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fbdev: Fix incorrect page mapping clearance at fb_deferred_io_release() 

commit fe9ae05cfb upstream.

The recent fix for the deferred I/O by the commit
  3efc61d952 ("fbdev: Fix invalid page access after closing deferred I/O devices")
caused a regression when the same fb device is opened/closed while
it's being used.  It resulted in a frozen screen even if something
is redrawn there after the close.  The breakage is because the patch
was made under a wrong assumption of a single open; in the current
code, fb_deferred_io_release() cleans up the page mapping of the
pageref list and it calls cancel_delayed_work_sync() unconditionally,
where both are no correct behavior for multiple opens.

This patch adds a refcount for the opens of the device, and applies
the cleanup only when all files get closed.

As both fb_deferred_io_open() and _close() are called always in the
fb_info lock (mutex), it's safe to use the normal int for the
refcounting.

Also, a useless BUG_ON() is dropped.

Fixes: 3efc61d952 ("fbdev: Fix invalid page access after closing deferred I/O devices")
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Reviewed-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230308105012.1845-1-tiwai@suse.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Takashi Iwai 2023-03-08 11:50:12 +01:00 committed by Greg Kroah-Hartman
parent 697893e0da
commit 1ea3e18e53
2 changed files with 14 additions and 4 deletions
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17
drivers/video/fbdev/core/fb_defio.c
View File

@ -309,17 +309,18 @@ void fb_deferred_io_open(struct fb_info *info,
struct inode *inode,
struct file *file)
{
struct fb_deferred_io *fbdefio = info->fbdefio;
file->f_mapping->a_ops = &fb_deferred_io_aops;
fbdefio->open_count++;
}
EXPORT_SYMBOL_GPL(fb_deferred_io_open);
void fb_deferred_io_release(struct fb_info *info)
static void fb_deferred_io_lastclose(struct fb_info *info)
{
struct fb_deferred_io *fbdefio = info->fbdefio;
struct page *page;
int i;
BUG_ON(!fbdefio);
cancel_delayed_work_sync(&info->deferred_work);
/* clear out the mapping that we setup */
@ -328,13 +329,21 @@ void fb_deferred_io_release(struct fb_info *info)
page->mapping = NULL;
}
}
void fb_deferred_io_release(struct fb_info *info)
{
struct fb_deferred_io *fbdefio = info->fbdefio;
if (!--fbdefio->open_count)
fb_deferred_io_lastclose(info);
}
EXPORT_SYMBOL_GPL(fb_deferred_io_release);
void fb_deferred_io_cleanup(struct fb_info *info)
{
struct fb_deferred_io *fbdefio = info->fbdefio;
fb_deferred_io_release(info);
fb_deferred_io_lastclose(info);
kvfree(info->pagerefs);
mutex_destroy(&fbdefio->lock);

1
include/linux/fb.h
View File

@ -212,6 +212,7 @@ struct fb_deferred_io {
/* delay between mkwrite and deferred handler */
unsigned long delay;
bool sort_pagereflist; /* sort pagelist by offset */
int open_count; /* number of opened files; protected by fb_info lock */
struct mutex lock; /* mutex that protects the pageref list */
struct list_head pagereflist; /* list of pagerefs for touched pages */
/* callback */