On Sat, Jul 14, 2012 at 10:55:19AM +0100, Chris Wilson wrote: > On Fri, 13 Jul 2012 17:37:14 +0200, Daniel Vetter <daniel at ffwll.ch> wrote: > > On Fri, Jul 13, 2012 at 02:14:05PM +0100, Chris Wilson wrote: > > > Otherwise we end up trying to unpin a freed object and BUG. > > > > > > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk> > > > Cc: Ben Widawsky <ben at bwidawsk.net> > > > > Afact this patch contains quite some code refactoring that does not > > relate directly to the fix (or if it does, I fail to see the direct > > relevance). So I think this either needs an explanation in the commit > > message or be put into a separate patch (I agree though for actual code > > cleanups). > > > > For the fix itself I seem to be a bit dense again - the only thing I see > > is that you move the refcount handling into do_switch. Afacs we do the > > ref-handling in both cases only when do_switch is successful, and also > > right at the end of do_switch (or right afterwards). So can you please > > enlighten your clueless maintainer a bit an explain how things blow up? > > The fix is that the reference handling was only done on one path, not > both. Hence the default_ctx ends up being used-after-free. > > The rest of it was just unwinding the code to get to finding the bug... Yeah, I've figured this out somewhat later yesterday. Still, a bugfix shouldn't resemble a riddle more than a simple patch ... Afacs we only need to move the reference count handling from i915_switch_context to do_switch (and mention in the commit message that it's been missing when creating the default context). -Daniel -- Daniel Vetter Mail: daniel at ffwll.ch Mobile: +41 (0)79 365 57 48
