| Message ID | 20160622100422.5c34f975@bbrezillon (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | Geert Uytterhoeven |
| Headers | show |
On Wed, Jun 22, 2016 at 10:04:22AM +0200, Boris Brezillon wrote: > On Tue, 21 Jun 2016 11:37:31 -0700 > Brian Norris <briannorris@chromium.org> wrote: > > > Hi Geert, > > > > On Tue, Jun 21, 2016 at 04:42:04PM +0200, Geert Uytterhoeven wrote: > > > On Fri, May 27, 2016 at 6:45 PM, Brian Norris <briannorris@chromium.org> wrote: > > > > It seems like in the process of refactoring pwm_config() to utilize the > > > > newly-introduced pwm_apply_state() API, some args/bounds checking was > > > > dropped. > > > > > > > > In particular, I noted that we are now allowing invalid period > > > > selections. e.g.: > > > > > > > > # echo 1 > /sys/class/pwm/pwmchip0/export > > > > # cat /sys/class/pwm/pwmchip0/pwm1/period > > > > 100 > > > > # echo 101 > /sys/class/pwm/pwmchip0/pwm1/duty_cycle > > > > [... driver may or may not reject the value, or trigger some logic bug ...] > > > > > > > > It's better to see: > > > > > > > > # echo 1 > /sys/class/pwm/pwmchip0/export > > > > # cat /sys/class/pwm/pwmchip0/pwm1/period > > > > 100 > > > > # echo 101 > /sys/class/pwm/pwmchip0/pwm1/duty_cycle > > > > -bash: echo: write error: Invalid argument > > > > > > > > This patch reintroduces some bounds checks in both pwm_config() (for its > > > > signed parameters; we don't want to convert negative values into large > > > > unsigned values) and in pwm_apply_state() (which fix the above described > > > > behavior, as well as other potential API misuses). > > > > > > > > Fixes: 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic updates") > > > > Signed-off-by: Brian Norris <briannorris@chromium.org> > > > > --- > > > > v2: > > > > * changed subject, as this covers more scope now > > > > * add Fixes tag, as this is a v4.7-rc regression > > > > * add more bounds/args checks in pwm_apply_state() and pwm_config() > > > > > > > > drivers/pwm/core.c | 3 ++- > > > > include/linux/pwm.h | 3 +++ > > > > 2 files changed, 5 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c > > > > index dba3843c53b8..ed337a8c34ab 100644 > > > > --- a/drivers/pwm/core.c > > > > +++ b/drivers/pwm/core.c > > > > @@ -457,7 +457,8 @@ int pwm_apply_state(struct pwm_device *pwm, struct pwm_state *state) > > > > { > > > > int err; > > > > > > > > - if (!pwm) > > > > + if (!pwm || !state || !state->period || > > > > + state->duty_cycle > state->period) > > > > return -EINVAL; > > > > > > This check breaks the LCD backlight on r8a7740/armadillo. > > > Apparently both period and duty_cycle are zero during the first invocation. > > > Later, these are initialized from DT, cfr. > > > > > > pwms = <&tpu 2 33333 PWM_POLARITY_INVERTED>; > > > > > > in arch/arm/boot/dts/r8a7740-armadillo800eva.dts. > > > > Hmm, this isn't super obvious how to best fix. On one hand, the > > pwm_config() API used to reject period<=0, but on the other hand, I > > think its replacement (pwm_apply_state()) is getting used in more places > > than it used to be, and not all of them are really handling the "atomic > > update" concept yet. Seems like a product of Boris's multi-phase attempt > > to convert the PWM APIs to support atomic updates -- and many users > > haven't really converted yet. > > > > > With added debug printing, the difference between failure and success is: > > > > > > renesas-tpu-pwm e6600000.pwm: TPU PWM -1 registered > > > tpu_pwm_request:223 > > > pwm_apply_state:460: pwm backlight/2: period 0, duty_cycle 0 > > > +Ignoring failure > > > +pwm_apply_state:479: polarity 0 -> 1 > > > +tpu_pwm_set_polarity:343 > > > +pwm_apply_state:502: period 0 -> 0 > > > +pwm_apply_state:503: duty_cycle 0 -> 0 > > > +pwm_apply_state:516: enabled 0 -> 0 > > > pwm_config:238: pwm backlight/2: duty_ns 33333, period_ns 33333 > > > pwm_apply_state:460: pwm backlight/2: period 33333, duty_cycle 33333 > > > -pwm_apply_state:479: polarity 0 -> 0 > > > +pwm_apply_state:479: polarity 1 -> 1 > > > pwm_apply_state:502: period 0 -> 33333 > > > pwm_apply_state:503: duty_cycle 0 -> 33333 > > > tpu_pwm_config:267 > > > pwm_apply_state:516: enabled 0 -> 0 > > > pwm_apply_state:460: pwm backlight/2: period 33333, duty_cycle 33333 > > > -pwm_apply_state:479: polarity 0 -> 0 > > > +pwm_apply_state:479: polarity 1 -> 1 > > > pwm_apply_state:502: period 33333 -> 33333 > > > pwm_apply_state:503: duty_cycle 33333 -> 33333 > > > pwm_apply_state:516: enabled 0 -> 1 > > > tpu_pwm_enable:354 > > > > I'm not sure I 100% understand this debug log, but I think maybe the > > problem is in pwm_apply_args(), which calls pwm_disable() and > > pwm_set_polarity() sequentially, without ever configuring a period? What > > if pwm_apply_args() were to configure the period for us? > > > > Boris, any thoughts? > > > > I had second thoughts and I think you're right: pwm_apply_args() > should set the pargs.period period for us. > > Here is a patch addressing that. > > Geert, can you test it? > > --->8--- > From 0610f7e24976e176054bce20445ff42d8aea9513 Mon Sep 17 00:00:00 2001 > From: Boris Brezillon <boris.brezillon@free-electrons.com> > Date: Wed, 22 Jun 2016 09:25:14 +0200 > Subject: [PATCH] pwm: Fix pwm_apply_args() > > Commit 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic > updates"), implemented pwm_disable() as a wrapper around > pwm_apply_state(), and then, commit ef2bf4997f7d ("pwm: Improve args > checking in pwm_apply_state()") added missing checks on the ->period > value in pwm_apply_state() to ensure we were not passing inappropriate > values to the ->config() or ->apply() methods. > > The conjunction of these 2 commits led to a case where pwm_disable() > was no longer succeeding, thus preventing the polarity setting done > in pwm_apply_args(). > > Set a valid period in pwm_apply_args() to ensure polarity setting > won't be rejected. > > Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com> > Reported-by: Geert Uytterhoeven <geert@linux-m68k.org> > Suggested-by: Brian Norris <briannorris@chromium.org> > Fixes: 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic updates") > --- > include/linux/pwm.h | 16 ++++++++++------ > 1 file changed, 10 insertions(+), 6 deletions(-) > > diff --git a/include/linux/pwm.h b/include/linux/pwm.h > index 908b67c847cd..c038ae36b10e 100644 > --- a/include/linux/pwm.h > +++ b/include/linux/pwm.h > @@ -464,6 +464,8 @@ static inline bool pwm_can_sleep(struct pwm_device *pwm) > > static inline void pwm_apply_args(struct pwm_device *pwm) > { > + struct pwm_state state = { }; > + > /* > * PWM users calling pwm_apply_args() expect to have a fresh config > * where the polarity and period are set according to pwm_args info. > @@ -476,18 +478,20 @@ static inline void pwm_apply_args(struct pwm_device *pwm) > * at startup (even if they are actually enabled), thus authorizing > * polarity setting. > * > - * Instead of setting ->enabled to false, we call pwm_disable() > - * before pwm_set_polarity() to ensure that everything is configured > - * as expected, and the PWM is really disabled when the user request > - * it. > + * To fulfill this requirement, we apply a new state which disables > + * the PWM device and set the reference period and polarity config. > * > * Note that PWM users requiring a smooth handover between the > * bootloader and the kernel (like critical regulators controlled by > * PWM devices) will have to switch to the atomic API and avoid calling > * pwm_apply_args(). > */ > - pwm_disable(pwm); > - pwm_set_polarity(pwm, pwm->args.polarity); > + > + state.enabled = false; > + state.polarity = pwm->args.polarity; > + state.period = pwm->args.period; > + > + pwm_apply_state(pwm, &state); > } > > struct pwm_lookup { This looks reasonable to me. I'll wait for a Tested-by from Geert before applying, though. Thierry
Hi Boris, On Wed, Jun 22, 2016 at 10:04 AM, Boris Brezillon <boris.brezillon@free-electrons.com> wrote: > On Tue, 21 Jun 2016 11:37:31 -0700 > Brian Norris <briannorris@chromium.org> wrote: >> On Tue, Jun 21, 2016 at 04:42:04PM +0200, Geert Uytterhoeven wrote: >> > On Fri, May 27, 2016 at 6:45 PM, Brian Norris <briannorris@chromium.org> wrote: >> > > It seems like in the process of refactoring pwm_config() to utilize the >> > > newly-introduced pwm_apply_state() API, some args/bounds checking was >> > > dropped. >> > > >> > > In particular, I noted that we are now allowing invalid period >> > > selections. e.g.: >> > > >> > > # echo 1 > /sys/class/pwm/pwmchip0/export >> > > # cat /sys/class/pwm/pwmchip0/pwm1/period >> > > 100 >> > > # echo 101 > /sys/class/pwm/pwmchip0/pwm1/duty_cycle >> > > [... driver may or may not reject the value, or trigger some logic bug ...] >> > > >> > > It's better to see: >> > > >> > > # echo 1 > /sys/class/pwm/pwmchip0/export >> > > # cat /sys/class/pwm/pwmchip0/pwm1/period >> > > 100 >> > > # echo 101 > /sys/class/pwm/pwmchip0/pwm1/duty_cycle >> > > -bash: echo: write error: Invalid argument >> > > >> > > This patch reintroduces some bounds checks in both pwm_config() (for its >> > > signed parameters; we don't want to convert negative values into large >> > > unsigned values) and in pwm_apply_state() (which fix the above described >> > > behavior, as well as other potential API misuses). >> > > >> > > Fixes: 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic updates") >> > > Signed-off-by: Brian Norris <briannorris@chromium.org> >> > > --- >> > > v2: >> > > * changed subject, as this covers more scope now >> > > * add Fixes tag, as this is a v4.7-rc regression >> > > * add more bounds/args checks in pwm_apply_state() and pwm_config() >> > > >> > > drivers/pwm/core.c | 3 ++- >> > > include/linux/pwm.h | 3 +++ >> > > 2 files changed, 5 insertions(+), 1 deletion(-) >> > > >> > > diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c >> > > index dba3843c53b8..ed337a8c34ab 100644 >> > > --- a/drivers/pwm/core.c >> > > +++ b/drivers/pwm/core.c >> > > @@ -457,7 +457,8 @@ int pwm_apply_state(struct pwm_device *pwm, struct pwm_state *state) >> > > { >> > > int err; >> > > >> > > - if (!pwm) >> > > + if (!pwm || !state || !state->period || >> > > + state->duty_cycle > state->period) >> > > return -EINVAL; >> > >> > This check breaks the LCD backlight on r8a7740/armadillo. >> I'm not sure I 100% understand this debug log, but I think maybe the >> problem is in pwm_apply_args(), which calls pwm_disable() and >> pwm_set_polarity() sequentially, without ever configuring a period? What >> if pwm_apply_args() were to configure the period for us? >> >> Boris, any thoughts? >> > > I had second thoughts and I think you're right: pwm_apply_args() > should set the pargs.period period for us. > > Here is a patch addressing that. > > Geert, can you test it? > > --->8--- > From 0610f7e24976e176054bce20445ff42d8aea9513 Mon Sep 17 00:00:00 2001 > From: Boris Brezillon <boris.brezillon@free-electrons.com> > Date: Wed, 22 Jun 2016 09:25:14 +0200 > Subject: [PATCH] pwm: Fix pwm_apply_args() > > Commit 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic > updates"), implemented pwm_disable() as a wrapper around > pwm_apply_state(), and then, commit ef2bf4997f7d ("pwm: Improve args > checking in pwm_apply_state()") added missing checks on the ->period > value in pwm_apply_state() to ensure we were not passing inappropriate > values to the ->config() or ->apply() methods. > > The conjunction of these 2 commits led to a case where pwm_disable() > was no longer succeeding, thus preventing the polarity setting done > in pwm_apply_args(). > > Set a valid period in pwm_apply_args() to ensure polarity setting > won't be rejected. > > Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com> > Reported-by: Geert Uytterhoeven <geert@linux-m68k.org> > Suggested-by: Brian Norris <briannorris@chromium.org> > Fixes: 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic updates") Tested-by: Geert Uytterhoeven <geert+renesas@glider.be> 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
On Wed, Jun 22, 2016 at 10:04:22AM +0200, Boris Brezillon wrote: > From 0610f7e24976e176054bce20445ff42d8aea9513 Mon Sep 17 00:00:00 2001 > From: Boris Brezillon <boris.brezillon@free-electrons.com> > Date: Wed, 22 Jun 2016 09:25:14 +0200 > Subject: [PATCH] pwm: Fix pwm_apply_args() > > Commit 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic > updates"), implemented pwm_disable() as a wrapper around > pwm_apply_state(), and then, commit ef2bf4997f7d ("pwm: Improve args > checking in pwm_apply_state()") added missing checks on the ->period > value in pwm_apply_state() to ensure we were not passing inappropriate > values to the ->config() or ->apply() methods. > > The conjunction of these 2 commits led to a case where pwm_disable() > was no longer succeeding, thus preventing the polarity setting done > in pwm_apply_args(). > > Set a valid period in pwm_apply_args() to ensure polarity setting > won't be rejected. > > Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com> > Reported-by: Geert Uytterhoeven <geert@linux-m68k.org> > Suggested-by: Brian Norris <briannorris@chromium.org> > Fixes: 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic updates") > --- > include/linux/pwm.h | 16 ++++++++++------ > 1 file changed, 10 insertions(+), 6 deletions(-) > > diff --git a/include/linux/pwm.h b/include/linux/pwm.h > index 908b67c847cd..c038ae36b10e 100644 > --- a/include/linux/pwm.h > +++ b/include/linux/pwm.h > @@ -464,6 +464,8 @@ static inline bool pwm_can_sleep(struct pwm_device *pwm) > > static inline void pwm_apply_args(struct pwm_device *pwm) > { > + struct pwm_state state = { }; > + > /* > * PWM users calling pwm_apply_args() expect to have a fresh config > * where the polarity and period are set according to pwm_args info. > @@ -476,18 +478,20 @@ static inline void pwm_apply_args(struct pwm_device *pwm) > * at startup (even if they are actually enabled), thus authorizing > * polarity setting. > * > - * Instead of setting ->enabled to false, we call pwm_disable() > - * before pwm_set_polarity() to ensure that everything is configured > - * as expected, and the PWM is really disabled when the user request > - * it. I was confused by this original text when reading it the first time. I like the replacement text and implementation, as it seems to make more sense. > + * To fulfill this requirement, we apply a new state which disables > + * the PWM device and set the reference period and polarity config. > * > * Note that PWM users requiring a smooth handover between the > * bootloader and the kernel (like critical regulators controlled by > * PWM devices) will have to switch to the atomic API and avoid calling > * pwm_apply_args(). > */ > - pwm_disable(pwm); > - pwm_set_polarity(pwm, pwm->args.polarity); Notably, you're dropping the 'if (!pwm) { }' safety checks that are part of pwm_disable() and pwm_set_polarity(). But I don't think there should be any users relying on that. > + > + state.enabled = false; > + state.polarity = pwm->args.polarity; > + state.period = pwm->args.period; > + > + pwm_apply_state(pwm, &state); > } > > struct pwm_lookup { Reviewed-by: Brian Norris <briannorris@chromium.org>
On Wed, 22 Jun 2016 12:16:59 -0700 Brian Norris <briannorris@chromium.org> wrote: > On Wed, Jun 22, 2016 at 10:04:22AM +0200, Boris Brezillon wrote: > > From 0610f7e24976e176054bce20445ff42d8aea9513 Mon Sep 17 00:00:00 2001 > > From: Boris Brezillon <boris.brezillon@free-electrons.com> > > Date: Wed, 22 Jun 2016 09:25:14 +0200 > > Subject: [PATCH] pwm: Fix pwm_apply_args() > > > > Commit 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic > > updates"), implemented pwm_disable() as a wrapper around > > pwm_apply_state(), and then, commit ef2bf4997f7d ("pwm: Improve args > > checking in pwm_apply_state()") added missing checks on the ->period > > value in pwm_apply_state() to ensure we were not passing inappropriate > > values to the ->config() or ->apply() methods. > > > > The conjunction of these 2 commits led to a case where pwm_disable() > > was no longer succeeding, thus preventing the polarity setting done > > in pwm_apply_args(). > > > > Set a valid period in pwm_apply_args() to ensure polarity setting > > won't be rejected. > > > > Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com> > > Reported-by: Geert Uytterhoeven <geert@linux-m68k.org> > > Suggested-by: Brian Norris <briannorris@chromium.org> > > Fixes: 5ec803edcb70 ("pwm: Add core infrastructure to allow atomic updates") > > --- > > include/linux/pwm.h | 16 ++++++++++------ > > 1 file changed, 10 insertions(+), 6 deletions(-) > > > > diff --git a/include/linux/pwm.h b/include/linux/pwm.h > > index 908b67c847cd..c038ae36b10e 100644 > > --- a/include/linux/pwm.h > > +++ b/include/linux/pwm.h > > @@ -464,6 +464,8 @@ static inline bool pwm_can_sleep(struct pwm_device *pwm) > > > > static inline void pwm_apply_args(struct pwm_device *pwm) > > { > > + struct pwm_state state = { }; > > + > > /* > > * PWM users calling pwm_apply_args() expect to have a fresh config > > * where the polarity and period are set according to pwm_args info. > > @@ -476,18 +478,20 @@ static inline void pwm_apply_args(struct pwm_device *pwm) > > * at startup (even if they are actually enabled), thus authorizing > > * polarity setting. > > * > > - * Instead of setting ->enabled to false, we call pwm_disable() > > - * before pwm_set_polarity() to ensure that everything is configured > > - * as expected, and the PWM is really disabled when the user request > > - * it. > > I was confused by this original text when reading it the first time. I > like the replacement text and implementation, as it seems to make more > sense. Well, it should have been done this way from the beginning, but pwm_apply_args() was introduced before the commit introducing the atomic APIs, and I forgot to update it when moving to the atomic approach :-/. > > > + * To fulfill this requirement, we apply a new state which disables > > + * the PWM device and set the reference period and polarity config. > > * > > * Note that PWM users requiring a smooth handover between the > > * bootloader and the kernel (like critical regulators controlled by > > * PWM devices) will have to switch to the atomic API and avoid calling > > * pwm_apply_args(). > > */ > > - pwm_disable(pwm); > > - pwm_set_polarity(pwm, pwm->args.polarity); > > Notably, you're dropping the 'if (!pwm) { }' safety checks that are part > of pwm_disable() and pwm_set_polarity(). But I don't think there should > be any users relying on that. Indeed. I can add it back here if you prefer, but honestly, PWM users that are not checking the value returned by pwm_get() should be considered buggy IMHO, and a NULL pointer exception is a good way to make people realize they are not properly using the API :). > > > + > > + state.enabled = false; > > + state.polarity = pwm->args.polarity; > > + state.period = pwm->args.period; > > + > > + pwm_apply_state(pwm, &state); > > } > > > > struct pwm_lookup { > > Reviewed-by: Brian Norris <briannorris@chromium.org>
On Wed, Jun 22, 2016 at 10:41:14PM +0200, Boris Brezillon wrote: > On Wed, 22 Jun 2016 12:16:59 -0700 > Brian Norris <briannorris@chromium.org> wrote: > > Notably, you're dropping the 'if (!pwm) { }' safety checks that are part > > of pwm_disable() and pwm_set_polarity(). But I don't think there should > > be any users relying on that. > > Indeed. I can add it back here if you prefer, Nah, that's ok. I just had to say it anyway :) > but honestly, PWM users > that are not checking the value returned by pwm_get() should be > considered buggy IMHO, and a NULL pointer exception is a good way to > make people realize they are not properly using the API :). Seems OK. Brian
On Wed, Jun 22, 2016 at 01:46:48PM -0700, Brian Norris wrote: > On Wed, Jun 22, 2016 at 10:41:14PM +0200, Boris Brezillon wrote: > > On Wed, 22 Jun 2016 12:16:59 -0700 > > Brian Norris <briannorris@chromium.org> wrote: > > > Notably, you're dropping the 'if (!pwm) { }' safety checks that are part > > > of pwm_disable() and pwm_set_polarity(). But I don't think there should > > > be any users relying on that. > > > > Indeed. I can add it back here if you prefer, > > Nah, that's ok. I just had to say it anyway :) > > > but honestly, PWM users > > that are not checking the value returned by pwm_get() should be > > considered buggy IMHO, and a NULL pointer exception is a good way to > > make people realize they are not properly using the API :). > > Seems OK. I've applied this to my fixes branch, and I'll let it cook in linux-next for a little while, then send it off to Linus for v4.7-rc6 next week if no further fallout is caused by this. Thierry
diff --git a/include/linux/pwm.h b/include/linux/pwm.h index 908b67c847cd..c038ae36b10e 100644 --- a/include/linux/pwm.h +++ b/include/linux/pwm.h @@ -464,6 +464,8 @@ static inline bool pwm_can_sleep(struct pwm_device *pwm) static inline void pwm_apply_args(struct pwm_device *pwm) { + struct pwm_state state = { }; + /* * PWM users calling pwm_apply_args() expect to have a fresh config * where the polarity and period are set according to pwm_args info. @@ -476,18 +478,20 @@ static inline void pwm_apply_args(struct pwm_device *pwm) * at startup (even if they are actually enabled), thus authorizing * polarity setting. * - * Instead of setting ->enabled to false, we call pwm_disable() - * before pwm_set_polarity() to ensure that everything is configured - * as expected, and the PWM is really disabled when the user request - * it. + * To fulfill this requirement, we apply a new state which disables + * the PWM device and set the reference period and polarity config. * * Note that PWM users requiring a smooth handover between the * bootloader and the kernel (like critical regulators controlled by * PWM devices) will have to switch to the atomic API and avoid calling * pwm_apply_args(). */ - pwm_disable(pwm); - pwm_set_polarity(pwm, pwm->args.polarity); + + state.enabled = false; + state.polarity = pwm->args.polarity; + state.period = pwm->args.period; + + pwm_apply_state(pwm, &state); } struct pwm_lookup {