Re: [PATCH] lockdep: fix deadlock in lockdep_trace_alloc

From: Peter Zijlstra
Date: Fri Mar 20 2009 - 09:45:39 EST


On Fri, 2009-03-20 at 14:07 +0100, Heiko Carstens wrote:
> On Fri, 20 Mar 2009 11:26:38 +0100
> Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> > 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@xxxxxxxxx>
> > 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@xxxxxxxxxx>
> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> > ---
> > 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);
>
> Hmm... still not working:

Its Friday for sure... :/

Actually reading the code helps, we should only do that IRQ check if its
a __GFP_FS allocation -- those should never be done with IRQs disabled.

So we need to pass the flags down and fudge in that.

---
Subject: lockdep: fix deadlock in lockdep_trace_alloc
From: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
---
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, unsigned long flags)
{
struct task_struct *curr = current;

@@ -2277,12 +2277,29 @@ void lockdep_trace_alloc(gfp_t gfp_mask)
if (!(gfp_mask & __GFP_FS))
return;

- if (DEBUG_LOCKS_WARN_ON(irqs_disabled()))
+ if (DEBUG_LOCKS_WARN_ON(raw_irqs_disabled_flags(flags)))
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;
+
+ raw_local_irq_save(flags);
+ check_flags(flags);
+ current->lockdep_recursion = 1;
+ __lockdep_trace_alloc(gfp_mask, flags);
+ 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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