On Wed, Jun 24, 2020 at 07:03:09PM -0400, Lyude Paul wrote:
This got me confused for a bit while looking over this code: I had been planning on adding some blocking function calls into this function, but seeing the irqsave/irqrestore variants of spin_(un)lock() didn't make it very clear whether or not that would actually be safe.
So I went ahead and reviewed every single driver in the kernel that uses this function, and they all fall into three categories:
- Driver probe code
- ->atomic_disable() callbacks
- Legacy modesetting callbacks
All of these will be guaranteed to have IRQs enabled, which means it's perfectly safe to block here. Just to make things a little less confusing to others in the future, let's switch over to spin_lock_irq()/spin_unlock_irq() to make that fact a little more obvious.
Signed-off-by: Lyude Paul lyude@redhat.com Cc: Daniel Vetter daniel@ffwll.ch Cc: Ville Syrjälä ville.syrjala@linux.intel.com
I think the patch is correct, but now we're having a bit a inconsistency, since all other functions where the same applies still use _irqsave. I looked through the file and I think drm_vblank_get, drm_crtc_vblank_reset, drm_crtc_vblank_on and drm_legacy_vblank_post_modeset, drm_queue_vblank_event and drm_crtc_queue_sequence_ioctl are all candiates for the same cleanup.
Maybe follow up patches for less confusion?
On this:
Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch
drivers/gpu/drm/drm_vblank.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c index ce5c1e1d29963..e895f5331fdb4 100644 --- a/drivers/gpu/drm/drm_vblank.c +++ b/drivers/gpu/drm/drm_vblank.c @@ -1283,13 +1283,12 @@ void drm_crtc_vblank_off(struct drm_crtc *crtc) struct drm_pending_vblank_event *e, *t;
ktime_t now;
unsigned long irqflags; u64 seq;
if (drm_WARN_ON(dev, pipe >= dev->num_crtcs)) return;
spin_lock_irqsave(&dev->event_lock, irqflags);
spin_lock_irq(&dev->event_lock);
spin_lock(&dev->vbl_lock); drm_dbg_vbl(dev, "crtc %d, vblank enabled %d, inmodeset %d\n",
@@ -1325,7 +1324,7 @@ void drm_crtc_vblank_off(struct drm_crtc *crtc) drm_vblank_put(dev, pipe); send_vblank_event(dev, e, seq, now); }
- spin_unlock_irqrestore(&dev->event_lock, irqflags);
spin_unlock_irq(&dev->event_lock);
/* Will be reset by the modeset helpers when re-enabling the crtc by
- calling drm_calc_timestamping_constants(). */
-- 2.26.2