On Mon, 18 May 2026 11:16:55 +0200 Christian König <[email protected]> wrote:
> On 5/18/26 10:28, Boris Brezillon wrote: > > On Thu, 14 May 2026 11:34:52 -0700 > > Chia-I Wu <[email protected]> wrote: > > > >> On Wed, May 13, 2026 at 10:24 AM Boris Brezillon > >> <[email protected]> wrote: > >>> > >>> Define a conditional drm_dev_access guard to automate the > >>> drm_dev_{enter,exit}() sequence. > >>> > >>> Signed-off-by: Boris Brezillon <[email protected]> > >>> --- > >>> include/drm/drm_drv.h | 9 +++++++++ > >>> 1 file changed, 9 insertions(+) > >>> > >>> diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h > >>> index 42fc085f986d..79d1958f93e4 100644 > >>> --- a/include/drm/drm_drv.h > >>> +++ b/include/drm/drm_drv.h > >>> @@ -490,6 +490,15 @@ void drm_dev_unplug(struct drm_device *dev); > >>> int drm_dev_wedged_event(struct drm_device *dev, unsigned long method, > >>> struct drm_wedge_task_info *info); > >>> > >>> +/* > >>> + * Only the conditional drm_dev_access guard is valid. The drm_dev one is > >>> + * here so we can extend it with a conditional variant. > >>> + */ > >>> +DEFINE_LOCK_GUARD_1(drm_dev, struct drm_device, > >>> + { WARN_ON("Use cond guards"); _T->idx = -1; }, > >>> + drm_dev_exit(_T->idx), int idx); > >> If this is ever mis-used, drm_dev_exit(-1) seems to cause OOB access. > >> Is BUG more appropriate than WARN_ON? > > > > I actually had > > > > if (_T->idx >= 0) drm_dev_exit(_T->idx), > > > > at some point, and I ditched it thinking the WARN_ON_ONCE() > > in srcu_read_unlock() would cover for that. I can add it back, of > > course. > > > > I'd be fine with a BUG_ON() too, but every time I tried to add one I've > > been encouraged to handle the unexpected case instead. > > > > Ideally, we would have a DEFINE_LOCK_GUARD_COND() variant that, instead > > of expanding a non-conditional one, would define the whole thing so > > that the non-conditional variant is never exposed. > > Would it be possible to use BUILD_BUG() here? Ah, nice! I was searching for this kind of compile-time assert that would trigger if the code is used, and BUILD_BUG() indeed does what we want. Thanks for the tip.
