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 <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Bartlomiej Zolnierkiewicz <[email protected]>
Cc: "Michał Mirosław" <[email protected]>
Cc: Peter Rosin <[email protected]>
Cc: Hans de Goede <[email protected]>
Cc: Mikulas Patocka <[email protected]>
Cc: Rob Clark <[email protected]>
---
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 = ␣
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
Hi Daniel.
On Fri, May 24, 2019 at 10:53:46AM +0200, Daniel Vetter wrote:
> There's a callchain of:
>
> fbcon_fb_blaned -> do_(un)blank_screen -> consw->con_blank
^^^^^^
Spelling error - as this is a callchain it would be good to have it
fixed.
Patch itself looks fine.
Sam
> -> 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 <[email protected]>
> Cc: Daniel Vetter <[email protected]>
> Cc: Bartlomiej Zolnierkiewicz <[email protected]>
> Cc: "Michał Mirosław" <[email protected]>
> Cc: Peter Rosin <[email protected]>
> Cc: Hans de Goede <[email protected]>
> Cc: Mikulas Patocka <[email protected]>
> Cc: Rob Clark <[email protected]>
> ---
> 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 = ␣
>
> 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
>
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