Messages in this thread | | | From | Sergey Senozhatsky <> | Date | Thu, 2 Jul 2020 14:40:33 +0900 | Subject | Re: UART/TTY console deadlock |
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On (20/07/02 14:12), Sergey Senozhatsky wrote: > Date: Thu, 2 Jul 2020 14:12:13 +0900 > From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> > To: Tony Lindgren <tony@atomide.com> > Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, Petr Mladek > <pmladek@suse.com>, Andy Shevchenko <andy.shevchenko@gmail.com>, Raul > Rangel <rrangel@google.com>, Sergey Senozhatsky > <sergey.senozhatsky.work@gmail.com>, linux-kernel > <linux-kernel@vger.kernel.org>, Greg Kroah-Hartman > <gregkh@linuxfoundation.org>, Andy Shevchenko > <andriy.shevchenko@linux.intel.com>, kurt@linutronix.de, "S, Shirish" > <Shirish.S@amd.com>, Peter Zijlstra <peterz@infradead.org>, John Ogness > <john.ogness@linutronix.de>, Steven Rostedt <rostedt@goodmis.org> > Subject: Re: UART/TTY console deadlock > Message-ID: <20200702051213.GB3450@jagdpanzerIV.localdomain> > > On (20/06/30 11:02), Tony Lindgren wrote: > > This conditional disable for irq_shared does not look nice to me > > from the other device point of view :) > > > > Would it be possible to just set up te dummy interrupt handler > > for the startup, then change it back afterwards? See for example > > omap8250_no_handle_irq(). > > I think we can do it. serial8250_do_startup() and irq handler take > port->lock, so they should be synchronized.
Hmm, hold on. Why does it disable IRQ in the first place? IRQ handlers should grab the port->lock. So if there is already running IRQ, then serial8250_do_startup() will wait until IRQ handler unlocks the port->lock. If serial8250_do_startup() grabs the port->lock first, then IRQ will wait for serial8250_do_startup() to unlock it. serial8250_do_startup() does not release the port->unlock until its done:
spin_lock_irqsave(&port->lock, flags);
wait_for_xmitr(up, UART_LSR_THRE); serial_port_out_sync(port, UART_IER, UART_IER_THRI); udelay(1); /* allow THRE to set */ iir1 = serial_port_in(port, UART_IIR); serial_port_out(port, UART_IER, 0); serial_port_out_sync(port, UART_IER, UART_IER_THRI); udelay(1); /* allow a working UART time to re-assert THRE */ iir = serial_port_in(port, UART_IIR); serial_port_out(port, UART_IER, 0);
spin_unlock_irqrestore(&port->lock, flags);
so IRQ will not see the inconsistent device state.
What exactly is the purpose of disable_irq_nosync()? Can we just remove disable_irq_nosync()/enable_irq() instead? Are there any IRQ handlers that don't acquire the port->lock?
-ss
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