Messages in this thread | | | From | Geert Uytterhoeven <> | Date | Thu, 23 Mar 2017 19:49:53 +0100 | Subject | Re: [PATCH 00/13] Add HD44780 Character LCD support |
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Hi Willy,
On Thu, Mar 23, 2017 at 6:37 PM, Willy TARREAU <wtarreau@haproxy.com> wrote: > On Thu, Mar 23, 2017 at 06:15:01PM +0100, Willy TARREAU wrote: >> So I finally had the time to give it a try by applying your patchset >> on top of our 4.9 prod kernel. For now I'm getting a panic at boot : >> >> BUG: unable to handle kernel NULL pointer dereference at (null) >> IP: [<ffffffff813e203d>] __mutex_lock_slowpath+0x6d/0x100 > (...) > > It was indeed related to the backlight mutex. It's initialized > after charlcd_init_display() succeeds, but the backlight is > touched within this function. I just moved it upwards and that > solved the issue. Feel free to re-integrate this (or an equivalent) > into your patch. > > With only this fix, everything works fine here without even > having to touch the configuration, good job!
Thanks for testing!
> > Thanks! > Willy > -- > > diff --git a/drivers/auxdisplay/charlcd.c b/drivers/auxdisplay/charlcd.c > index 6aea900..e7f1bfe 100644 > --- a/drivers/auxdisplay/charlcd.c > +++ b/drivers/auxdisplay/charlcd.c > @@ -703,6 +703,8 @@ static int charlcd_init(struct charlcd *lcd) > struct charlcd_priv *priv = to_priv(lcd); > int ret; > > + mutex_init(&priv->bl_tempo_lock); > + > /* > * before this line, we must NOT send anything to the display. > * Since charlcd_init_display() needs to write data, we have to > @@ -713,7 +715,6 @@ static int charlcd_init(struct charlcd *lcd) > return ret; > > if (lcd->ops->backlight) { > - mutex_init(&priv->bl_tempo_lock); > INIT_DELAYED_WORK(&priv->bl_work, charlcd_bl_off); > }
I take it you're using v1 of the patchset?
v2 had this change:
- Move backlight mutex initialization before call to charlcd_init_display(), to prevent locking an uninitialized mutex (reported by 0day).
https://lkml.org/lkml/2017/3/10/1151
Gr{oetje,eeting}s,
Geert
-- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
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