On Fri, 2010-09-24 at 15:30 -0500, Jason Wessel wrote: > Jiri, > > Can you try this simple patch which is attached? > > > > On 09/24/2010 01:04 PM, Jiri Olsa wrote: > > while starting kgdb early debug on latest tip tree, > > I got SIGSEGV inside kernel in following location: > > > > > [clip] > > I found out it's due to foolowing commit, that's causing the init code > > to be called without the ctx field being defined... > > > > commit c3f00c70276d8ae82578c8b773e2db657f69a478 > > Author: Peter Zijlstra <[email protected]> > > Date: Wed Aug 18 14:37:15 2010 +0200 > > > > > > > > I took a look at the tip core, and the ctx parameter is no longer passed > into the perf_event_alloc() from perf_event_create_kernel_counter() kgdb > no longer gets it filled in for free. > > The reality is that kgdb never had a true context or a way to mark the > hw breakpoint as a kernel only context for the hw breakpoint > reservations. The patch is only a short term fix perhaps until on of > the perf guys explains the right way to use it. :-)
Argh, yes, its using the ctx rather early.. we cannot have a context before we've initialized the event, and here it looks like hw_breakpoint wants to use the context to initialize the event, chick, egg, etc.. Frederic, anything we can do about that? > differences between files attachment > (0001-Fix-null-dereference-when-using-early-kgdb.patch) > From 17f3febd001a26aee9a75c61152b60b7e0ae1ea9 Mon Sep 17 00:00:00 2001 > From: Jason Wessel <[email protected]> > Date: Fri, 24 Sep 2010 15:21:11 -0500 > Subject: [PATCH] Fix null dereference when using early kgdb > > Signed-off-by: Jason Wessel <[email protected]> > --- > kernel/hw_breakpoint.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/kernel/hw_breakpoint.c b/kernel/hw_breakpoint.c > index 3b714e8..3c7ccdf 100644 > --- a/kernel/hw_breakpoint.c > +++ b/kernel/hw_breakpoint.c > @@ -213,7 +213,7 @@ toggle_bp_slot(struct perf_event *bp, bool enable, enum > bp_type_idx type, > int weight) > { > int cpu = bp->cpu; > - struct task_struct *tsk = bp->ctx->task; > + struct task_struct *tsk = bp->ctx ? bp->ctx->task : NULL; > > /* Pinned counter cpu profiling */ > if (!tsk) { That'll probably screw over some accounting, not sure what tsk is used for there. ------------------------------------------------------------------------------ Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev _______________________________________________ Kgdb-bugreport mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/kgdb-bugreport
