[PATCH 25/33] fbmem: pull fbcon_fb_blanked out of fb_blank

Daniel Vetter
2019-05-24T08:53:46Z

There's a callchain of:

fbcon_fb_blaned -> do_(un)blank_screen -> consw->con_blank
-> fbcon_blank -> fb_blank

Things don't go horribly wrong because the BKL console_lock safes the
day, but that's about it. And the seeming recursion is broken in 2
ways:
- Starting from the fbdev ioctl we set FBINFO_MISC_USEREVENT, which
tells the fbcon_blank code to not call fb_blank. This was required
to not deadlock when recursing on the fb_notifier_chain mutex.
- Starting from the con_blank hook we're getting saved by the
console_blanked checks in do_blank/unblank_screen. Or at least
that's my theory.

Anyway, recursion isn't awesome, so let's stop it. Breaking the
recursion avoids the need to be in the FBINFO_MISC_USEREVENT critical
section, so lets move it out of that too.

The astute reader will notice that fb_blank seems to require
lock_fb_info(), which the fbcon code seems to ignore. I have no idea
how to fix that problem, so let's keep ignoring it.

v2: I forgot the sysfs blanking code.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: "Michał Mirosław" <mirq-linux@rere.qmqm.pl>
Cc: Peter Rosin <peda@axentia.se>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Rob Clark <robdclark@gmail.com>
---
drivers/video/fbdev/core/fbmem.c | 4 +++-
drivers/video/fbdev/core/fbsysfs.c | 8 ++++++--
2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 9366fbe99a58..d6713dce9e31 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1068,7 +1068,6 @@ fb_blank(struct fb_info *info, int blank)
event.data = &blank;

early_ret = fb_notifier_call_chain(FB_EARLY_EVENT_BLANK, &event);
- fbcon_fb_blanked(info, blank);

if (info->fbops->fb_blank)
ret = info->fbops->fb_blank(blank, info);
@@ -1198,6 +1197,9 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
info->flags |= FBINFO_MISC_USEREVENT;
ret = fb_blank(info, arg);
info->flags &= ~FBINFO_MISC_USEREVENT;
+
+ /* might again call into fb_blank */
+ fbcon_fb_blanked(info, arg);
unlock_fb_info(info);
console_unlock();
break;
diff --git a/drivers/video/fbdev/core/fbsysfs.c b/drivers/video/fbdev/core/fbsysfs.c
index 5f329278e55f..252d4f52d2a5 100644
--- a/drivers/video/fbdev/core/fbsysfs.c
+++ b/drivers/video/fbdev/core/fbsysfs.c
@@ -18,6 +18,7 @@
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/fb.h>
+#include <linux/fbcon.h>
#include <linux/console.h>
#include <linux/module.h>

@@ -305,12 +306,15 @@ static ssize_t store_blank(struct device *device,
{
struct fb_info *fb_info = dev_get_drvdata(device);
char *last = NULL;
- int err;
+ int err, arg;

+ arg = simple_strtoul(buf, &last, 0);
console_lock();
fb_info->flags |= FBINFO_MISC_USEREVENT;
- err = fb_blank(fb_info, simple_strtoul(buf, &last, 0));
+ err = fb_blank(fb_info, arg);
fb_info->flags &= ~FBINFO_MISC_USEREVENT;
+ /* might again call into fb_blank */
+ fbcon_fb_blanked(fb_info, arg);
console_unlock();
if (err < 0)
return err;
--
2.20.1