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Message-ID: <7ee0205a-6522-465b-8795-3d7b867e2d97@ursulin.net>
Date: Tue, 11 Feb 2025 11:39:49 +0000
From: Tvrtko Ursulin <tursulin@...ulin.net>
To: Adrián Larumbe <adrian.larumbe@...labora.com>
Cc: Boris Brezillon <boris.brezillon@...labora.com>,
Steven Price <steven.price@....com>, Liviu Dudau <liviu.dudau@....com>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
kernel@...labora.com, dri-devel@...ts.freedesktop.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] drm/panthor: Replace sleep locks with spinlocks in
fdinfo path
On 10/02/2025 16:08, Adrián Larumbe wrote:
> Hi Tvrtko,
Thanks!
> [18153.770244] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:562
> [18153.771059] in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 203412, name: cat
> [18153.771757] preempt_count: 1, expected: 0
> [18153.772164] RCU nest depth: 0, expected: 0
> [18153.772538] INFO: lockdep is turned off.
> [18153.772898] CPU: 4 UID: 0 PID: 203412 Comm: cat Tainted: G W 6.14.0-rc1-panthor-next-rk3588-fdinfo+ #1
> [18153.772906] Tainted: [W]=WARN
> [18153.772908] Hardware name: Radxa ROCK 5B (DT)
> [18153.772911] Call trace:
> [18153.772913] show_stack+0x24/0x38 (C)
> [18153.772927] dump_stack_lvl+0x3c/0x98
> [18153.772935] dump_stack+0x18/0x24
> [18153.772941] __might_resched+0x298/0x2b0
> [18153.772948] __might_sleep+0x6c/0xb0
> [18153.772953] __mutex_lock_common+0x7c/0x1950
> [18153.772962] mutex_lock_nested+0x38/0x50
> [18153.772969] panthor_fdinfo_gather_group_samples+0x80/0x138 [panthor]
> [18153.773042] panthor_show_fdinfo+0x80/0x228 [panthor]
> [18153.773109] drm_show_fdinfo+0x1a4/0x1e0 [drm]
> [18153.773397] seq_show+0x274/0x358
> [18153.773404] seq_read_iter+0x1d4/0x630
There is a mutex_lock literally in seq_read_iter.
So colour me confused. What created the atomic context between then and
Panthor code?! I just don't see it.
Regards,
Tvrtko
> [18153.773411] seq_read+0x148/0x1a0
> [18153.773416] vfs_read+0x114/0x3e0
> [18153.773423] ksys_read+0x90/0x110
> [18153.773429] __arm64_sys_read+0x50/0x70
> [18153.773435] invoke_syscall+0x60/0x178
> [18153.773442] el0_svc_common+0x104/0x148
> [18153.773447] do_el0_svc+0x3c/0x58
> [18153.773453] el0_svc+0x50/0xa8
> [18153.773459] el0t_64_sync_handler+0x78/0x108
> [18153.773465] el0t_64_sync+0x198/0x1a0
>
>
> On 10.02.2025 15:52, Tvrtko Ursulin wrote:
>> 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 <adrian.larumbe@...labora.com>
>>> 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 <drm/panthor_drm.h>
>>> #include <linux/build_bug.h>
>>> +#include <linux/cleanup.h>
>>> #include <linux/clk.h>
>>> #include <linux/delay.h>
>>> #include <linux/dma-mapping.h>
>>> @@ -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
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