Messages in this thread | | | Subject | Re: [PATCH 1/3] drm: use the lookup lock in drm_is_current_master | From | Desmond Cheong Zhi Xi <> | Date | Thu, 29 Jul 2021 22:32:13 +0800 |
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On 29/7/21 3:00 pm, Daniel Vetter wrote: > On Tue, Jul 27, 2021 at 04:37:22PM +0200, Peter Zijlstra wrote: >> On Thu, Jul 22, 2021 at 12:38:10PM +0200, Daniel Vetter wrote: >>> On Thu, Jul 22, 2021 at 05:29:27PM +0800, Desmond Cheong Zhi Xi wrote: >>>> Inside drm_is_current_master, using the outer drm_device.master_mutex >>>> to protect reads of drm_file.master makes the function prone to creating >>>> lock hierarchy inversions. Instead, we can use the >>>> drm_file.master_lookup_lock that sits at the bottom of the lock >>>> hierarchy. >>>> >>>> Reported-by: Daniel Vetter <daniel.vetter@ffwll.ch> >>>> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> >>>> --- >>>> drivers/gpu/drm/drm_auth.c | 9 +++++---- >>>> 1 file changed, 5 insertions(+), 4 deletions(-) >>>> >>>> diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c >>>> index f00354bec3fb..9c24b8cc8e36 100644 >>>> --- a/drivers/gpu/drm/drm_auth.c >>>> +++ b/drivers/gpu/drm/drm_auth.c >>>> @@ -63,8 +63,9 @@ >>>> >>>> static bool drm_is_current_master_locked(struct drm_file *fpriv) >>>> { >>>> - lockdep_assert_held_once(&fpriv->minor->dev->master_mutex); >>>> - >>>> + /* Either drm_device.master_mutex or drm_file.master_lookup_lock >>>> + * should be held here. >>>> + */ >>> >>> Disappointing that lockdep can't check or conditions for us, a >>> lockdep_assert_held_either would be really neat in some cases. >>> >>> Adding lockdep folks, maybe they have ideas. >> >> #ifdef CONFIG_LOCKDEP >> WARN_ON_ONCE(debug_locks && !(lockdep_is_held(&drm_device.master_mutex) || >> lockdep_is_held(&drm_file.master_lookup_lock))); >> #endif >> >> doesn't exactly roll off the tongue, but should do as you want I >> suppose. >> >> Would something like: >> >> #define lockdep_assert(cond) WARN_ON_ONCE(debug_locks && !(cond)) >> >> Such that we can write: >> >> lockdep_assert(lockdep_is_held(&drm_device.master_mutex) || >> lockdep_is_held(&drm_file.master_lookup_lock)); >> >> make it better ? > > Yeah I think that's pretty tidy and flexible. > > Desmond, can you pls give this a shot with Peter's patch below? > -Daniel
Sounds good, will do. Thanks for the patch, Peter.
Just going to make a small edit: s/LOCK_STAT_NOT_HELD/LOCK_STATE_NOT_HELD/
Best wishes, Desmond
>> >> --- >> Subject: locking/lockdep: Provide lockdep_assert{,_once}() helpers >> >> Extract lockdep_assert{,_once}() helpers to more easily write composite >> assertions like, for example: >> >> lockdep_assert(lockdep_is_held(&drm_device.master_mutex) || >> lockdep_is_held(&drm_file.master_lookup_lock)); >> >> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> >> --- >> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h >> index 5cf387813754..0da67341c1fb 100644 >> --- a/include/linux/lockdep.h >> +++ b/include/linux/lockdep.h >> @@ -306,31 +306,29 @@ extern void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie); >> >> #define lockdep_depth(tsk) (debug_locks ? (tsk)->lockdep_depth : 0) >> >> -#define lockdep_assert_held(l) do { \ >> - WARN_ON(debug_locks && \ >> - lockdep_is_held(l) == LOCK_STATE_NOT_HELD); \ >> - } while (0) >> +#define lockdep_assert(cond) \ >> + do { WARN_ON(debug_locks && !(cond)); } while (0) >> >> -#define lockdep_assert_not_held(l) do { \ >> - WARN_ON(debug_locks && \ >> - lockdep_is_held(l) == LOCK_STATE_HELD); \ >> - } while (0) >> +#define lockdep_assert_once(cond) \ >> + do { WARN_ON_ONCE(debug_locks && !(cond)); } while (0) >> >> -#define lockdep_assert_held_write(l) do { \ >> - WARN_ON(debug_locks && !lockdep_is_held_type(l, 0)); \ >> - } while (0) >> +#define lockdep_assert_held(l) \ >> + lockdep_assert(lockdep_is_held(l) != LOCK_STAT_NOT_HELD) >> >> -#define lockdep_assert_held_read(l) do { \ >> - WARN_ON(debug_locks && !lockdep_is_held_type(l, 1)); \ >> - } while (0) >> +#define lockdep_assert_not_held(l) \ >> + lockdep_assert(lockdep_is_held(l) != LOCK_STATE_HELD) >> >> -#define lockdep_assert_held_once(l) do { \ >> - WARN_ON_ONCE(debug_locks && !lockdep_is_held(l)); \ >> - } while (0) >> +#define lockdep_assert_held_write(l) \ >> + lockdep_assert(lockdep_is_held_type(l, 0)) >> >> -#define lockdep_assert_none_held_once() do { \ >> - WARN_ON_ONCE(debug_locks && current->lockdep_depth); \ >> - } while (0) >> +#define lockdep_assert_held_read(l) \ >> + lockdep_assert(lockdep_is_held_type(l, 1)) >> + >> +#define lockdep_assert_held_once(l) \ >> + lockdep_assert_once(lockdep_is_held(l) != LOCK_STAT_NOT_HELD) >> + >> +#define lockdep_assert_none_held_once() \ >> + lockdep_assert_once(!current->lockdep_depth) >> >> #define lockdep_recursing(tsk) ((tsk)->lockdep_recursion) >> >> @@ -407,6 +405,9 @@ extern int lock_is_held(const void *); >> extern int lockdep_is_held(const void *); >> #define lockdep_is_held_type(l, r) (1) >> >> +#define lockdep_assert(c) do { } while (0) >> +#define lockdep_assert_once(c) do { } while (0) >> + >> #define lockdep_assert_held(l) do { (void)(l); } while (0) >> #define lockdep_assert_not_held(l) do { (void)(l); } while (0) >> #define lockdep_assert_held_write(l) do { (void)(l); } while (0) >> >
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