From: dillon min <dillon.minfei@gmail.com> To: Erwan LE RAY <erwan.leray@foss.st.com> Cc: Greg KH <gregkh@linuxfoundation.org>, linux-serial@vger.kernel.org, Alexandre TORGUE <alexandre.torgue@foss.st.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Maxime Coquelin <mcoquelin.stm32@gmail.com>, jirislaby@kernel.org, linux-stm32@st-md-mailman.stormreply.com, Linux ARM <linux-arm-kernel@lists.infradead.org>, Fabrice Gasnier <fabrice.gasnier@foss.st.com>, Valentin Caron <valentin.caron@foss.st.com> Subject: Re: [Linux-stm32] [PATCH] serial: stm32: optimize spin lock usage Date: Mon, 12 Apr 2021 21:41:53 +0800 [thread overview] Message-ID: <CAL9mu0LnxD69Y2F_TK_b+N5QhMS6bjz6YU-zJdscY75S3jj8qQ@mail.gmail.com> (raw) In-Reply-To: <f3985d70-4f00-7442-de4e-e382b19e3e50@foss.st.com> On 4/12/21, Erwan LE RAY <erwan.leray@foss.st.com> wrote: > Hi Dillon, > > Thanks for your patch. > > Could you please elaborate the use case in your commit message ? Sorry, local_irq_save() plus spin_lock() same to spin_lock_irqsave() There is no deadlock . Please ignore this patch. Thanks Dillon > > Best Regards, Erwan. > > On 4/12/21 10:54 AM, dillon min wrote: >> Hi Greg, >> >> On Mon, Apr 12, 2021 at 4:25 PM Greg KH <gregkh@linuxfoundation.org> >> wrote: >>> >>> On Mon, Apr 12, 2021 at 02:50:20PM +0800, dillon min wrote: >>>> Hi Greg, >>>> >>>> Thanks for the quick response, please ignore the last private mail. >>>> >>>> On Mon, Apr 12, 2021 at 1:52 PM Greg KH <gregkh@linuxfoundation.org> >>>> wrote: >>>>> >>>>> On Mon, Apr 12, 2021 at 12:34:21PM +0800, dillon.minfei@gmail.com >>>>> wrote: >>>>>> From: dillon min <dillon.minfei@gmail.com> >>>>>> >>>>>> To avoid potential deadlock in spin_lock usage, change to use >>>>>> spin_lock_irqsave(), spin_unlock_irqrestore() in process(thread_fn) >>>>>> context. >>>>>> spin_lock(), spin_unlock() under handler context. >>>>>> >>>>>> remove unused local_irq_save/restore call. >>>>>> >>>>>> Signed-off-by: dillon min <dillon.minfei@gmail.com> >>>>>> --- >>>>>> Was verified on stm32f469-disco board. need more test on stm32mp >>>>>> platform. >>>>>> >>>>>> drivers/tty/serial/stm32-usart.c | 27 +++++++++++++++++---------- >>>>>> 1 file changed, 17 insertions(+), 10 deletions(-) >>>>>> >>>>>> diff --git a/drivers/tty/serial/stm32-usart.c >>>>>> b/drivers/tty/serial/stm32-usart.c >>>>>> index b3675cf25a69..c4c859b34367 100644 >>>>>> --- a/drivers/tty/serial/stm32-usart.c >>>>>> +++ b/drivers/tty/serial/stm32-usart.c >>>>>> @@ -214,7 +214,7 @@ static void stm32_usart_receive_chars(struct >>>>>> uart_port *port, bool threaded) >>>>>> struct tty_port *tport = &port->state->port; >>>>>> struct stm32_port *stm32_port = to_stm32_port(port); >>>>>> const struct stm32_usart_offsets *ofs = >>>>>> &stm32_port->info->ofs; >>>>>> - unsigned long c; >>>>>> + unsigned long c, flags; >>>>>> u32 sr; >>>>>> char flag; >>>>>> >>>>>> @@ -276,9 +276,17 @@ static void stm32_usart_receive_chars(struct >>>>>> uart_port *port, bool threaded) >>>>>> uart_insert_char(port, sr, USART_SR_ORE, c, flag); >>>>>> } >>>>>> >>>>>> - spin_unlock(&port->lock); >>>>>> + if (threaded) >>>>>> + spin_unlock_irqrestore(&port->lock, flags); >>>>>> + else >>>>>> + spin_unlock(&port->lock); >>>>> >>>>> You shouldn't have to check for this, see the other patches on the >>>>> list >>>>> recently that fixed this up to not be an issue for irq handlers. >>>> Can you help to give more hints, or the commit id of the patch which >>>> fixed this. thanks. >>>> >>>> I'm still confused with this. >>>> >>>> The stm32_usart_threaded_interrupt() is a kthread context, once >>>> port->lock holds by this function, another serial interrupts raised, >>>> such as USART_SR_TXE,stm32_usart_interrupt() can't get the lock, >>>> there will be a deadlock. isn't it? >>>> >>>> So, shouldn't I use spin_lock{_irqsave} according to the caller's >>>> context ? >>> >>> Please see 81e2073c175b ("genirq: Disable interrupts for force threaded >>> handlers") for when threaded irq handlers have irqs disabled, isn't that >>> the case you are trying to "protect" from here? >>> >>> Why is the "threaded" flag used at all? The driver should not care. >>> >>> Also see 9baedb7baeda ("serial: imx: drop workaround for forced irq >>> threading") in linux-next for an example of how this was fixed up in a >>> serial driver. >>> >>> does that help? >>> >> Yes, it's really helpful. and 81e2073c175b should be highlighted in a >> doc. >> In my past knowledge, we should care about hard irq & thread_fn lock >> conflict. >> This patch has totally avoided patching code in the separate driver side. >> thanks. >> >> I will just keep the changes in stm32_usart_console_write(), remove >> these code in >> thread_fn. update version 2 for you. >> >> thanks. >> >> Dillon, >>> thanks, >>> >>> greg k-h >> _______________________________________________ >> Linux-stm32 mailing list >> Linux-stm32@st-md-mailman.stormreply.com >> https://st-md-mailman.stormreply.com/mailman/listinfo/linux-stm32 >> >
WARNING: multiple messages have this Message-ID (diff)
From: dillon min <dillon.minfei@gmail.com> To: Erwan LE RAY <erwan.leray@foss.st.com> Cc: Greg KH <gregkh@linuxfoundation.org>, linux-serial@vger.kernel.org, Alexandre TORGUE <alexandre.torgue@foss.st.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Maxime Coquelin <mcoquelin.stm32@gmail.com>, jirislaby@kernel.org, linux-stm32@st-md-mailman.stormreply.com, Linux ARM <linux-arm-kernel@lists.infradead.org>, Fabrice Gasnier <fabrice.gasnier@foss.st.com>, Valentin Caron <valentin.caron@foss.st.com> Subject: Re: [Linux-stm32] [PATCH] serial: stm32: optimize spin lock usage Date: Mon, 12 Apr 2021 21:41:53 +0800 [thread overview] Message-ID: <CAL9mu0LnxD69Y2F_TK_b+N5QhMS6bjz6YU-zJdscY75S3jj8qQ@mail.gmail.com> (raw) In-Reply-To: <f3985d70-4f00-7442-de4e-e382b19e3e50@foss.st.com> On 4/12/21, Erwan LE RAY <erwan.leray@foss.st.com> wrote: > Hi Dillon, > > Thanks for your patch. > > Could you please elaborate the use case in your commit message ? Sorry, local_irq_save() plus spin_lock() same to spin_lock_irqsave() There is no deadlock . Please ignore this patch. Thanks Dillon > > Best Regards, Erwan. > > On 4/12/21 10:54 AM, dillon min wrote: >> Hi Greg, >> >> On Mon, Apr 12, 2021 at 4:25 PM Greg KH <gregkh@linuxfoundation.org> >> wrote: >>> >>> On Mon, Apr 12, 2021 at 02:50:20PM +0800, dillon min wrote: >>>> Hi Greg, >>>> >>>> Thanks for the quick response, please ignore the last private mail. >>>> >>>> On Mon, Apr 12, 2021 at 1:52 PM Greg KH <gregkh@linuxfoundation.org> >>>> wrote: >>>>> >>>>> On Mon, Apr 12, 2021 at 12:34:21PM +0800, dillon.minfei@gmail.com >>>>> wrote: >>>>>> From: dillon min <dillon.minfei@gmail.com> >>>>>> >>>>>> To avoid potential deadlock in spin_lock usage, change to use >>>>>> spin_lock_irqsave(), spin_unlock_irqrestore() in process(thread_fn) >>>>>> context. >>>>>> spin_lock(), spin_unlock() under handler context. >>>>>> >>>>>> remove unused local_irq_save/restore call. >>>>>> >>>>>> Signed-off-by: dillon min <dillon.minfei@gmail.com> >>>>>> --- >>>>>> Was verified on stm32f469-disco board. need more test on stm32mp >>>>>> platform. >>>>>> >>>>>> drivers/tty/serial/stm32-usart.c | 27 +++++++++++++++++---------- >>>>>> 1 file changed, 17 insertions(+), 10 deletions(-) >>>>>> >>>>>> diff --git a/drivers/tty/serial/stm32-usart.c >>>>>> b/drivers/tty/serial/stm32-usart.c >>>>>> index b3675cf25a69..c4c859b34367 100644 >>>>>> --- a/drivers/tty/serial/stm32-usart.c >>>>>> +++ b/drivers/tty/serial/stm32-usart.c >>>>>> @@ -214,7 +214,7 @@ static void stm32_usart_receive_chars(struct >>>>>> uart_port *port, bool threaded) >>>>>> struct tty_port *tport = &port->state->port; >>>>>> struct stm32_port *stm32_port = to_stm32_port(port); >>>>>> const struct stm32_usart_offsets *ofs = >>>>>> &stm32_port->info->ofs; >>>>>> - unsigned long c; >>>>>> + unsigned long c, flags; >>>>>> u32 sr; >>>>>> char flag; >>>>>> >>>>>> @@ -276,9 +276,17 @@ static void stm32_usart_receive_chars(struct >>>>>> uart_port *port, bool threaded) >>>>>> uart_insert_char(port, sr, USART_SR_ORE, c, flag); >>>>>> } >>>>>> >>>>>> - spin_unlock(&port->lock); >>>>>> + if (threaded) >>>>>> + spin_unlock_irqrestore(&port->lock, flags); >>>>>> + else >>>>>> + spin_unlock(&port->lock); >>>>> >>>>> You shouldn't have to check for this, see the other patches on the >>>>> list >>>>> recently that fixed this up to not be an issue for irq handlers. >>>> Can you help to give more hints, or the commit id of the patch which >>>> fixed this. thanks. >>>> >>>> I'm still confused with this. >>>> >>>> The stm32_usart_threaded_interrupt() is a kthread context, once >>>> port->lock holds by this function, another serial interrupts raised, >>>> such as USART_SR_TXE,stm32_usart_interrupt() can't get the lock, >>>> there will be a deadlock. isn't it? >>>> >>>> So, shouldn't I use spin_lock{_irqsave} according to the caller's >>>> context ? >>> >>> Please see 81e2073c175b ("genirq: Disable interrupts for force threaded >>> handlers") for when threaded irq handlers have irqs disabled, isn't that >>> the case you are trying to "protect" from here? >>> >>> Why is the "threaded" flag used at all? The driver should not care. >>> >>> Also see 9baedb7baeda ("serial: imx: drop workaround for forced irq >>> threading") in linux-next for an example of how this was fixed up in a >>> serial driver. >>> >>> does that help? >>> >> Yes, it's really helpful. and 81e2073c175b should be highlighted in a >> doc. >> In my past knowledge, we should care about hard irq & thread_fn lock >> conflict. >> This patch has totally avoided patching code in the separate driver side. >> thanks. >> >> I will just keep the changes in stm32_usart_console_write(), remove >> these code in >> thread_fn. update version 2 for you. >> >> thanks. >> >> Dillon, >>> thanks, >>> >>> greg k-h >> _______________________________________________ >> Linux-stm32 mailing list >> Linux-stm32@st-md-mailman.stormreply.com >> https://st-md-mailman.stormreply.com/mailman/listinfo/linux-stm32 >> > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-04-12 13:41 UTC|newest] Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-04-12 4:34 [PATCH] serial: stm32: optimize spin lock usage dillon.minfei 2021-04-12 4:34 ` dillon.minfei 2021-04-12 5:52 ` Greg KH 2021-04-12 5:52 ` Greg KH 2021-04-12 6:50 ` dillon min 2021-04-12 6:50 ` dillon min 2021-04-12 8:25 ` Greg KH 2021-04-12 8:25 ` Greg KH 2021-04-12 8:54 ` dillon min 2021-04-12 8:54 ` dillon min 2021-04-12 13:19 ` [Linux-stm32] " Erwan LE RAY 2021-04-12 13:19 ` Erwan LE RAY 2021-04-12 13:41 ` dillon min [this message] 2021-04-12 13:41 ` dillon min 2021-04-12 7:23 ` kernel test robot 2021-04-12 7:23 ` kernel test robot 2021-04-12 7:23 ` kernel test robot 2021-04-12 7:29 ` dillon min 2021-04-12 7:29 ` dillon min 2021-04-12 7:29 ` dillon min
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