From 49bbd815fd8ba26d0354900b783b767c7f47c816 Mon Sep 17 00:00:00 2001 From: Albert Herranz Date: Mon, 24 May 2010 14:34:08 -0700 Subject: [PATCH] fb_defio: fix for non-dirty ptes Fix a problem observed while using fb_defio with a short delay on a PowerPC platform. It is possible that page_mkclean() is invoked in the deferred io work function _before_ a PTE has been marked dirty. In this case, the page is removed from the defio pagelist but page_mkclean() does not write-protect the page again. The end result is that defio ignores all subsequent writes to the page and the corresponding portions of the framebuffer never get updated. The fix consists in keeping track of the pages with non-dirty PTEs, re-checking them again on the next deferred io work iteration. Note that those pages are not passed to the defio callback as they are not written by userspace yet. Signed-off-by: Albert Herranz Acked-by: Jaya Kumar Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/video/fb_defio.c | 40 ++++++++++++++++++++++++++++++++-------- 1 file changed, 32 insertions(+), 8 deletions(-) diff --git a/drivers/video/fb_defio.c b/drivers/video/fb_defio.c index 6113c47..1105a59 100644 --- a/drivers/video/fb_defio.c +++ b/drivers/video/fb_defio.c @@ -155,25 +155,41 @@ static void fb_deferred_io_work(struct work_struct *work) { struct fb_info *info = container_of(work, struct fb_info, deferred_work.work); - struct list_head *node, *next; - struct page *cur; struct fb_deferred_io *fbdefio = info->fbdefio; + struct page *page, *tmp_page; + struct list_head *node, *tmp_node; + struct list_head non_dirty; + + INIT_LIST_HEAD(&non_dirty); /* here we mkclean the pages, then do all deferred IO */ mutex_lock(&fbdefio->lock); - list_for_each_entry(cur, &fbdefio->pagelist, lru) { - lock_page(cur); - page_mkclean(cur); - unlock_page(cur); + list_for_each_entry_safe(page, tmp_page, &fbdefio->pagelist, lru) { + lock_page(page); + /* + * The workqueue callback can be triggered after a + * ->page_mkwrite() call but before the PTE has been marked + * dirty. In this case page_mkclean() won't "rearm" the page. + * + * To avoid this, remove those "non-dirty" pages from the + * pagelist before calling the driver's callback, then add + * them back to get processed on the next work iteration. + * At that time, their PTEs will hopefully be dirty for real. + */ + if (!page_mkclean(page)) + list_move_tail(&page->lru, &non_dirty); + unlock_page(page); } /* driver's callback with pagelist */ fbdefio->deferred_io(info, &fbdefio->pagelist); - /* clear the list */ - list_for_each_safe(node, next, &fbdefio->pagelist) { + /* clear the list... */ + list_for_each_safe(node, tmp_node, &fbdefio->pagelist) { list_del(node); } + /* ... and add back the "non-dirty" pages to the list */ + list_splice_tail(&non_dirty, &fbdefio->pagelist); mutex_unlock(&fbdefio->lock); } @@ -202,6 +218,7 @@ EXPORT_SYMBOL_GPL(fb_deferred_io_open); void fb_deferred_io_cleanup(struct fb_info *info) { struct fb_deferred_io *fbdefio = info->fbdefio; + struct list_head *node, *tmp_node; struct page *page; int i; @@ -209,6 +226,13 @@ void fb_deferred_io_cleanup(struct fb_info *info) cancel_delayed_work(&info->deferred_work); flush_scheduled_work(); + /* the list may have still some non-dirty pages at this point */ + mutex_lock(&fbdefio->lock); + list_for_each_safe(node, tmp_node, &fbdefio->pagelist) { + list_del(node); + } + mutex_unlock(&fbdefio->lock); + /* clear out the mapping that we setup */ for (i = 0 ; i < info->fix.smem_len; i += PAGE_SIZE) { page = fb_deferred_io_page(info, i); -- 1.8.2.3