From bd0cda481fba8969d58411a31510692176c1dbaa Mon Sep 17 00:00:00 2001
From: Thomas Zimmermann <tzimmermann@suse.de>
Date: Fri, 11 Feb 2022 10:46:39 +0100
Subject: fbdev/defio: Early-out if page is already enlisted
Git-commit: 105a940416fc622406653b6fe54732897642dfbc
Patch-mainline: v5.18-rc1
References: jsc#PED-1166 jsc#PED-1168 jsc#PED-1170 jsc#PED-1218 jsc#PED-1220 jsc#PED-1222 jsc#PED-1223 jsc#PED-1225
Return early if a page is already in the list of dirty pages for
deferred I/O. This can be detected if the page's list head is not
empty. Keep the list head initialized while the page is not enlisted
to make this work reliably.
v2:
* update comment and fix spelling (Sam)
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220211094640.21632-2-tzimmermann@suse.de
Acked-by: Patrik Jakobsson <pjakobsson@suse.de>
---
drivers/video/fbdev/core/fb_defio.c | 26 +++++++++++++++++---------
1 file changed, 17 insertions(+), 9 deletions(-)
diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c
index a591d291b231..169a81c8172b 100644
--- a/drivers/video/fbdev/core/fb_defio.c
+++ b/drivers/video/fbdev/core/fb_defio.c
@@ -59,6 +59,7 @@ static vm_fault_t fb_deferred_io_fault(struct vm_fault *vmf)
printk(KERN_ERR "no mapping available\n");
BUG_ON(!page->mapping);
+ INIT_LIST_HEAD(&page->lru);
page->index = vmf->pgoff;
vmf->page = page;
@@ -122,17 +123,24 @@ static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf)
*/
lock_page(page);
+ /*
+ * This check is to catch the case where a new process could start
+ * writing to the same page through a new PTE. This new access
+ * can cause a call to .page_mkwrite even if the original process'
+ * PTE is marked writable.
+ *
+ * TODO: The lru field is owned by the page cache; hence the name.
+ * We dequeue in fb_deferred_io_work() after flushing the
+ * page's content into video memory. Instead of lru, fbdefio
+ * should have it's own field.
+ */
+ if (!list_empty(&page->lru))
+ goto page_already_added;
+
/* we loop through the pagelist before adding in order
to keep the pagelist sorted */
list_for_each_entry(cur, &fbdefio->pagelist, lru) {
- /* this check is to catch the case where a new
- process could start writing to the same page
- through a new pte. this new access can cause the
- mkwrite even when the original ps's pte is marked
- writable */
- if (unlikely(cur == page))
- goto page_already_added;
- else if (cur->index > page->index)
+ if (cur->index > page->index)
break;
}
@@ -194,7 +202,7 @@ static void fb_deferred_io_work(struct work_struct *work)
/* clear the list */
list_for_each_safe(node, next, &fbdefio->pagelist) {
- list_del(node);
+ list_del_init(node);
}
mutex_unlock(&fbdefio->lock);
}
--
2.38.1