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SubjectRe: rb tree hrtimer lockup bug (found by perf_fuzzer)
On Wed, 19 Mar 2014, Vince Weaver wrote:
> On Wed, 19 Mar 2014, Thomas Gleixner wrote:
>
> > On Wed, 19 Mar 2014, Vince Weaver wrote:
> > > On Tue, 18 Mar 2014, Thomas Gleixner wrote:
> > > your patch didn't seem to print anything additional the first time throug.
> > >
> > > I then tried the trace command you suggested, but I'm getting an empty
> > > ftrace buffer which possibly means I don't have enough ftrace kernel
> > > options enabled.
> > >
> > > Here's the most recent boot crash.
> > >
> > > [ 5.367069] ODEBUG: Info active (active state 0) object type: timer_list hint: (null)
> >
> > Stupid me. We get the hint from the wreckaged object ....
> >
> > A hopefully better approach is the delta patch below.
>
> with that applied on top:
>
> [ 5.342681] Invalid timer base: tmr ffff880117740150 tmr->base (null) base ffff880118618000
> [ 5.352786] ------------[ cut here ]------------
> [ 5.357911] WARNING: CPU: 4 PID: 0 at lib/debugobjects.c:260 debug_print_object+0x8c/0xb0()
> [ 5.367023] ODEBUG: Info active (active state 0) object type: timer_list hint: (null) delayed_work_timer_fn+0x0/0x20

Good, we have at least a point where we can gather useful
information. The timer belongs to a delayed work. The work itself is
tracked via debug objects as well. So we can get that as well. Delta
patch below.

Thanks,

tglx
------

Index: linux-2.6/lib/debugobjects.c
===================================================================
--- linux-2.6.orig/lib/debugobjects.c
+++ linux-2.6/lib/debugobjects.c
@@ -14,6 +14,7 @@
#include <linux/debugfs.h>
#include <linux/slab.h>
#include <linux/hash.h>
+#include <linux/workqueue.h>

#define ODEBUG_HASH_BITS 14
#define ODEBUG_HASH_SIZE (1 << ODEBUG_HASH_BITS)
@@ -400,6 +401,20 @@ void debug_object_info(void *addr, struc
debug_print_object(obj, "Info");

raw_spin_unlock_irqrestore(&db->lock, flags);
+
+ addr = container_of(addr, struct delayed_work, timer);
+
+ db = get_bucket((unsigned long) addr);
+
+ raw_spin_lock_irqsave(&db->lock, flags);
+
+ obj = lookup_object(addr, db);
+ if (!obj)
+ pr_err("Object unknown %p\n", addr);
+ else
+ debug_print_object(obj, "Info");
+
+ raw_spin_unlock_irqrestore(&db->lock, flags);
}

/**
@@ -452,6 +467,7 @@ int debug_object_activate(void *addr, st
}
if (!obj->hint)
obj->hint = descr->debug_hint ? descr->debug_hint(addr) : NULL;
+
raw_spin_unlock_irqrestore(&db->lock, flags);
return ret;
}





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