Messages in this thread | | | From | "Song Bao Hua (Barry Song)" <> | Subject | RE: [PATCH] tty: serial: samsung_tty: remove spinlock flags in interrupt handlers | Date | Fri, 19 Mar 2021 06:36:39 +0000 |
| |
> -----Original Message----- > From: Andy Shevchenko [mailto:andy.shevchenko@gmail.com] > Sent: Tuesday, March 16, 2021 10:41 PM > To: Johan Hovold <johan@kernel.org>; Finn Thain <fthain@telegraphics.com.au>; > Song Bao Hua (Barry Song) <song.bao.hua@hisilicon.com> > Cc: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>; Greg > Kroah-Hartman <gregkh@linuxfoundation.org>; Jiri Slaby <jirislaby@kernel.org>; > linux-arm Mailing List <linux-arm-kernel@lists.infradead.org>; Linux Samsung > SOC <linux-samsung-soc@vger.kernel.org>; open list:SERIAL DRIVERS > <linux-serial@vger.kernel.org>; Linux Kernel Mailing List > <linux-kernel@vger.kernel.org>; Hector Martin <marcan@marcan.st>; Arnd > Bergmann <arnd@kernel.org> > 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@kernel.org> 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
| |