linux-kernel - [PATCH] lockdep: fix deadlock in lockdep_trace

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Date:	Fri, 20 Mar 2009 11:26:38 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Nick Piggin <npiggin@...e.de>,
	"lkml," <linux-kernel@...r.kernel.org>
Subject: [PATCH] lockdep: fix deadlock in lockdep_trace_alloc

Heiko pointed out that checking for irqs_disabled() after we disable
them is quite pointless..

New patch below.

---
Subject: lockdep: fix deadlock in lockdep_trace_alloc
From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Date: Fri Mar 20 11:24:21 CET 2009

Heiko reported that we grab the graph lock with irqs enabled.

Fix this by providing the same wrapper as all other lockdep entry
functions have.

Reported-by: Heiko Carstens <heiko.carstens@...ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
 kernel/lockdep.c |   21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

Index: linux-2.6/kernel/lockdep.c
===================================================================
--- linux-2.6.orig/kernel/lockdep.c
+++ linux-2.6/kernel/lockdep.c
@@ -2258,7 +2258,7 @@ void trace_softirqs_off(unsigned long ip
 		debug_atomic_inc(&redundant_softirqs_off);
 }
 
-void lockdep_trace_alloc(gfp_t gfp_mask)
+static void __lockdep_trace_alloc(gfp_t gfp_mask)
 {
 	struct task_struct *curr = current;
 
@@ -2277,10 +2277,27 @@ void lockdep_trace_alloc(gfp_t gfp_mask)
 	if (!(gfp_mask & __GFP_FS))
 		return;
 
+	mark_held_locks(curr, RECLAIM_FS);
+}
+
+static void check_flags(unsigned long flags);
+
+void lockdep_trace_alloc(gfp_t gfp_mask)
+{
+	unsigned long flags;
+
+	if (unlikely(current->lockdep_recursion))
+		return;
+
 	if (DEBUG_LOCKS_WARN_ON(irqs_disabled()))
 		return;
 
-	mark_held_locks(curr, RECLAIM_FS);
+	raw_local_irq_save(flags);
+	check_flags(flags);
+	current->lockdep_recursion = 1;
+	__lockdep_trace_alloc(gfp_mask);
+	current->lockdep_recursion = 0;
+	raw_local_irq_restore(flags);
 }
 
 static int mark_irqflags(struct task_struct *curr, struct held_lock *hlock)

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