> -----Original Message----- > From: Andy Shevchenko [mailto:andy.shevchenko@xxxxxxxxx] > Sent: Tuesday, March 16, 2021 10:41 PM > To: Johan Hovold <johan@xxxxxxxxxx>; Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx>; > Song Bao Hua (Barry Song) <song.bao.hua@xxxxxxxxxxxxx> > Cc: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxxxxx>; Greg > Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>; Jiri Slaby <jirislaby@xxxxxxxxxx>; > linux-arm Mailing List <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>; Linux Samsung > SOC <linux-samsung-soc@xxxxxxxxxxxxxxx>; open list:SERIAL DRIVERS > <linux-serial@xxxxxxxxxxxxxxx>; Linux Kernel Mailing List > <linux-kernel@xxxxxxxxxxxxxxx>; Hector Martin <marcan@xxxxxxxxx>; Arnd > Bergmann <arnd@xxxxxxxxxx> > Subject: Re: [PATCH] tty: serial: samsung_tty: remove spinlock flags in > interrupt handlers > > On Tue, Mar 16, 2021 at 11:02 AM Johan Hovold <johan@xxxxxxxxxx> wrote: > > > > On Mon, Mar 15, 2021 at 07:12:12PM +0100, Krzysztof Kozlowski wrote: > > > Since interrupt handler is called with disabled local interrupts, there > > > is no need to use the spinlock primitives disabling interrupts as well. > > > > This isn't generally true due to "threadirqs" and that can lead to > > deadlocks if the console code is called from hard irq context. > > > > Now, this is *not* the case for this particular driver since it doesn't > > even bother to take the port lock in console_write(). That should > > probably be fixed instead. > > > > See https://lore.kernel.org/r/X7kviiRwuxvPxC8O@localhost. > > Finn, Barry, something to check I think? My understanding is that spin_lock_irqsave can't protect the context the console_write() is called in hardirq for threaded_irq case mainly for preempt-rt scenarios as spin_lock_irqsave doesn't disable irq in that case at all. See: https://www.kernel.org/doc/html/latest/locking/locktypes.html spinlock_t and PREEMPT_RT On a PREEMPT_RT kernel spinlock_t is mapped to a separate implementation based on rt_mutex which changes the semantics: Preemption is not disabled. The hard interrupt related suffixes for spin_lock / spin_unlock operations (_irq, _irqsave / _irqrestore) do not affect the CPU’s interrupt disabled state. So if console_write() can interrupt our code in hardirq, we should move to raw_spin_lock_irqsave for this driver. I think it is almost always wrong to call spin_lock_irqsave in hardirq. > > -- > With Best Regards, > Andy Shevchenko Thanks Barry
