From: Marek Vasut <marex@denx.de> To: Johan Hovold <johan@kernel.org>, Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: linux-serial@vger.kernel.org, Alexandre Torgue <alexandre.torgue@foss.st.com>, Erwan Le Ray <erwan.leray@foss.st.com>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Jiri Slaby <jirislaby@kernel.org>, Maxime Coquelin <mcoquelin.stm32@gmail.com>, Thomas Gleixner <tglx@linutronix.de>, Valentin Caron <valentin.caron@foss.st.com>, linux-arm-kernel@lists.infradead.org, linux-stm32@st-md-mailman.stormreply.com Subject: Re: [PATCH v3] serial: stm32: Merge hard IRQ and threaded IRQ handling into single IRQ handler Date: Thu, 12 Jan 2023 17:38:48 +0100 [thread overview] Message-ID: <78e3f61f-4f87-9ac5-7c7c-172714da69d3@denx.de> (raw) In-Reply-To: <Y8AHaJIttNga68q4@hovoldconsulting.com> On 1/12/23 14:13, Johan Hovold wrote: > On Mon, Jan 09, 2023 at 11:13:15AM +0100, Sebastian Andrzej Siewior wrote: >> On 2022-12-27 15:56:47 [+0100], Johan Hovold wrote: >>> On Fri, Dec 16, 2022 at 12:53:38PM +0100, Marek Vasut wrote: >>>> Requesting an interrupt with IRQF_ONESHOT will run the primary handler >>>> in the hard-IRQ context even in the force-threaded mode. The >>>> force-threaded mode is used by PREEMPT_RT in order to avoid acquiring >>>> sleeping locks (spinlock_t) in hard-IRQ context. This combination >>>> makes it impossible and leads to "sleeping while atomic" warnings. >>>> >>>> Use one interrupt handler for both handlers (primary and secondary) >>>> and drop the IRQF_ONESHOT flag which is not needed. >>>> >>>> Fixes: e359b4411c283 ("serial: stm32: fix threaded interrupt handling") >>> >>> I don't think a Fixes tag is warranted as this is only needed due to >>> this undocumented quirk of PREEMPT_RT. >> >> It is not an undocumented quirk of PREEMPT_RT. The part that might not >> be well documented is that IRQF_ONESHOT won't run the primary handler as >> a threaded handler. This is also the case for IRQF_NO_THREAD and >> IRQF_PERCPU but might be more obvious. > > Yeah, that not being documented seems like an oversight as generally > drivers should not need be changed to continue working on PREEMPT_RT (or > with forced-threading generally). > >> Anyway, if the primary handler is not threaded then it runs in HARDIRQ >> context and here you must not use a spinlock_t. This is documented in >> Documentation/locking/locktypes.rst and there is also a LOCKDEP warning >> for this on !RT which is off by default because it triggers with printk >> (and this is worked on). > > All interrupt handlers typically run in hard interrupt context unless > explicitly requested to be threaded on !RT and drivers still use > spinlock_t for that so not sure how that lockdep warning is supposed to > work. Or do you mean that you have a lockdep warning specifically for > IRQF_ONESHOT primary handlers? > >>> And this should not be backported in any case. >> >> Such things have been backported via -stable in the past. If you >> disagree, please keep me in loop while is merged so I can poke people to >> backport it as part of the RT patch for the relevant kernels. > > The author did not seem to think this was stable material as there is no > cc-stable tag and it also seems fairly intrusive. The author does not have enough experience with preempt-rt to make that determination, hence deferred to Sebastian for better judgement. > But if the ST guys or whoever cares about this driver are fine with this > being backported, I don't really mind either. [...] _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
WARNING: multiple messages have this Message-ID (diff)
From: Marek Vasut <marex@denx.de> To: Johan Hovold <johan@kernel.org>, Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: linux-serial@vger.kernel.org, Alexandre Torgue <alexandre.torgue@foss.st.com>, Erwan Le Ray <erwan.leray@foss.st.com>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Jiri Slaby <jirislaby@kernel.org>, Maxime Coquelin <mcoquelin.stm32@gmail.com>, Thomas Gleixner <tglx@linutronix.de>, Valentin Caron <valentin.caron@foss.st.com>, linux-arm-kernel@lists.infradead.org, linux-stm32@st-md-mailman.stormreply.com Subject: Re: [PATCH v3] serial: stm32: Merge hard IRQ and threaded IRQ handling into single IRQ handler Date: Thu, 12 Jan 2023 17:38:48 +0100 [thread overview] Message-ID: <78e3f61f-4f87-9ac5-7c7c-172714da69d3@denx.de> (raw) In-Reply-To: <Y8AHaJIttNga68q4@hovoldconsulting.com> On 1/12/23 14:13, Johan Hovold wrote: > On Mon, Jan 09, 2023 at 11:13:15AM +0100, Sebastian Andrzej Siewior wrote: >> On 2022-12-27 15:56:47 [+0100], Johan Hovold wrote: >>> On Fri, Dec 16, 2022 at 12:53:38PM +0100, Marek Vasut wrote: >>>> Requesting an interrupt with IRQF_ONESHOT will run the primary handler >>>> in the hard-IRQ context even in the force-threaded mode. The >>>> force-threaded mode is used by PREEMPT_RT in order to avoid acquiring >>>> sleeping locks (spinlock_t) in hard-IRQ context. This combination >>>> makes it impossible and leads to "sleeping while atomic" warnings. >>>> >>>> Use one interrupt handler for both handlers (primary and secondary) >>>> and drop the IRQF_ONESHOT flag which is not needed. >>>> >>>> Fixes: e359b4411c283 ("serial: stm32: fix threaded interrupt handling") >>> >>> I don't think a Fixes tag is warranted as this is only needed due to >>> this undocumented quirk of PREEMPT_RT. >> >> It is not an undocumented quirk of PREEMPT_RT. The part that might not >> be well documented is that IRQF_ONESHOT won't run the primary handler as >> a threaded handler. This is also the case for IRQF_NO_THREAD and >> IRQF_PERCPU but might be more obvious. > > Yeah, that not being documented seems like an oversight as generally > drivers should not need be changed to continue working on PREEMPT_RT (or > with forced-threading generally). > >> Anyway, if the primary handler is not threaded then it runs in HARDIRQ >> context and here you must not use a spinlock_t. This is documented in >> Documentation/locking/locktypes.rst and there is also a LOCKDEP warning >> for this on !RT which is off by default because it triggers with printk >> (and this is worked on). > > All interrupt handlers typically run in hard interrupt context unless > explicitly requested to be threaded on !RT and drivers still use > spinlock_t for that so not sure how that lockdep warning is supposed to > work. Or do you mean that you have a lockdep warning specifically for > IRQF_ONESHOT primary handlers? > >>> And this should not be backported in any case. >> >> Such things have been backported via -stable in the past. If you >> disagree, please keep me in loop while is merged so I can poke people to >> backport it as part of the RT patch for the relevant kernels. > > The author did not seem to think this was stable material as there is no > cc-stable tag and it also seems fairly intrusive. The author does not have enough experience with preempt-rt to make that determination, hence deferred to Sebastian for better judgement. > But if the ST guys or whoever cares about this driver are fine with this > being backported, I don't really mind either. [...]
next prev parent reply other threads:[~2023-01-12 16:40 UTC|newest] Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-12-16 11:53 [PATCH v3] serial: stm32: Merge hard IRQ and threaded IRQ handling into single IRQ handler Marek Vasut 2022-12-16 11:53 ` Marek Vasut 2022-12-27 14:56 ` Johan Hovold 2022-12-27 14:56 ` Johan Hovold 2023-01-05 20:46 ` Marek Vasut 2023-01-05 20:46 ` Marek Vasut 2023-01-06 10:56 ` Johan Hovold 2023-01-06 10:56 ` Johan Hovold 2023-01-09 19:19 ` Marek Vasut 2023-01-09 19:19 ` Marek Vasut 2023-01-09 10:13 ` Sebastian Andrzej Siewior 2023-01-09 10:13 ` Sebastian Andrzej Siewior 2023-01-12 13:13 ` Johan Hovold 2023-01-12 13:13 ` Johan Hovold 2023-01-12 16:38 ` Marek Vasut [this message] 2023-01-12 16:38 ` Marek Vasut 2023-01-12 17:09 ` Johan Hovold 2023-01-12 17:09 ` Johan Hovold 2023-01-12 17:50 ` Marek Vasut 2023-01-12 17:50 ` Marek Vasut 2023-01-12 17:57 ` Johan Hovold 2023-01-12 17:57 ` Johan Hovold 2023-01-05 14:56 ` Valentin CARON 2023-01-05 14:56 ` Valentin CARON 2023-01-05 20:47 ` Marek Vasut 2023-01-05 20:47 ` Marek Vasut
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