Patch "powerpc/rtas: Introduce rtas_get_sensor_fast() for IRQ handlers" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

powerpc/rtas: Introduce rtas_get_sensor_fast() for IRQ handlers

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
powerpc-rtas-introduce-rtas_get_sensor_fast-for-irq-handlers.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Thomas Huth <[email protected]>
Date: Fri, 17 Jul 2015 12:46:58 +0200
Subject: powerpc/rtas: Introduce rtas_get_sensor_fast() for IRQ handlers

From: Thomas Huth <[email protected]>

commit 1c2cb594441d02815d304cccec9742ff5c707495 upstream.

The EPOW interrupt handler uses rtas_get_sensor(), which in turn uses rtas_busy_delay() to wait for RTAS becoming ready in case it is necessary. But rtas_busy_delay() is annotated with might_sleep() and thus may not be used by interrupts handlers like the EPOW handler! This leads to the following BUG when CONFIG_DEBUG_ATOMIC_SLEEP is enabled:

 BUG: sleeping function called from invalid context at arch/powerpc/kernel/rtas.c:496
 in_atomic(): 1, irqs_disabled(): 1, pid: 0, name: swapper/1
 CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.2.0-rc2-thuth #6
 Call Trace:
 [c00000007ffe7b90] [c000000000807670] dump_stack+0xa0/0xdc (unreliable)
 [c00000007ffe7bc0] [c0000000000e1f14] ___might_sleep+0x134/0x180
 [c00000007ffe7c20] [c00000000002aec0] rtas_busy_delay+0x30/0xd0
 [c00000007ffe7c50] [c00000000002bde4] rtas_get_sensor+0x74/0xe0
 [c00000007ffe7ce0] [c000000000083264] ras_epow_interrupt+0x44/0x450
 [c00000007ffe7d90] [c000000000120260] handle_irq_event_percpu+0xa0/0x300
 [c00000007ffe7e70] [c000000000120524] handle_irq_event+0x64/0xc0
 [c00000007ffe7eb0] [c000000000124dbc] handle_fasteoi_irq+0xec/0x260
 [c00000007ffe7ef0] [c00000000011f4f0] generic_handle_irq+0x50/0x80
 [c00000007ffe7f20] [c000000000010f3c] __do_irq+0x8c/0x200
 [c00000007ffe7f90] [c0000000000236cc] call_do_irq+0x14/0x24
 [c00000007e6f39e0] [c000000000011144] do_IRQ+0x94/0x110
 [c00000007e6f3a30] [c000000000002594] hardware_interrupt_common+0x114/0x180

Fix this issue by introducing a new rtas_get_sensor_fast() function that does not use rtas_busy_delay() - and thus can only be used for sensors that do not cause a BUSY condition - known as "fast" sensors.

The EPOW sensor is defined to be "fast" in sPAPR - mpe.

---
 arch/powerpc/include/asm/rtas.h      |    1 +
 arch/powerpc/kernel/rtas.c           |   17 +++++++++++++++++
 arch/powerpc/platforms/pseries/ras.c |    3 ++-
 3 files changed, 20 insertions(+), 1 deletion(-)

@@ -255,6 +255,7 @@ extern void rtas_power_off(void);
 extern void rtas_halt(void);
 extern void rtas_os_term(char *str);
 extern int rtas_get_sensor(int sensor, int index, int *state);
+extern int rtas_get_sensor_fast(int sensor, int index, int *state);
 extern int rtas_get_power_level(int powerdomain, int *level);
 extern int rtas_set_power_level(int powerdomain, int level, int *setlevel);
 extern bool rtas_indicator_present(int token, int *maxindex);

@@ -584,6 +584,23 @@ int rtas_get_sensor(int sensor, int inde
 }
 EXPORT_SYMBOL(rtas_get_sensor);
 
+int rtas_get_sensor_fast(int sensor, int index, int *state)
+{
+	int token = rtas_token("get-sensor-state");
+	int rc;
+
+	if (token == RTAS_UNKNOWN_SERVICE)
+		return -ENOENT;
+
+	rc = rtas_call(token, 2, 2, state, sensor, index);
+	WARN_ON(rc == RTAS_BUSY || (rc >= RTAS_EXTENDED_DELAY_MIN &&
+				    rc <= RTAS_EXTENDED_DELAY_MAX));
+
+	if (rc < 0)
+		return rtas_error_rc(rc);
+	return rc;
+}
+
 bool rtas_indicator_present(int token, int *maxindex)
 {
 	int proplen, count, i;

@@ -187,7 +187,8 @@ static irqreturn_t ras_epow_interrupt(in
 	int state;
 	int critical;
 
-	status = rtas_get_sensor(EPOW_SENSOR_TOKEN, EPOW_SENSOR_INDEX, &state);
+	status = rtas_get_sensor_fast(EPOW_SENSOR_TOKEN, EPOW_SENSOR_INDEX,
+				      &state);
 
 	if (state > 3)
 		critical = 1;		/* Time Critical */

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/powerpc-rtas-introduce-rtas_get_sensor_fast-for-irq-handlers.patch