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Mon, 10 Feb 2025 07:52:36 -0800 (PST) Message-ID: <2ec2a848-90f4-49bc-aaaf-8eb256f271db@ursulin.net> Date: Mon, 10 Feb 2025 15:52:35 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] drm/panthor: Replace sleep locks with spinlocks in fdinfo path To: =?UTF-8?Q?Adri=C3=A1n_Larumbe?= , Boris Brezillon , Steven Price , Liviu Dudau , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter Cc: kernel@collabora.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org References: <20250210124203.124191-1-adrian.larumbe@collabora.com> Content-Language: en-GB From: Tvrtko Ursulin In-Reply-To: <20250210124203.124191-1-adrian.larumbe@collabora.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 10/02/2025 12:41, Adrián Larumbe wrote: > Panthor's fdinfo handler is routed through the /proc file system, which > executes in an atomic context. That means we cannot use mutexes because > they might sleep. Have the debug splat at hand? I am thinking it is not because of fdinfo reads, which are allowed to sleep, but has to be something else. Regards, Tvrtko > This bug was uncovered by enabling some of the kernel's mutex-debugging > features: > > CONFIG_DEBUG_RT_MUTEXES=y > CONFIG_DEBUG_MUTEXES=y > > Replace Panthor's group fdinfo data mutex with a guarded spinlock. > > Signed-off-by: Adrián Larumbe > Fixes: e16635d88fa0 ("drm/panthor: add DRM fdinfo support") > --- > drivers/gpu/drm/panthor/panthor_sched.c | 26 ++++++++++++------------- > 1 file changed, 12 insertions(+), 14 deletions(-) > > diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c > index 0b93bf83a9b2..7a267d1efeb6 100644 > --- a/drivers/gpu/drm/panthor/panthor_sched.c > +++ b/drivers/gpu/drm/panthor/panthor_sched.c > @@ -9,6 +9,7 @@ > #include > > #include > +#include > #include > #include > #include > @@ -631,10 +632,10 @@ struct panthor_group { > struct panthor_gpu_usage data; > > /** > - * @lock: Mutex to govern concurrent access from drm file's fdinfo callback > - * and job post-completion processing function > + * @fdinfo.lock: Spinlock to govern concurrent access from drm file's fdinfo > + * callback and job post-completion processing function > */ > - struct mutex lock; > + spinlock_t lock; > > /** @fdinfo.kbo_sizes: Aggregate size of private kernel BO's held by the group. */ > size_t kbo_sizes; > @@ -910,8 +911,6 @@ static void group_release_work(struct work_struct *work) > release_work); > u32 i; > > - mutex_destroy(&group->fdinfo.lock); > - > for (i = 0; i < group->queue_count; i++) > group_free_queue(group, group->queues[i]); > > @@ -2861,12 +2860,12 @@ static void update_fdinfo_stats(struct panthor_job *job) > struct panthor_job_profiling_data *slots = queue->profiling.slots->kmap; > struct panthor_job_profiling_data *data = &slots[job->profiling.slot]; > > - mutex_lock(&group->fdinfo.lock); > - if (job->profiling.mask & PANTHOR_DEVICE_PROFILING_CYCLES) > - fdinfo->cycles += data->cycles.after - data->cycles.before; > - if (job->profiling.mask & PANTHOR_DEVICE_PROFILING_TIMESTAMP) > - fdinfo->time += data->time.after - data->time.before; > - mutex_unlock(&group->fdinfo.lock); > + scoped_guard(spinlock, &group->fdinfo.lock) { > + if (job->profiling.mask & PANTHOR_DEVICE_PROFILING_CYCLES) > + fdinfo->cycles += data->cycles.after - data->cycles.before; > + if (job->profiling.mask & PANTHOR_DEVICE_PROFILING_TIMESTAMP) > + fdinfo->time += data->time.after - data->time.before; > + } > } > > void panthor_fdinfo_gather_group_samples(struct panthor_file *pfile) > @@ -2880,12 +2879,11 @@ void panthor_fdinfo_gather_group_samples(struct panthor_file *pfile) > > xa_lock(&gpool->xa); > xa_for_each(&gpool->xa, i, group) { > - mutex_lock(&group->fdinfo.lock); > + guard(spinlock)(&group->fdinfo.lock); > pfile->stats.cycles += group->fdinfo.data.cycles; > pfile->stats.time += group->fdinfo.data.time; > group->fdinfo.data.cycles = 0; > group->fdinfo.data.time = 0; > - mutex_unlock(&group->fdinfo.lock); > } > xa_unlock(&gpool->xa); > } > @@ -3531,7 +3529,7 @@ int panthor_group_create(struct panthor_file *pfile, > mutex_unlock(&sched->reset.lock); > > add_group_kbo_sizes(group->ptdev, group); > - mutex_init(&group->fdinfo.lock); > + spin_lock_init(&group->fdinfo.lock); > > return gid; > > > base-commit: 2eca617f12586abff62038db1c14cb3aa60a15aa > prerequisite-patch-id: 7e787ce5973b5fc7e9f69f26aa4d7e5ec03d5caa > prerequisite-patch-id: 03a619b8c741444b28435850e23d9ec463171c13 > prerequisite-patch-id: 290e1053f8bf4a8b80fb037a87cae7e096b5aa96 > prerequisite-patch-id: bc49bb8c29905650fb4788acc528bb44013c0240 > prerequisite-patch-id: 46cab4c980824c03e5164afc43085fec23e1cba5