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author | Daniel Vetter <daniel.vetter@ffwll.ch> | 2019-06-07 00:27:42 +0200 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-10-07 18:58:28 +0200 |
commit | b66b85d544947d4588ad7fdfe14d38f89a6d15c1 (patch) | |
tree | 4ef68e179a84579689e92f5963f02c6646474d3e /drivers/gpu/drm | |
parent | c036f925087e068659f738603d5a76d7d5848772 (diff) | |
download | linux-stable-b66b85d544947d4588ad7fdfe14d38f89a6d15c1.tar.gz linux-stable-b66b85d544947d4588ad7fdfe14d38f89a6d15c1.tar.bz2 linux-stable-b66b85d544947d4588ad7fdfe14d38f89a6d15c1.zip |
drm/vkms: Fix crc worker races
[ Upstream commit 18d0952a838ba559655b0cd9cf85097ad63d9bca ]
The issue we have is that the crc worker might fall behind. We've
tried to handle this by tracking both the earliest frame for which it
still needs to compute a crc, and the last one. Plus when the
crtc_state changes, we have a new work item, which are all run in
order due to the ordered workqueue we allocate for each vkms crtc.
Trouble is there's been a few small issues in the current code:
- we need to capture frame_end in the vblank hrtimer, not in the
worker. The worker might run much later, and then we generate a lot
of crc for which there's already a different worker queued up.
- frame number might be 0, so create a new crc_pending boolean to
track this without confusion.
- we need to atomically grab frame_start/end and clear it, so do that
all in one go. This is not going to create a new race, because if we
race with the hrtimer then our work will be re-run.
- only race that can happen is the following:
1. worker starts
2. hrtimer runs and updates frame_end
3. worker grabs frame_start/end, already reading the new frame_end,
and clears crc_pending
4. hrtimer calls queue_work()
5. worker completes
6. worker gets re-run, crc_pending is false
Explain this case a bit better by rewording the comment.
v2: Demote warning level output to debug when we fail to requeue, this
is expected under high load when the crc worker can't quite keep up.
Cc: Shayenne Moura <shayenneluzmoura@gmail.com>
Cc: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Cc: Haneen Mohammed <hamohammed.sa@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Tested-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190606222751.32567-2-daniel.vetter@ffwll.ch
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'drivers/gpu/drm')
-rw-r--r-- | drivers/gpu/drm/vkms/vkms_crc.c | 27 | ||||
-rw-r--r-- | drivers/gpu/drm/vkms/vkms_crtc.c | 9 | ||||
-rw-r--r-- | drivers/gpu/drm/vkms/vkms_drv.h | 2 |
3 files changed, 22 insertions, 16 deletions
diff --git a/drivers/gpu/drm/vkms/vkms_crc.c b/drivers/gpu/drm/vkms/vkms_crc.c index d7b409a3c0f8..66603da634fe 100644 --- a/drivers/gpu/drm/vkms/vkms_crc.c +++ b/drivers/gpu/drm/vkms/vkms_crc.c @@ -166,16 +166,24 @@ void vkms_crc_work_handle(struct work_struct *work) struct drm_plane *plane; u32 crc32 = 0; u64 frame_start, frame_end; + bool crc_pending; unsigned long flags; spin_lock_irqsave(&out->state_lock, flags); frame_start = crtc_state->frame_start; frame_end = crtc_state->frame_end; + crc_pending = crtc_state->crc_pending; + crtc_state->frame_start = 0; + crtc_state->frame_end = 0; + crtc_state->crc_pending = false; spin_unlock_irqrestore(&out->state_lock, flags); - /* _vblank_handle() hasn't updated frame_start yet */ - if (!frame_start || frame_start == frame_end) - goto out; + /* + * We raced with the vblank hrtimer and previous work already computed + * the crc, nothing to do. + */ + if (!crc_pending) + return; drm_for_each_plane(plane, &vdev->drm) { struct vkms_plane_state *vplane_state; @@ -196,20 +204,11 @@ void vkms_crc_work_handle(struct work_struct *work) if (primary_crc) crc32 = _vkms_get_crc(primary_crc, cursor_crc); - frame_end = drm_crtc_accurate_vblank_count(crtc); - - /* queue_work can fail to schedule crc_work; add crc for - * missing frames + /* + * The worker can fall behind the vblank hrtimer, make sure we catch up. */ while (frame_start <= frame_end) drm_crtc_add_crc_entry(crtc, true, frame_start++, &crc32); - -out: - /* to avoid using the same value for frame number again */ - spin_lock_irqsave(&out->state_lock, flags); - crtc_state->frame_end = frame_end; - crtc_state->frame_start = 0; - spin_unlock_irqrestore(&out->state_lock, flags); } static int vkms_crc_parse_source(const char *src_name, bool *enabled) diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c b/drivers/gpu/drm/vkms/vkms_crtc.c index e447b7588d06..77a1f5fa5d5c 100644 --- a/drivers/gpu/drm/vkms/vkms_crtc.c +++ b/drivers/gpu/drm/vkms/vkms_crtc.c @@ -30,13 +30,18 @@ static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer) * has read the data */ spin_lock(&output->state_lock); - if (!state->frame_start) + if (!state->crc_pending) state->frame_start = frame; + else + DRM_DEBUG_DRIVER("crc worker falling behind, frame_start: %llu, frame_end: %llu\n", + state->frame_start, frame); + state->frame_end = frame; + state->crc_pending = true; spin_unlock(&output->state_lock); ret = queue_work(output->crc_workq, &state->crc_work); if (!ret) - DRM_WARN("failed to queue vkms_crc_work_handle"); + DRM_DEBUG_DRIVER("vkms_crc_work_handle already queued\n"); } spin_unlock(&output->lock); diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h index 81f1cfbeb936..3c7e06b19efd 100644 --- a/drivers/gpu/drm/vkms/vkms_drv.h +++ b/drivers/gpu/drm/vkms/vkms_drv.h @@ -56,6 +56,8 @@ struct vkms_plane_state { struct vkms_crtc_state { struct drm_crtc_state base; struct work_struct crc_work; + + bool crc_pending; u64 frame_start; u64 frame_end; }; |