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authorRabin Vincent <rabin@rab.in>2014-11-14 19:00:41 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-11-25 17:06:40 -0800
commit6fad18fa51392c9847a4e3a95134b2e57155e563 (patch)
tree9e3fbe4761771ea5658691462cc3b79749cd4836 /drivers/tty
parent3ffb1a8193bead7bf4ef0fec2dae050c70e4c1c1 (diff)
downloadlinux-6fad18fa51392c9847a4e3a95134b2e57155e563.tar.bz2
serial: 8250: don't attempt a trylock if in sysrq
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: <IRQ> [<ffffffff812c8d27>] dump_stack+0x19/0x1b [<ffffffff8106812e>] spin_dump+0x7e/0xd0 [<ffffffff810681a6>] spin_bug+0x26/0x30 [<ffffffff8106843c>] do_raw_spin_trylock+0x4c/0x60 [<ffffffff812cdb1d>] _raw_spin_trylock+0x1d/0x60 [<ffffffff812336d8>] serial8250_console_write+0x68/0x190 [<ffffffff811eb0b0>] ? sprintf+0x40/0x50 [<ffffffff8106ab5e>] call_console_drivers.constprop.11+0x9e/0xf0 [<ffffffff8106b276>] console_unlock+0x3e6/0x490 [<ffffffff8106b595>] vprintk_emit+0x275/0x530 [<ffffffff812c869a>] printk+0x4d/0x4f [<ffffffff8121e612>] __handle_sysrq+0x62/0x1b0 [<ffffffff8121e5b5>] ? __handle_sysrq+0x5/0x1b0 [<ffffffff8121ebc6>] handle_sysrq+0x26/0x30 [<ffffffff81233157>] serial8250_rx_chars+0x1d7/0x250 [<ffffffff812338bb>] serial8250_handle_irq+0x7b/0x90 [<ffffffff812338f3>] serial8250_default_handle_irq+0x23/0x30 [<ffffffff812318b3>] serial8250_interrupt+0x63/0xe0 [<ffffffff8106d80e>] handle_irq_event_percpu+0x4e/0x200 [<ffffffff8106da01>] handle_irq_event+0x41/0x70 [<ffffffff810701ee>] ? handle_edge_irq+0x1e/0x110 [<ffffffff8107026e>] handle_edge_irq+0x9e/0x110 [<ffffffff810041c2>] handle_irq+0x22/0x40 [<ffffffff812d096e>] do_IRQ+0x4e/0xf0 [<ffffffff812cf4ed>] common_interrupt+0x6d/0x6d <EOI> [<ffffffff8100acbf>] ? default_idle+0x1f/0xd0 [<ffffffff8100acbd>] ? default_idle+0x1d/0xd0 [<ffffffff8100b61f>] arch_cpu_idle+0xf/0x20 [<ffffffff8105c1db>] cpu_startup_entry+0x25b/0x360 [<ffffffff812c726e>] rest_init+0xbe/0xd0 [<ffffffff816a4dcb>] start_kernel+0x339/0x346 [<ffffffff816a4495>] x86_64_start_reservations+0x2a/0x2c [<ffffffff816a4589>] 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 <rabin@rab.in> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty')
-rw-r--r--drivers/tty/serial/8250/8250_core.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index d0d0c3b6af02..9515924b7f38 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -3191,7 +3191,9 @@ 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);