From: Hans-Joachim Picht <hpicht@redhat.com>
Date: Thu, 6 Nov 2008 15:43:29 +0100
Subject: [s390] sclp: incorrect softirq disable/enable
Message-id: 20081106144329.GB12027@redhat.com
O-Subject: [RHEL5 U4 PATCH 2/4] s390 - sclp: Incorrect softirq disable/enable.
Bugzilla: 468021
RH-Acked-by: Pete Zaitcev <zaitcev@redhat.com>

Description
============

The user might see a warning like
BUG: warning at kernel/softirq.c:121/_local_bh_enable()
followed by a kernel stackstrace.

When a lot of printks are done in interrupt context the sclp
console driver calls local_bh_enable()/_local_bh_enable() to
prevent softirq execution. Calling _local_bh_enable() from
interrupt context triggers a warning.

Since softirqs are disabled anyway when in interrupt context,
just add a check in which context the kernel is presently and
only call local_bh_disable()/_local_bh_enable() when on process
context.

Bugzilla
=========

BZ 468021
https://bugzilla.redhat.com/show_bug.cgi?id=468021

Upstream status of the patch:
=============================

Fixed upstream with git commit c59d744bd8a0e283daf6726881e4c9aa4bd2526.
First kernel which has this fixed is 2.6.21.

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=c59d744bd8a0e283daf6726881e4c9aa4bd25261

Test status:
============

The patch has been tested and fixes the problem.
The fix has been verified by the IBM test department.

Please ACK.

With best regards,

	--Hans

diff --git a/drivers/s390/char/sclp.c b/drivers/s390/char/sclp.c
index 86aaad1..d5b67ee 100644
--- a/drivers/s390/char/sclp.c
+++ b/drivers/s390/char/sclp.c
@@ -414,6 +414,7 @@ sclp_sync_wait(void)
 	unsigned long flags;
 	unsigned long cr0, cr0_sync;
 	u64 timeout;
+	int irq_context;
 
 	/* We'll be disabling timer interrupts, so we need a custom timeout
 	 * mechanism */
@@ -426,7 +427,9 @@ sclp_sync_wait(void)
 	}
 	local_irq_save(flags);
 	/* Prevent bottom half from executing once we force interrupts open */
-	local_bh_disable();
+	irq_context = in_interrupt();
+	if (!irq_context)
+		local_bh_disable();
 	/* Enable service-signal interruption, disable timer interrupts */
 	trace_hardirqs_on();
 	__ctl_store(cr0, 0, 0);
@@ -448,7 +451,8 @@ sclp_sync_wait(void)
 	}
 	local_irq_disable();
 	__ctl_load(cr0, 0, 0);
-	_local_bh_enable();
+	if (!irq_context)
+		_local_bh_enable();
 	local_irq_restore(flags);
 }