Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161788AbaKNSBH (ORCPT ); Fri, 14 Nov 2014 13:01:07 -0500 Received: from mail-lb0-f180.google.com ([209.85.217.180]:37723 "EHLO mail-lb0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161460AbaKNSBE (ORCPT ); Fri, 14 Nov 2014 13:01:04 -0500 From: Rabin Vincent To: Greg Kroah-Hartman Cc: Ingo Molnar , bigeasy@linutronix.de, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Rabin Vincent Subject: [PATCH] serial: 8250: don't attempt a trylock if in sysrq Date: Fri, 14 Nov 2014 19:00:41 +0100 Message-Id: <1415988041-6124-1-git-send-email-rabin@rab.in> X-Mailer: git-send-email 2.1.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Attempting to use SysRq via the 8250 serial port with spin lock debugging on on a uniprocessor system results in the following splat: SysRq : BUG: spinlock trylock failure on UP on CPU#0, swapper/0 lock: serial8250_ports+0x0/0x8c0, .magic: dead4ead, .owner: swapper/0, .owner_cpu: 0 CPU: 0 PID: 0 Comm: swapper Not tainted 3.18.0-rc4+ #37 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.7.5-20140531_083030-gandalf 04/01/2014 ffffffff8245ba00 ffffffff81628b28 ffffffff812c8d27 ffffffff81628b48 ffffffff8106812e ffffffff8245ba00 ffffffff814e22ed ffffffff81628b68 ffffffff810681a6 0000000000000000 0000000000000000 ffffffff81628b88 Call Trace: [] dump_stack+0x19/0x1b [] spin_dump+0x7e/0xd0 [] spin_bug+0x26/0x30 [] do_raw_spin_trylock+0x4c/0x60 [] _raw_spin_trylock+0x1d/0x60 [] serial8250_console_write+0x68/0x190 [] ? sprintf+0x40/0x50 [] call_console_drivers.constprop.11+0x9e/0xf0 [] console_unlock+0x3e6/0x490 [] vprintk_emit+0x275/0x530 [] printk+0x4d/0x4f [] __handle_sysrq+0x62/0x1b0 [] ? __handle_sysrq+0x5/0x1b0 [] handle_sysrq+0x26/0x30 [] serial8250_rx_chars+0x1d7/0x250 [] serial8250_handle_irq+0x7b/0x90 [] serial8250_default_handle_irq+0x23/0x30 [] serial8250_interrupt+0x63/0xe0 [] handle_irq_event_percpu+0x4e/0x200 [] handle_irq_event+0x41/0x70 [] ? handle_edge_irq+0x1e/0x110 [] handle_edge_irq+0x9e/0x110 [] handle_irq+0x22/0x40 [] do_IRQ+0x4e/0xf0 [] common_interrupt+0x6d/0x6d [] ? default_idle+0x1f/0xd0 [] ? default_idle+0x1d/0xd0 [] arch_cpu_idle+0xf/0x20 [] cpu_startup_entry+0x25b/0x360 [] rest_init+0xbe/0xd0 [] start_kernel+0x339/0x346 [] x86_64_start_reservations+0x2a/0x2c [] x86_64_start_kernel+0xf2/0xf6 HELP : loglevel(0-9) reboot(b) crash(c) show-all-locks(d) te... Before ebade5e833eda30 ("serial: 8250: Clean up the locking for -rt") this was handled by not even attempting to try the lock if port->sysrq, since it is known to be taken by the interrupt handler; see https://bugzilla.kernel.org/show_bug.cgi?id=6716#c1. Restore that behavior. Signed-off-by: Rabin Vincent --- drivers/tty/serial/8250/8250_core.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c index ca5cfdc..aec51eb 100644 --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -3198,7 +3198,9 @@ serial8250_console_write(struct console *co, const char *s, unsigned int count) serial8250_rpm_get(up); - if (port->sysrq || oops_in_progress) + if (port->sysrq) + locked = 0; + else if (oops_in_progress) locked = spin_trylock_irqsave(&port->lock, flags); else spin_lock_irqsave(&port->lock, flags); -- 2.1.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/