From: Rob Clark <[email protected]>
DRM_MODESET_LOCK_ALL_BEGIN() has a hidden trap-door (aka retry loop),
which means we can't rely too much on variable initializers.
Fixes: 6e455f5dcdd1 ("drm/crtc: fix uninitialized variable use")
Signed-off-by: Rob Clark <[email protected]>
---
I have mixed feelings about DRM_MODESET_LOCK_ALL_BEGIN() (and friends)
magic. On one hand it simplifies the deadlock/back dance. OTOH it
conceals a nasty sharp edge. Maybe it is better to have the complicated
restart path a bit more explicit, like it was originally.
drivers/gpu/drm/drm_crtc.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index cb90e70d85e8..65f9f66933bb 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -904,6 +904,7 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
connector_set = NULL;
fb = NULL;
mode = NULL;
+ num_connectors = 0;
DRM_MODESET_LOCK_ALL_END(dev, ctx, ret);
--
2.43.0
On Mon, Feb 12, 2024 at 1:55 PM Rob Clark <[email protected]> wrote:
>
> From: Rob Clark <[email protected]>
>
> DRM_MODESET_LOCK_ALL_BEGIN() has a hidden trap-door (aka retry loop),
> which means we can't rely too much on variable initializers.
>
> Fixes: 6e455f5dcdd1 ("drm/crtc: fix uninitialized variable use")
> Signed-off-by: Rob Clark <[email protected]>
> ---
> I have mixed feelings about DRM_MODESET_LOCK_ALL_BEGIN() (and friends)
> magic. On one hand it simplifies the deadlock/back dance. OTOH it
> conceals a nasty sharp edge. Maybe it is better to have the complicated
> restart path a bit more explicit, like it was originally.
I should also point out, had drm-misc-next been using gitlab MRs and
gitlab CI, we would have caught this ;-)
BR,
-R
> drivers/gpu/drm/drm_crtc.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> index cb90e70d85e8..65f9f66933bb 100644
> --- a/drivers/gpu/drm/drm_crtc.c
> +++ b/drivers/gpu/drm/drm_crtc.c
> @@ -904,6 +904,7 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
> connector_set = NULL;
> fb = NULL;
> mode = NULL;
> + num_connectors = 0;
>
> DRM_MODESET_LOCK_ALL_END(dev, ctx, ret);
>
> --
> 2.43.0
>
On 2/12/2024 1:55 PM, Rob Clark wrote:
> From: Rob Clark <[email protected]>
>
> DRM_MODESET_LOCK_ALL_BEGIN() has a hidden trap-door (aka retry loop),
> which means we can't rely too much on variable initializers.
>
> Fixes: 6e455f5dcdd1 ("drm/crtc: fix uninitialized variable use")
> Signed-off-by: Rob Clark <[email protected]>
> ---
> I have mixed feelings about DRM_MODESET_LOCK_ALL_BEGIN() (and friends)
> magic. On one hand it simplifies the deadlock/back dance. OTOH it
> conceals a nasty sharp edge. Maybe it is better to have the complicated
> restart path a bit more explicit, like it was originally.
>
> drivers/gpu/drm/drm_crtc.c | 1 +
> 1 file changed, 1 insertion(+)
>
Nice catch !!
Reviewed-by: Abhinav Kumar <[email protected]>
On Mon, 12 Feb 2024 at 23:55, Rob Clark <[email protected]> wrote:
>
> From: Rob Clark <[email protected]>
>
> DRM_MODESET_LOCK_ALL_BEGIN() has a hidden trap-door (aka retry loop),
> which means we can't rely too much on variable initializers.
>
> Fixes: 6e455f5dcdd1 ("drm/crtc: fix uninitialized variable use")
> Signed-off-by: Rob Clark <[email protected]>
> ---
> I have mixed feelings about DRM_MODESET_LOCK_ALL_BEGIN() (and friends)
> magic. On one hand it simplifies the deadlock/back dance. OTOH it
> conceals a nasty sharp edge. Maybe it is better to have the complicated
> restart path a bit more explicit, like it was originally.
>
> drivers/gpu/drm/drm_crtc.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> index cb90e70d85e8..65f9f66933bb 100644
> --- a/drivers/gpu/drm/drm_crtc.c
> +++ b/drivers/gpu/drm/drm_crtc.c
> @@ -904,6 +904,7 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
> connector_set = NULL;
> fb = NULL;
> mode = NULL;
> + num_connectors = 0;
Nit: I think we should move all this next to the
DRM_MODESET_LOCK_ALL_BEGIN() and drop initialisation from the prologue
of the function, but it's definitely a separate and more intrusive
story.
Reviewed-by: Dmitry Baryshkov <[email protected]>
> DRM_MODESET_LOCK_ALL_END(dev, ctx, ret);
--
With best wishes
Dmitry
On Tue, 13 Feb 2024 at 15:50, Dmitry Baryshkov
<[email protected]> wrote:
>
> On Mon, 12 Feb 2024 at 23:55, Rob Clark <[email protected]> wrote:
> >
> > From: Rob Clark <[email protected]>
> >
> > DRM_MODESET_LOCK_ALL_BEGIN() has a hidden trap-door (aka retry loop),
> > which means we can't rely too much on variable initializers.
> >
> > Fixes: 6e455f5dcdd1 ("drm/crtc: fix uninitialized variable use")
> > Signed-off-by: Rob Clark <[email protected]>
> > ---
> > I have mixed feelings about DRM_MODESET_LOCK_ALL_BEGIN() (and friends)
> > magic. On one hand it simplifies the deadlock/back dance. OTOH it
> > conceals a nasty sharp edge. Maybe it is better to have the complicated
> > restart path a bit more explicit, like it was originally.
> >
> > drivers/gpu/drm/drm_crtc.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> > index cb90e70d85e8..65f9f66933bb 100644
> > --- a/drivers/gpu/drm/drm_crtc.c
> > +++ b/drivers/gpu/drm/drm_crtc.c
> > @@ -904,6 +904,7 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
> > connector_set = NULL;
> > fb = NULL;
> > mode = NULL;
> > + num_connectors = 0;
>
> Nit: I think we should move all this next to the
> DRM_MODESET_LOCK_ALL_BEGIN() and drop initialisation from the prologue
> of the function, but it's definitely a separate and more intrusive
> story.
>
> Reviewed-by: Dmitry Baryshkov <[email protected]>
After running this through CI:
Tested-by: Dmitry Baryshkov <[email protected]> #sc7180, sdm845
> > DRM_MODESET_LOCK_ALL_END(dev, ctx, ret);
>
>
> --
> With best wishes
> Dmitry
--
With best wishes
Dmitry
On Mon, Feb 12, 2024 at 01:55:34PM -0800, Rob Clark wrote:
> From: Rob Clark <[email protected]>
>
> DRM_MODESET_LOCK_ALL_BEGIN() has a hidden trap-door (aka retry loop),
> which means we can't rely too much on variable initializers.
>
> Fixes: 6e455f5dcdd1 ("drm/crtc: fix uninitialized variable use")
> Signed-off-by: Rob Clark <[email protected]>
Cc: [email protected]
I guess at least ...
> ---
> I have mixed feelings about DRM_MODESET_LOCK_ALL_BEGIN() (and friends)
> magic. On one hand it simplifies the deadlock/back dance. OTOH it
> conceals a nasty sharp edge. Maybe it is better to have the complicated
> restart path a bit more explicit, like it was originally.
Alternative would be a very magic for {} macro, but those tend to get
easily defeated with goto/break and friends. Maybe it works now that
linux/cleanup.h has landed, but I'm not sure it's actually better and not
just trading one set of sharp edges for another. Worth a shot in a
prototype at least, if someone's bored.
>
> drivers/gpu/drm/drm_crtc.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> index cb90e70d85e8..65f9f66933bb 100644
> --- a/drivers/gpu/drm/drm_crtc.c
> +++ b/drivers/gpu/drm/drm_crtc.c
> @@ -904,6 +904,7 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
> connector_set = NULL;
> fb = NULL;
> mode = NULL;
> + num_connectors = 0;
I think it'd be neater to have all these right below the
DRM_MODESET_LOCK_A_BEGIN instead of duplicated here and at the beginning
of the function. But it's a bit a bikeshed and in some cases (when you use
it later on) gcc might get pissed too. So either way:
Reviewed-by: Daniel Vetter <[email protected]>
Cheers, Sima
>
> DRM_MODESET_LOCK_ALL_END(dev, ctx, ret);
>
> --
> 2.43.0
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
On Mon, 12 Feb 2024 13:55:34 -0800, Rob Clark wrote:
> DRM_MODESET_LOCK_ALL_BEGIN() has a hidden trap-door (aka retry loop),
> which means we can't rely too much on variable initializers.
>
>
Applied to drm-misc-fixes, thanks!
[1/1] drm/crtc: fix uninitialized variable use even harder
commit: b6802b61a9d0e99dcfa6fff7c50db7c48a9623d3
Best regards,
--
Dmitry Baryshkov <[email protected]>