On Thu, Sep 04, 2014 at 08:17:42AM +0100, Chris Wilson wrote:
> On Thu, Sep 04, 2014 at 09:11:23AM +0200, Daniel Vetter wrote:
> > In
> >
> > commit 1f83fee08d625f8d0130f9fe5ef7b17c2e022f3c
> > Author: Daniel Vetter <daniel.vetter@xxxxxxxx>
> > Date: Thu Nov 15 17:17:22 2012 +0100
> >
> > drm/i915: clear up wedged transitions
> >
> > I've accidentally inverted the EIO/wedged handling in the fault
> > handler: We want to return the EIO as a SIGBUS only if it's not
> > because of the gpu having died, to prevent userspace from unduly
> > dying.
> >
> > In my defence the comment right above is completely misleading, so fix
> > both.
> >
> > v2: Drop the WARN_ON, it's not actually a bug to e.g. receive an -EIO
> > when swap-in fails.
>
> You mean drop the WARN_ON and the if...
>
> > Reported-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/i915_gem.c | 9 ++++++---
> > 1 file changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> > index 6c685708a516..247ad18b8c3e 100644
> > --- a/drivers/gpu/drm/i915/i915_gem.c
> > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > @@ -1596,9 +1596,12 @@ unlock:
> > out:
> > switch (ret) {
> > case -EIO:
> > - /* If this -EIO is due to a gpu hang, give the reset code a
> > - * chance to clean up the mess. Otherwise return the proper
> > - * SIGBUS. */
> > + /*
> > + * We eat errors when the gpu is terminally wedged to avoid
> > + * userspace unduly crashing (gl has no provisions for mmaps to
> > + * fail). But any other -EIO isn't ours (e.g. swap in failure)
> > + * and so needs to be reported.
> > + */
> > if (i915_terminally_wedged(&dev_priv->gpu_error)) {
>
> Because you didn't actually make the change you set out to do :)
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 377d619827bb..b11fbe9332d5 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1541,23 +1541,21 @@ unlock:
mutex_unlock(&dev->struct_mutex);
out:
switch (ret) {
- case -EIO:
- /* If this -EIO is due to a gpu hang, give the reset code a
- * chance to clean up the mess. Otherwise return the proper
- * SIGBUS. */
- if (!i915_terminally_wedged(&dev_priv->gpu_error)) {
- ret = VM_FAULT_SIGBUS;
- break;
- }
+ case 0:
+ /*
+ * Success. You may proceed.
+ */
case -EAGAIN:
/*
* EAGAIN means the gpu is hung and we'll wait for the error
* handler to reset everything when re-faulting in
* i915_mutex_lock_interruptible.
*/
- case 0:
case -ERESTARTSYS:
case -EINTR:
+ /* Signal interruptus. Return to userspace and await
+ * further instructions.
+ */
case -EBUSY:
/*
* EBUSY is ok: this just means that another thread
@@ -1568,6 +1566,20 @@ out:
case -ENOMEM:
ret = VM_FAULT_OOM;
break;
+ case -EIO:
+ /* The driver should never report an EIO due to GPU hangs,
+ * all requests shold have been reset and the object should
+ * be idle. There should be no impediment for us to mmap the
+ * object in those cases. It would be nice if we could throw
+ * a warning in such cases, but...
+ *
+ * EIO can also arise from a failure to swap in pages,
+ * for example. Here, we must report SIGBUS as there is
+ * no recovery for memory corruption.
+ *
+ * And since we can have a wedged GPU and swap failure,
+ * having a WARN here could be misleading.
+ */
case -ENOSPC:
case -EFAULT:
ret = VM_FAULT_SIGBUS;
--
Chris Wilson, Intel Open Source Technology Centre
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