On Mon, Sep 14, 2020 at 05:45:09PM +0100, Tvrtko Ursulin wrote:
>
> On 23/07/2020 18:21, Chris Wilson wrote:
> > Since the debugfs may peek into the GEM contexts as the corresponding
> > client/fd is being closed, we may try and follow a dangling pointer.
> > However, the context closure itself is serialised with the ctx->mutex,
> > so if we hold that mutex as we inspect the state coupled in the context,
> > we know the pointers within the context are stable and will remain valid
> > as we inspect their tables.
> >
> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > Cc: CQ Tang <cq.tang@xxxxxxxxx>
> > Cc: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > ---
> > drivers/gpu/drm/i915/i915_debugfs.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> > index 784219962193..ea469168cd44 100644
> > --- a/drivers/gpu/drm/i915/i915_debugfs.c
> > +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> > @@ -326,6 +326,7 @@ static void print_context_stats(struct seq_file *m,
> > }
> > i915_gem_context_unlock_engines(ctx);
> > + mutex_lock(&ctx->mutex);
> > if (!IS_ERR_OR_NULL(ctx->file_priv)) {
> > struct file_stats stats = {
> > .vm = rcu_access_pointer(ctx->vm),
> > @@ -346,6 +347,7 @@ static void print_context_stats(struct seq_file *m,
> > print_file_stats(m, name, stats);
> > }
> > + mutex_unlock(&ctx->mutex);
> > spin_lock(&i915->gem.contexts.lock);
> > list_safe_reset_next(ctx, cn, link);
> >
>
> Hm this apparently never got it's r-b and so got re-discovered in the field.
> +Nikunj
>
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
I'm not super thrilled about patch 1 in this, for debugfs imo better to
wrangle this in the driver. And without patch 1 and 2 this wont fix a
whole lot.
-Daniel
>
> Regards,
>
> Tvrtko
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
