From: peterz@infradead.org
To: Will Deacon <will@kernel.org>
Cc: gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org,
linux@armlinux.org.uk, linux-arm-kernel@lists.infradead.org,
andre.przywara@arm.com
Subject: Re: lockdep splat ("possible circular locking dependency detected") with PL011 on 5.8
Date: Tue, 11 Aug 2020 12:38:41 +0200 [thread overview]
Message-ID: <20200811103841.GC2674@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200811101313.GA6970@willie-the-truck>
On Tue, Aug 11, 2020 at 11:13:13AM +0100, Will Deacon wrote:
> Hi,
>
> Using magic-sysrq via a keyboard interrupt over the serial console results in
> the following lockdep splat with the PL011 UART driver on v5.8. I can reproduce
> the issue under QEMU with arm64 defconfig + PROVE_LOCKING.
>
> Any chance somebody could take a look, please? It's a little annoying,
> because it means when I uses magic-sysrq to increase the loglevel prior
> to testing something else, lockdep gets disabled as a result.
>
Going by msm_serial, the thing to do is something like this:
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;
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-08-11 10:40 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-11 10:13 lockdep splat ("possible circular locking dependency detected") with PL011 on 5.8 Will Deacon
2020-08-11 10:38 ` peterz [this message]
2020-08-11 11:17 ` Will Deacon
2020-08-11 12:36 ` Will Deacon
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200811103841.GC2674@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=andre.przywara@arm.com \
--cc=gregkh@linuxfoundation.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux@armlinux.org.uk \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).