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fbdev/defio: Early-out if page is already enlisted

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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
This commit is contained in:
Thomas Zimmermann 2022-02-11 10:46:39 +01:00
parent 21d26b3972
commit 105a940416
1 changed files with 17 additions and 9 deletions
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26
drivers/video/fbdev/core/fb_defio.c
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@ -59,6 +59,7 @@ static vm_fault_t fb_deferred_io_fault(struct vm_fault *vmf)
printk(KERN_ERR "no mapping available\n"); printk(KERN_ERR "no mapping available\n");
BUG_ON(!page->mapping); BUG_ON(!page->mapping);
INIT_LIST_HEAD(&page->lru);
page->index = vmf->pgoff; page->index = vmf->pgoff;
vmf->page = page; vmf->page = page;
@ -122,17 +123,24 @@ static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf)
*/ */
lock_page(page); 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 /* we loop through the pagelist before adding in order
to keep the pagelist sorted */ to keep the pagelist sorted */
list_for_each_entry(cur, &fbdefio->pagelist, lru) { list_for_each_entry(cur, &fbdefio->pagelist, lru) {
/* this check is to catch the case where a new if (cur->index > page->index)
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)
break; break;
} }
@ -194,7 +202,7 @@ static void fb_deferred_io_work(struct work_struct *work)
/* clear the list */ /* clear the list */
list_for_each_safe(node, next, &fbdefio->pagelist) { list_for_each_safe(node, next, &fbdefio->pagelist) {
list_del(node); list_del_init(node);
} }
mutex_unlock(&fbdefio->lock); mutex_unlock(&fbdefio->lock);
} }