROP)
 		put_page(page);
 
+	/*
+	 * Note that until the "finish_wait()", or until
+	 * we see the WQ_FLAG_WOKEN flag, we need to
+	 * be very careful with the 'wait->flags', because
+	 * we may race with a waker that sets them.
+	 */
 	for (;;) {
+		unsigned int flags;
+
 		set_current_state(state);
 
-		if (signal_pending_state(state, current))
+		/* Loop until we've been woken or interrupted */
+		flags = smp_load_acquire(&wait->flags);
+		if (!(flags & WQ_FLAG_WOKEN)) {
+			if (signal_pending_state(state, current))
+				break;
+
+			io_schedule();
+			continue;
+		}
+
+		/* If we were non-exclusive, we're done */
+		if (behavior != EXCLUSIVE)
 			break;
 
-		if (wait->flags & WQ_FLAG_WOKEN)
+		/* If the waker got the lock for us, we're done */
+		if (flags & WQ_FLAG_DONE)
 			break;
 
-		io_schedule();
+		/*
+		 * Otherwise, if we're getting the lock, we need to
+		 * try to get it ourselves.
+		 *
+		 * And if that fails, we'll have to retry this all.
+		 */
+		if (unlikely(test_and_set_bit(bit_nr, &page->flags)))
+			goto repeat;
+
+		wait->flags |= WQ_FLAG_DONE;
+		break;
 	}
 
+	/*
+	 * If a signal happened, this 'finish_wait()' may remove the last
+	 * waiter from the wait-queues, but the PageWaiters bit will remain
+	 * set. That's ok. The next wakeup will take care of it, and trying
+	 * to do it here would be difficult and prone to races.
+	 */
 	finish_wait(q, wait);
 
 	if (thrashing) {
@@ -1200,12 +1290,20 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
 	}
 
 	/*
-	 * A signal could leave PageWaiters set. Clearing it here if
-	 * !waitqueue_active would be possible (by open-coding finish_wait),
-	 * but still fail to catch it in the case of wait hash collision. We
-	 * already can fail to clear wait hash collision cases, so don't
-	 * bother with signals either.
+	 * NOTE! The wait->flags weren't stable until we've done the
+	 * 'finish_wait()', and we could have exited the loop above due
+	 * to a signal, and had a wakeup event happen after the signal
+	 * test but before the 'finish_wait()'.
+	 *
+	 * So only after the finish_wait() can we reliably determine
+	 * if we got woken up or not, so we can now figure out the final
+	 * return value based on that state without races.
+	 *
+	 * Also note that WQ_FLAG_WOKEN is sufficient for a non-exclusive
+	 * waiter, but an exclusive one requires WQ_FLAG_DONE.
 	 */
+	if (behavior == EXCLUSIVE)
+		return wait->flags & WQ_FLAG_DONE ? 0 : -EINTR;
 
 	return wait->flags & WQ_FLAG_WOKEN ? 0 : -EINTR;
 }
@@ -1547,19 +1645,19 @@ EXPORT_SYMBOL(page_cache_prev_miss);
 /**
  * find_get_entry - find and get a page cache entry
  * @mapping: the address_space to search
- * @offset: the page cache index
+ * @index: The page cache index.
  *
  * Looks up the page cache slot at @mapping & @offset.  If there is a
- * page cache page, it is returned with an increased refcount.
+ * page cache page, the head page is returned with an increased refcount.
  *
  * If the slot holds a shadow entry of a previously evicted page, or a
  * swap entry from shmem/tmpfs, it is returned.
  *
- * Return: the found page or shadow entry, %NULL if nothing is found.
+ * Return: The head page or shadow entry, %NULL if nothing is found.
  */
-struct page *find_get_entry(struct address_space *mapping, pgoff_t offset)
+struct page *find_get_entry(struct address_space *mapping, pgoff_t index)
 {
-	XA_STATE(xas, &mapping->i_pages, offset);
+	XA_STATE(xas, &mapping->i_pages, index);
 	struct page *page;
 
 	rcu_read_lock();
@@ -1587,7 +1685,6 @@ repeat:
 		put_page(page);
 		goto repeat;
 	}
-	page = find_subpage(page, offset);
 out:
 	rcu_read_unlock();
 
@@ -1595,40 +1692,37 @@ out:
 }
 
 /**
- * find_lock_entry - locate, pin and lock a page cache entry
- * @mapping: the address_space to search
- * @offset: the page cache index
+ * find_lock_entry - Locate and lock a page cache entry.
+ * @mapping: The address_space to search.
+ * @index: The page cache index.
  *
- * Looks up the page cache slot at @mapping & @offset.  If there is a
- * page cache page, it is returned locked and with an increased
- * refcount.
+ * Looks up the page at @mapping & @index.  If there is a page in the
+ * cache, the head page is returned locked and with an increased refcount.
  *
  * If the slot holds a shadow entry of a previously evicted page, or a
  * swap entry from shmem/tmpfs, it is returned.
  *
- * find_lock_entry() may sleep.
- *
- * Return: the found page or shadow entry, %NULL if nothing is found.
+ * Context: May sleep.
+ * Return: The head page or shadow entry, %NULL if nothing is found.
  */
-struct page *find_lock_entry(struct address_space *mapping, pgoff_t offset)
+struct page *find_lock_entry(struct address_space *mapping, pgoff_t index)
 {
 	struct page *page;
 
 repeat:
-	page = find_get_entry(mapping, offset);
+	page = find_get_entry(mapping, index);
 	if (page && !xa_is_value(page)) {
 		lock_page(page);
 		/* Has the page been truncated? */
-		if (unlikely(page_mapping(page) != mapping)) {
+		if (unlikely(page->mapping != mapping)) {
 			unlock_page(page);
 			put_page(page);
 			goto repeat;
 		}
-		VM_BUG_ON_PAGE(page_to_pgoff(page) != offset, page);
+		VM_BUG_ON_PAGE(!thp_contains(page, index), page);
 	}
 	return page;
 }
-EXPORT_SYMBOL(find_lock_entry);
 
 /**
  * pagecache_get_page - Find and get a reference to a page.
@@ -1643,6 +1737,8 @@ EXPORT_SYMBOL(find_lock_entry);
  *
  * * %FGP_ACCESSED - The page will be marked accessed.
  * * %FGP_LOCK - The page is returned locked.
+ * * %FGP_HEAD - If the page is present and a THP, return the head page
+ *   rather than the exact page specified by the index.
  * * %FGP_CREAT - If no page is present then a new page is allocated using
  *   @gfp_mask and added to the page cache and the VM's LRU list.
  *   The page is returned locked and with an increased refcount.
@@ -1683,12 +1779,12 @@ repeat:
 		}
 
 		/* Has the page been truncated? */
-		if (unlikely(compound_head(page)->mapping != mapping)) {
+		if (unlikely(page->mapping != mapping)) {
 			unlock_page(page);
 			put_page(page);
 			goto repeat;
 		}
-		VM_BUG_ON_PAGE(page->index != index, page);
+		VM_BUG_ON_PAGE(!thp_contains(page, index), page);
 	}
 
 	if (fgp_flags & FGP_ACCESSED)
@@ -1698,11 +1794,13 @@ repeat:
 		if (page_is_idle(page))
 			clear_page_idle(page);
 	}
+	if (!(fgp_flags & FGP_HEAD))
+		page = find_subpage(page, index);
 
 no_page:
 	if (!page && (fgp_flags & FGP_CREAT)) {
 		int err;
-		if ((fgp_flags & FGP_WRITE) && mapping_cap_account_dirty(mapping))
+		if ((fgp_flags & FGP_WRITE) && mapping_can_writeback(mapping))
 			gfp_mask |= __GFP_WRITE;
 		if (fgp_flags & FGP_NOFS)
 			gfp_mask &= ~__GFP_FS;
@@ -2267,7 +2365,11 @@ readpage:
 		}
 
 		if (!PageUptodate(page)) {
-			error = lock_page_killable(page);
+			if (iocb->ki_flags & IOCB_WAITQ)
+				error = lock_page_async(page, iocb->ki_waitq);
+			else
+				error = lock_page_killable(page);
+
 			if (unlikely(error))
 				goto readpage_error;
 			if (!PageUptodate(page)) {
@@ -2691,42 +2793,42 @@ void filemap_map_pages(struct vm_fault *vmf,
 	pgoff_t last_pgoff = start_pgoff;
 	unsigned long max_idx;
 	XA_STATE(xas, &mapping->i_pages, start_pgoff);
-	struct page *page;
+	struct page *head, *page;
 	unsigned int mmap_miss = READ_ONCE(file->f_ra.mmap_miss);
 
 	rcu_read_lock();
-	xas_for_each(&xas, page, end_pgoff) {
-		if (xas_retry(&xas, page))
+	xas_for_each(&xas, head, end_pgoff) {
+		if (xas_retry(&xas, head))
 			continue;
-		if (xa_is_value(page))
+		if (xa_is_value(head))
 			goto next;
 
 		/*
 		 * Check for a locked page first, as a speculative
 		 * reference may adversely influence page migration.
 		 */
-		if (PageLocked(page))
+		if (PageLocked(head))
 			goto next;
-		if (!page_cache_get_speculative(page))
+		if (!page_cache_get_speculative(head))
 			goto next;
 
 		/* Has the page moved or been split? */
-		if (unlikely(page != xas_reload(&xas)))
+		if (unlikely(head != xas_reload(&xas)))
 			goto skip;
-		page = find_subpage(page, xas.xa_index);
+		page = find_subpage(head, xas.xa_index);
 
-		if (!PageUptodate(page) ||
+		if (!PageUptodate(head) ||
 				PageReadahead(page) ||
 				PageHWPoison(page))
 			goto skip;
-		if (!trylock_page(page))
+		if (!trylock_page(head))
 			goto skip;
 
-		if (page->mapping != mapping || !PageUptodate(page))
+		if (head->mapping != mapping || !PageUptodate(head))
 			goto unlock;
 
 		max_idx = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE);
-		if (page->index >= max_idx)
+		if (xas.xa_index >= max_idx)
 			goto unlock;
 
 		if (mmap_miss > 0)
@@ -2738,12 +2840,12 @@ void filemap_map_pages(struct vm_fault *vmf,
 		last_pgoff = xas.xa_index;
 		if (alloc_set_pte(vmf, page))
 			goto unlock;
-		unlock_page(page);
+		unlock_page(head);
 		goto next;
 unlock:
-		unlock_page(page);
+		unlock_page(head);
 skip:
-		put_page(page);
+		put_page(head);
 next:
 		/* Huge page is mapped? No need to proceed. */
 		if (pmd_trans_huge(*vmf->pmd))