Re: lockdep splat ("possible circular locking dependency detected") with PL011 on 5.8
From: Will Deacon <will@kernel.org>
Date: 2020-08-11 12:37:07
Also in:
lkml
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:quoted
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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel