On Wed, Mar 8, 2023 at 7:36 AM Takashi Iwai <tiwai@xxxxxxx> wrote: > > The recent fix for the deferred I/O by the commit > 3efc61d95259 ("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. > > Fixes: 3efc61d95259 ("fbdev: Fix invalid page access after closing deferred I/O devices") > Cc: <stable@xxxxxxxxxxxxxxx> > Signed-off-by: Takashi Iwai <tiwai@xxxxxxx> > --- > drivers/video/fbdev/core/fb_defio.c | 16 +++++++++++++--- > include/linux/fb.h | 1 + > 2 files changed, 14 insertions(+), 3 deletions(-) > > diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c > index aa5f059d0222..9dcec9e020b6 100644 > --- a/drivers/video/fbdev/core/fb_defio.c > +++ b/drivers/video/fbdev/core/fb_defio.c > @@ -305,17 +305,19 @@ 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->opens++; > } > EXPORT_SYMBOL_GPL(fb_deferred_io_open); > > -void fb_deferred_io_release(struct fb_info *info) > +static void fb_deferred_io_release_internal(struct fb_info *info) Maybe a better name would be fb_deferred_io_lastclose() to be more in line with DRM? > { > struct fb_deferred_io *fbdefio = info->fbdefio; > struct page *page; > int i; > > - BUG_ON(!fbdefio); Should the BUG_ON be put back into fb_deferred_io_release()? > cancel_delayed_work_sync(&info->deferred_work); > > /* clear out the mapping that we setup */ > @@ -324,13 +326,21 @@ 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->opens) > + fb_deferred_io_release_internal(info); I think this can race so we need locking. > +} > 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_release_internal(info); > > kvfree(info->pagerefs); > mutex_destroy(&fbdefio->lock); > diff --git a/include/linux/fb.h b/include/linux/fb.h > index d8d20514ea05..29674a29d1c4 100644 > --- a/include/linux/fb.h > +++ b/include/linux/fb.h > @@ -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 opens; /* number of opened files */ I would prefer the name num_opens (or open_count as in DRM) instead of opens since it can be interpreted as a verb. Also, don't we need it to be atomic_t? > struct mutex lock; /* mutex that protects the pageref list */ > struct list_head pagereflist; /* list of pagerefs for touched pages */ > /* callback */ > -- > 2.35.3 >