Re: [PATCH 2/2] lockdep reentrancy

Mathieu Desnoyers
2007-01-24T16:55:07Z

Hi Andrew,

* Andrew Morton (akpm@osdl.org) wrote:
> On Tue, 16 Jan 2007 12:56:31 -0500
> Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> wrote:
>
> > Here is a patch to lockdep.c so it behaves correctly when a kprobe breakpoint is
> > put on a marker within hardirq tracing functions as long as the marker is within
> > the lockdep_recursion incremented boundaries. It should apply on
> > 2.6.20-rc4-git3.
> >
> > Mathieu
> >
> > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
> >
> >
> > @@ -1841,33 +1843,36 @@ void trace_hardirqs_on(void)
>
> You lost the patch headers.
>
> > struct task_struct *curr = current;
> > unsigned long ip;
> >
> > if (unlikely(!debug_locks || current->lockdep_recursion))
> > return;
> >
> > + current->lockdep_recursion++;
> > + barrier();
>
> Why can't we use lockdep_off() here?
>

Because I thought that changing lockdep_off() for the whole system might be a
little different than adding a lockdep recursion protection. See my other email
for the lockdep_on/off() discussion.

And please drop this patch : It sometimes make lockdep trigger false positives
under heavy IRQ load because of a dropped lockdep event.

Mathieu

> > if (DEBUG_LOCKS_WARN_ON(unlikely(!early_boot_irqs_enabled)))
> > - return;
> > + goto end;
> >
> > if (unlikely(curr->hardirqs_enabled)) {
> > debug_atomic_inc(&redundant_hardirqs_on);
> > - return;
> > + goto end;
> > }
> > /* we'll do an OFF -> ON transition: */
> > curr->hardirqs_enabled = 1;
> > ip = (unsigned long) __builtin_return_address(0);
> >
> > if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
> > - return;
> > + goto end;
> > if (DEBUG_LOCKS_WARN_ON(current->hardirq_context))
> > - return;
> > + goto end;
> > /*
> > * We are going to turn hardirqs on, so set the
> > * usage bit for all held locks:
> > */
> > if (!mark_held_locks(curr, 1, ip))
> > - return;
> > + goto end;
> > /*
> > * If we have softirqs enabled, then set the usage
> > * bit for all held locks. (disabled hardirqs prevented
> > @@ -1875,11 +1880,14 @@ void trace_hardirqs_on(void)
> > */
> > if (curr->softirqs_enabled)
> > if (!mark_held_locks(curr, 0, ip))
> > - return;
> > + goto end;
> >
> > curr->hardirq_enable_ip = ip;
> > curr->hardirq_enable_event = ++curr->irq_events;
> > debug_atomic_inc(&hardirqs_on_events);
> > +end:
> > + barrier();
> > + current->lockdep_recursion--;
>
> lockdep_on()?
>
> > }
> >
> > EXPORT_SYMBOL(trace_hardirqs_on);
> > @@ -1888,14 +1896,17 @@ void trace_hardirqs_off(void)
> > {
> > struct task_struct *curr = current;
> >
> > if (unlikely(!debug_locks || current->lockdep_recursion))
> > return;
> >
> > + current->lockdep_recursion++;
> > + barrier();
>
> lockdep_off()?
>
> > if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
> > - return;
> > + goto end;
> >
> > if (curr->hardirqs_enabled) {
> > /*
> > @@ -1910,6 +1921,9 @@ void trace_hardirqs_off(void)
> > debug_atomic_inc(&hardirqs_off_events);
> > } else
> > debug_atomic_inc(&redundant_hardirqs_off);
> > +end:
> > + barrier();
> > + current->lockdep_recursion--;
>
> lockdep_on()?

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