tty: serial: msm: Fix lock init issue with earlycon
Subsystems (2)
PATCH 1/1 tty: serial: msm: Fix lock init issue with earlycon
With CONFIG_DEBUG_SPINLOCK enabled we see:
BUG: spinlock bad magic on CPU#0, swapper/0 lock: early_console_dev+0x8/0x160, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0 CPU: 0 PID: 0 Comm: swapper Not tainted 3.17.0-09733-gb446b33-dirty #18 Call trace: [<c0087ba0>] dump_backtrace+0x0/0x140 [<c0087cf0>] show_stack+0x10/0x1c [<c0598be0>] dump_stack+0x74/0xb8 [<c00cb720>] spin_dump+0x78/0x88 [<c00cb754>] spin_bug+0x24/0x34 [<c00cb7e4>] do_raw_spin_lock+0x30/0x158 [<c059ea2c>] _raw_spin_lock+0x1c/0x2c [<c02e0e30>] __msm_console_write+0x68/0x154 [<c02e0f50>] msm_serial_early_write_dm+0x14/0x20 [<c00cf040>] call_console_drivers.constprop.23+0xa4/0xc4 [<c00d00c4>] console_unlock+0x2a8/0x330 [<c00d121c>] register_console+0x26c/0x338 [<c0805af4>] setup_earlycon+0x2c0/0x300 [<c0805c48>] msm_serial_dm_setup_earlycon+0x18/0x24 [<c07ed158>] do_early_param+0x84/0xd0 [<c00aec18>] parse_args+0x2b4/0x3ec [<c07ed588>] parse_early_options+0x2c/0x38 [<c07ed5c8>] parse_early_param+0x34/0x50 [<c07f03c0>] setup_arch+0x290/0x604 [<c07ed67c>] start_kernel+0x94/0x38c
As the earlycon write function for msm requires a lock, we need to init it as part of the setup call.
--- drivers/tty/serial/msm_serial.c | 4 ++++ 1 file changed, 4 insertions(+)
drivers/tty/serial/msm_serial.c +4 -0
@@ -973,6 +973,8 @@ msm_serial_early_console_setup(struct earlycon_device *device, const char *opt)if (!device->port.membase)return -ENODEV ; +spin_lock_init (&device->port.lock); + device->con->write = msm_serial_early_write;return 0 ; }
@@ -995,6 +997,8 @@ msm_serial_early_console_setup_dm(struct earlycon_device *device,if (!device->port.membase)return -ENODEV ; +spin_lock_init (&device->port.lock); + device->con->write = msm_serial_early_write_dm;return 0 ; }
Signature · 3 lines
Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project
Quoted 5 lines · Kumar Gala
With
CONFIG_DEBUG_SPINLOCKenabled we see:BUG: spinlock bad magic on CPU#0, swapper/0 lock: early_console_dev+0x8/0x160, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0 CPU: 0 PID: 0 Comm: swapper Not tainted 3.17.0-09733-gb446b33-dirty #18
[...]
Quoted 14 lines
drivers/tty/serial/msm_serial.c +2
-0@@ -973,6 +973,8 @@ msm_serial_early_console_setup(struct earlycon_device *device, const char *opt)if (!device->port.membase)return -ENODEV ; +spin_lock_init (&device->port.lock); + device->con->write = msm_serial_early_write;return 0 ; }
drivers/tty/serial/msm_serial.c msm_serial_early_console_setup_dm(struct earlycon_device *device, · line 1004
Quoted 8 lines
drivers/tty/serial/msm_serial.c +2
-0@@ -995,6 +997,8 @@ msm_serial_early_console_setup_dm(struct earlycon_device *device,if (!device->port.membase)return -ENODEV ; +spin_lock_init (&device->port.lock); + device->con->write = msm_serial_early_write_dm;return 0 ; }
Could this be done in the tty core instead?
Signature · 2 lines
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
Quoted 23 lines · Stephen Boyd
Quoted 5 lines · Kumar Gala
With
CONFIG_DEBUG_SPINLOCKenabled we see:BUG: spinlock bad magic on CPU#0, swapper/0 lock: early_console_dev+0x8/0x160, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0 CPU: 0 PID: 0 Comm: swapper Not tainted 3.17.0-09733-gb446b33-dirty #18[...]
Quoted 14 lines
drivers/tty/serial/msm_serial.c +1
-0@@ -973,6 +973,8 @@ msm_serial_early_console_setup(struct earlycon_device *device, const char *opt)if (!device->port.membase)return -ENODEV ; +spin_lock_init (&device->port.lock); + device->con->write = msm_serial_early_write;return 0 ; }@@ -995,6 +997,8 @@ msm_serial_early_console_setup_dm(struct earlycon_device *device,if (!device->port.membase)
Quoted 8 lines
drivers/tty/serial/msm_serial.c msm_serial_early_console_setup_dm(struct earlycon_device *device, · line 1004
Quoted 6 lines
drivers/tty/serial/msm_serial.c +1
-0return -ENODEV ; +spin_lock_init (&device->port.lock); + device->con->write = msm_serial_early_write_dm;return 0 ; }Could this be done in the tty core instead?
Or even better: refactor __msm_console_write() so no spin_lock() is required for the earlycon write.
FWIW, __msm_console_write() is a deadlock-waiting-to_happen since it does not disable interrupts with spin_lock_irqsave().
Regards,
Peter Hurley
Quoted 33 lines · Peter Hurley
Quoted 23 lines · Stephen Boyd
Quoted 5 lines · Kumar Gala
With
CONFIG_DEBUG_SPINLOCKenabled we see:BUG: spinlock bad magic on CPU#0, swapper/0 lock: early_console_dev+0x8/0x160, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0 CPU: 0 PID: 0 Comm: swapper Not tainted 3.17.0-09733-gb446b33-dirty #18[...]
Quoted 14 lines
drivers/tty/serial/msm_serial.c +1
-0@@ -973,6 +973,8 @@ msm_serial_early_console_setup(struct earlycon_device *device, const char *opt)if (!device->port.membase)return -ENODEV ; +spin_lock_init (&device->port.lock); + device->con->write = msm_serial_early_write;return 0 ; }@@ -995,6 +997,8 @@ msm_serial_early_console_setup_dm(struct earlycon_device *device,if (!device->port.membase)Quoted 8 lines
drivers/tty/serial/msm_serial.c msm_serial_early_console_setup_dm(struct earlycon_device *device, · line 1004
Quoted 6 lines
drivers/tty/serial/msm_serial.c +1
-0return -ENODEV ; +spin_lock_init (&device->port.lock); + device->con->write = msm_serial_early_write_dm;return 0 ; }Could this be done in the tty core instead?
Quoted 2 lines
Or even better: refactor
__msm_console_write()so nospin_lock()is required for the earlycon write.
Can't we keep the early console forever with keep_bootcon? In which case we may want to prevent things from trampling on each other? I don't see how the lock will help us here though because the port isn't even the same between the earlycon and the ttyMSM console. Removing the lock from the earlycon path is probably easier than caring about this debugging scenario.
Quoted 4 lines
FWIW,
__msm_console_write()is a deadlock-waiting-to_happen since it does not disable interrupts withspin_lock_irqsave().
Yeah we should fix that. As far as I can tell we've never used the irqsave variant of the lock in the console path. Did this become necessary at some point since this driver was introduced? I'm wondering how many stable trees need the fix.
Signature · 2 lines
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
Quoted 10 lines · Stephen Boyd
Quoted 4 lines · Peter Hurley
FWIW,
__msm_console_write()is a deadlock-waiting-to_happen since it does not disable interrupts withspin_lock_irqsave().Yeah we should fix that. As far as I can tell we've never used the irqsave variant of the lock in the console path. Did this become necessary at some point since this driver was introduced? I'm wondering how many stable trees need the fix.
Actually I don't see this case. It looks like the console is always called in call_console_drivers() with irqs saved and disabled via the logbuf_lock in console_cont_flush() or console_unlock().
Signature · 2 lines
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
Quoted 12 lines · Stephen Boyd
Quoted 10 lines · Stephen Boyd
Quoted 4 lines · Peter Hurley
FWIW,
__msm_console_write()is a deadlock-waiting-to_happen since it does not disable interrupts withspin_lock_irqsave().Yeah we should fix that. As far as I can tell we've never used the irqsave variant of the lock in the console path. Did this become necessary at some point since this driver was introduced? I'm wondering how many stable trees need the fix.
Quoted 4 lines
Actually I don't see this case. It looks like the console is always called in
call_console_drivers()with irqs saved and disabled via thelogbuf_lockinconsole_cont_flush()orconsole_unlock().
Thanks for bringing that to my attention.
That looks like a vestige of the initial transition away from BKL. I might look into just disabling preemption; even that might not really be necessary.
Regards,
Peter Hurley