This is a note to let you know that I've just added the patch titled
drm/vc4: Fix race between page flip completion event and clean-up
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
drm-vc4-fix-race-between-page-flip-completion-event-and-clean-up.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 26fc78f6fef39b9d7a15def5e7e9826ff68303f4 Mon Sep 17 00:00:00 2001
From: Derek Foreman <derekf@xxxxxxxxxxxxxxx>
Date: Thu, 24 Nov 2016 12:11:55 -0600
Subject: drm/vc4: Fix race between page flip completion event and clean-up
From: Derek Foreman <derekf@xxxxxxxxxxxxxxx>
commit 26fc78f6fef39b9d7a15def5e7e9826ff68303f4 upstream.
There was a small window where a userspace program could submit
a pageflip after receiving a pageflip completion event yet still
receive EBUSY.
Signed-off-by: Derek Foreman <derekf@xxxxxxxxxxxxxxx>
Signed-off-by: Eric Anholt <eric@xxxxxxxxxx>
Reviewed-by: Eric Anholt <eric@xxxxxxxxxx>
Reviewed-by: Daniel Stone <daniels@xxxxxxxxxxxxx>
Cc: Amit Pundir <amit.pundir@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/vc4/vc4_crtc.c | 8 ++++++++
drivers/gpu/drm/vc4/vc4_drv.h | 1 +
drivers/gpu/drm/vc4/vc4_kms.c | 33 +++++++++++++++++++++++++--------
3 files changed, 34 insertions(+), 8 deletions(-)
--- a/drivers/gpu/drm/vc4/vc4_crtc.c
+++ b/drivers/gpu/drm/vc4/vc4_crtc.c
@@ -669,6 +669,14 @@ void vc4_disable_vblank(struct drm_devic
CRTC_WRITE(PV_INTEN, 0);
}
+/* Must be called with the event lock held */
+bool vc4_event_pending(struct drm_crtc *crtc)
+{
+ struct vc4_crtc *vc4_crtc = to_vc4_crtc(crtc);
+
+ return !!vc4_crtc->event;
+}
+
static void vc4_crtc_handle_page_flip(struct vc4_crtc *vc4_crtc)
{
struct drm_crtc *crtc = &vc4_crtc->base;
--- a/drivers/gpu/drm/vc4/vc4_drv.h
+++ b/drivers/gpu/drm/vc4/vc4_drv.h
@@ -440,6 +440,7 @@ int vc4_bo_stats_debugfs(struct seq_file
extern struct platform_driver vc4_crtc_driver;
int vc4_enable_vblank(struct drm_device *dev, unsigned int crtc_id);
void vc4_disable_vblank(struct drm_device *dev, unsigned int crtc_id);
+bool vc4_event_pending(struct drm_crtc *crtc);
int vc4_crtc_debugfs_regs(struct seq_file *m, void *arg);
int vc4_crtc_get_scanoutpos(struct drm_device *dev, unsigned int crtc_id,
unsigned int flags, int *vpos, int *hpos,
--- a/drivers/gpu/drm/vc4/vc4_kms.c
+++ b/drivers/gpu/drm/vc4/vc4_kms.c
@@ -119,17 +119,34 @@ static int vc4_atomic_commit(struct drm_
/* Make sure that any outstanding modesets have finished. */
if (nonblock) {
- ret = down_trylock(&vc4->async_modeset);
- if (ret) {
+ struct drm_crtc *crtc;
+ struct drm_crtc_state *crtc_state;
+ unsigned long flags;
+ bool busy = false;
+
+ /*
+ * If there's an undispatched event to send then we're
+ * obviously still busy. If there isn't, then we can
+ * unconditionally wait for the semaphore because it
+ * shouldn't be contended (for long).
+ *
+ * This is to prevent a race where queuing a new flip
+ * from userspace immediately on receipt of an event
+ * beats our clean-up and returns EBUSY.
+ */
+ spin_lock_irqsave(&dev->event_lock, flags);
+ for_each_crtc_in_state(state, crtc, crtc_state, i)
+ busy |= vc4_event_pending(crtc);
+ spin_unlock_irqrestore(&dev->event_lock, flags);
+ if (busy) {
kfree(c);
return -EBUSY;
}
- } else {
- ret = down_interruptible(&vc4->async_modeset);
- if (ret) {
- kfree(c);
- return ret;
- }
+ }
+ ret = down_interruptible(&vc4->async_modeset);
+ if (ret) {
+ kfree(c);
+ return ret;
}
ret = drm_atomic_helper_prepare_planes(dev, state);
Patches currently in stable-queue which might be from derekf@xxxxxxxxxxxxxxx are
queue-4.9/drm-vc4-fix-race-between-page-flip-completion-event-and-clean-up.patch