> -----Original Message----- > From: Andy Shevchenko [mailto:[email protected]] > Sent: Tuesday, March 16, 2021 10:41 PM > To: Johan Hovold <[email protected]>; Finn Thain <[email protected]>; > Song Bao Hua (Barry Song) <[email protected]> > Cc: Krzysztof Kozlowski <[email protected]>; Greg > Kroah-Hartman <[email protected]>; Jiri Slaby <[email protected]>; > linux-arm Mailing List <[email protected]>; Linux Samsung > SOC <[email protected]>; open list:SERIAL DRIVERS > <[email protected]>; Linux Kernel Mailing List > <[email protected]>; Hector Martin <[email protected]>; Arnd > Bergmann <[email protected]> > Subject: Re: [PATCH] tty: serial: samsung_tty: remove spinlock flags in > interrupt handlers > > On Tue, Mar 16, 2021 at 11:02 AM Johan Hovold <[email protected]> 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
