diff options
| author | Maíra Canal <mcanal@igalia.com> | 2024-04-20 18:32:13 -0300 |
|---|---|---|
| committer | Maíra Canal <mcanal@igalia.com> | 2024-04-23 19:32:49 -0300 |
| commit | 6abe93b621ab12e93cf0eb7e42a609b36be32da1 (patch) | |
| tree | 2dcd038c91e82421c87eec1da93e3a2149f18d5f /drivers/gpu/drm/v3d/v3d_drv.c | |
| parent | 12d1624ce3d3fb030180384f9725d059538e5605 (diff) | |
drm/v3d: Fix race-condition between sysfs/fdinfo and interrupt handler
In V3D, the conclusion of a job is indicated by a IRQ. When a job
finishes, then we update the local and the global GPU stats of that
queue. But, while the GPU stats are being updated, a user might be
reading the stats from sysfs or fdinfo.
For example, on `gpu_stats_show()`, we could think about a scenario where
`v3d->queue[queue].start_ns != 0`, then an interrupt happens, we update
the value of `v3d->queue[queue].start_ns` to 0, we come back to
`gpu_stats_show()` to calculate `active_runtime` and now,
`active_runtime = timestamp`.
In this simple example, the user would see a spike in the queue usage,
that didn't match reality.
In order to address this issue properly, use a seqcount to protect read
and write sections of the code.
Fixes: 09a93cc4f7d1 ("drm/v3d: Implement show_fdinfo() callback for GPU usage stats")
Reported-by: Tvrtko Ursulin <tursulin@igalia.com>
Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240420213632.339941-7-mcanal@igalia.com
Diffstat (limited to 'drivers/gpu/drm/v3d/v3d_drv.c')
| -rw-r--r-- | drivers/gpu/drm/v3d/v3d_drv.c | 14 |
1 files changed, 10 insertions, 4 deletions
diff --git a/drivers/gpu/drm/v3d/v3d_drv.c b/drivers/gpu/drm/v3d/v3d_drv.c index 2ec359ed2def..28b7ddce7747 100644 --- a/drivers/gpu/drm/v3d/v3d_drv.c +++ b/drivers/gpu/drm/v3d/v3d_drv.c @@ -121,6 +121,7 @@ v3d_open(struct drm_device *dev, struct drm_file *file) 1, NULL); memset(&v3d_priv->stats[i], 0, sizeof(v3d_priv->stats[i])); + seqcount_init(&v3d_priv->stats[i].lock); } v3d_perfmon_open_file(v3d_priv); @@ -145,10 +146,15 @@ v3d_postclose(struct drm_device *dev, struct drm_file *file) void v3d_get_stats(const struct v3d_stats *stats, u64 timestamp, u64 *active_runtime, u64 *jobs_completed) { - *active_runtime = stats->enabled_ns; - if (stats->start_ns) - *active_runtime += timestamp - stats->start_ns; - *jobs_completed = stats->jobs_completed; + unsigned int seq; + + do { + seq = read_seqcount_begin(&stats->lock); + *active_runtime = stats->enabled_ns; + if (stats->start_ns) + *active_runtime += timestamp - stats->start_ns; + *jobs_completed = stats->jobs_completed; + } while (read_seqcount_retry(&stats->lock, seq)); } static void v3d_show_fdinfo(struct drm_printer *p, struct drm_file *file) |