linux-kernel - [PATCH] softirq/preempt: add missing current->preempt_disable

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Date:	Mon, 24 Nov 2014 15:16:19 +0100
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] softirq/preempt: add missing current->preempt_disable_ip
 update

While debugging some "sleeping function called from invalid context" bug I
realized that the debug message "Preemption disabled at:" pointed to an
incorrect function.
In particular if the function/action that disabled preemption was
spin_lock_bh() then current->preempt_disable_ip won't be updated.

The reason for this is that __local_bh_disable_ip() will increase
preempt_count manually instead of calling preempt_count_add(), which
would handle the update correctly.
It look like the manual handling was done to work around some lockdep issue.

So add the missing update of current->preempt_disable_ip to
__local_bh_disable_ip() as well.

Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
---
 kernel/softirq.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/softirq.c b/kernel/softirq.c
index 501baa9ac1be..edd51027e3ab 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -114,8 +114,13 @@ void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
 		trace_softirqs_off(ip);
 	raw_local_irq_restore(flags);

-	if (preempt_count() == cnt)
-		trace_preempt_off(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));
+	if (preempt_count() == cnt) {
+		unsigned long ip = get_parent_ip(CALLER_ADDR1);
+#ifdef CONFIG_DEBUG_PREEMPT
+		current->preempt_disable_ip = ip;
+#endif
+		trace_preempt_off(CALLER_ADDR0, ip);
+	}
 }
 EXPORT_SYMBOL(__local_bh_disable_ip);
 #endif /* CONFIG_TRACE_IRQFLAGS */
-- 
1.8.5.5

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