Messages in this thread | | | Date | Tue, 11 Aug 2020 13:36:58 +0100 | From | Will Deacon <> | Subject | Re: lockdep splat ("possible circular locking dependency detected") with PL011 on 5.8 |
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On Tue, Aug 11, 2020 at 12:17:13PM +0100, Will Deacon wrote: > On Tue, Aug 11, 2020 at 12:38:41PM +0200, peterz@infradead.org wrote: > > diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c > > index 8efd7c2a34fe..1717790ece2b 100644 > > --- a/drivers/tty/serial/amba-pl011.c > > +++ b/drivers/tty/serial/amba-pl011.c > > @@ -308,8 +308,9 @@ static void pl011_write(unsigned int val, const struct uart_amba_port *uap, > > */ > > static int pl011_fifo_to_tty(struct uart_amba_port *uap) > > { > > - u16 status; > > unsigned int ch, flag, fifotaken; > > + int sysrq; > > + u16 status; > > > > for (fifotaken = 0; fifotaken != 256; fifotaken++) { > > status = pl011_read(uap, REG_FR); > > @@ -344,10 +345,12 @@ static int pl011_fifo_to_tty(struct uart_amba_port *uap) > > flag = TTY_FRAME; > > } > > > > - if (uart_handle_sysrq_char(&uap->port, ch & 255)) > > - continue; > > + spin_unlock(&uap->port.lock); > > + sysrq = uart_handle_sysrq_char(&uap->port, ch & 255); > > + spin_lock(&uap->port.lock); > > > > - uart_insert_char(&uap->port, ch, UART011_DR_OE, ch, flag); > > + if (!sysrq) > > + uart_insert_char(&uap->port, ch, UART011_DR_OE, ch, flag); > > } > > > > return fifotaken; > > Cheers, that seems to do the trick: > > Tested-by: Will Deacon <will@kernel.org> > > but what I don't understand is why I haven't run into this before, and why > nobody else seems to be reporting it! > > I'll try some older kernels to see if it ever worked.
I tried 5.4, 4.19, 4.14 and 4.9:
5.4 and 4.19 have the lockdep splat
4.14 doesn't have the splat, yet I don't see why (the driver code hasn't really changed)
4.9 magic sysrq doesn't work at all (no splat either though)
Will
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