Re: [PATCH v2 07/22] drm/msm: Do rpm get sooner in the submit path

From: Rob Clark
Date: Mon Oct 12 2020 - 11:44:05 EST

On Mon, Oct 12, 2020 at 7:35 AM Daniel Vetter <daniel@xxxxxxxx> wrote:
>
> On Sun, Oct 11, 2020 at 07:09:34PM -0700, Rob Clark wrote:
> > From: Rob Clark <robdclark@xxxxxxxxxxxx>
> >
> > Unfortunately, due to an dev_pm_opp locking interaction with
> > mm->mmap_sem, we need to do pm get before aquiring obj locks,
> > otherwise we can have anger lockdep with the chain:
>
> tbh this sounds like a bug in that subsystem, since it means we cannot use
> said subsystem in mmap handlers either.
>
> So if you have some remapping unit or need to wake up your gpu to blt the
> buffer into system memory first, we're toast. That doesn't sound right. So
> maybe Cc: pm folks and figure out how to fix this long term properly? Imo
> not a good reason to hold up this patch set, since unwrangling mmap_sem
> tends to be work ...

+ a couple of PM folks

Looks like it has been this way for quite some time, so I guess the
overlap between things using dev_pm_opp and mmap is low..

fwiw, example splat so folks can see the locking interaction I am
talking about.. I suspect the pm_opp interaction with mm->mmap_sem is
from the debugfs calls while opp_table_lock is held?

[ 15.627855] ======================================================
[ 15.634202] WARNING: possible circular locking dependency detected
[ 15.640550] 5.4.70 #41 Not tainted
[ 15.644050] ------------------------------------------------------
[ 15.650397] chrome/1805 is trying to acquire lock:
[ 15.655314] ffffffed90720738 (opp_table_lock){+.+.}, at:
_find_opp_table+0x34/0x74
[ 15.663092]
[ 15.663092] but task is already holding lock:
[ 15.669082] ffffff80ff3911a8 (reservation_ww_class_mutex){+.+.},
at: submit_lock_objects+0x70/0x1ec
[ 15.678369]
[ 15.678369] which lock already depends on the new lock.
[ 15.678369]
[ 15.686764]
[ 15.686764] the existing dependency chain (in reverse order) is:
[ 15.694438]
[ 15.694438] -> #3 (reservation_ww_class_mutex){+.+.}:
[ 15.701146] __mutex_lock_common+0xec/0xc0c
[ 15.705978] ww_mutex_lock_interruptible+0x5c/0xc4
[ 15.711432] msm_gem_fault+0x2c/0x124
[ 15.715731] __do_fault+0x40/0x16c
[ 15.719766] handle_mm_fault+0x7cc/0xd98
[ 15.724337] do_page_fault+0x230/0x3b4
[ 15.728721] do_translation_fault+0x5c/0x78
[ 15.733558] do_mem_abort+0x4c/0xb4
[ 15.737680] el0_da+0x1c/0x20
[ 15.741266]
[ 15.741266] -> #2 (&mm->mmap_sem){++++}:
[ 15.746809] __might_fault+0x70/0x98
[ 15.751022] compat_filldir+0xf8/0x48c
[ 15.755412] dcache_readdir+0x70/0x1dc
[ 15.759808] iterate_dir+0xd4/0x180
[ 15.763931] __arm64_compat_sys_getdents+0xa0/0x19c
[ 15.769476] el0_svc_common+0xa8/0x178
[ 15.773861] el0_svc_compat_handler+0x2c/0x40
[ 15.778868] el0_svc_compat+0x8/0x10
[ 15.783075]
[ 15.783075] -> #1 (&sb->s_type->i_mutex_key#3){++++}:
[ 15.789788] down_write+0x54/0x16c
[ 15.793826] debugfs_remove_recursive+0x50/0x158
[ 15.799108] opp_debug_unregister+0x34/0x114
[ 15.804028] dev_pm_opp_put_opp_table+0xd0/0x14c
[ 15.809308] dev_pm_opp_put_clkname+0x3c/0x50
[ 15.814318] msm_dsi_host_destroy+0xb0/0xcc
[ 15.819149] dsi_destroy+0x40/0x58
[ 15.823184] dsi_bind+0x90/0x170
[ 15.827041] component_bind_all+0xf0/0x208
[ 15.831787] msm_drm_init+0x188/0x60c
[ 15.836084] msm_drm_bind+0x24/0x30
[ 15.840205] try_to_bring_up_master+0x15c/0x1a4
[ 15.845396] __component_add+0x98/0x14c
[ 15.849878] component_add+0x28/0x34
[ 15.854086] dp_display_probe+0x324/0x370
[ 15.858744] platform_drv_probe+0x90/0xb0
[ 15.863400] really_probe+0x134/0x2ec
[ 15.867699] driver_probe_device+0x64/0xfc
[ 15.872443] __device_attach_driver+0x8c/0xa4
[ 15.877459] bus_for_each_drv+0x90/0xd8
[ 15.881939] __device_attach+0xc0/0x148
[ 15.886420] device_initial_probe+0x20/0x2c
[ 15.891254] bus_probe_device+0x34/0x94
[ 15.895726] deferred_probe_work_func+0x78/0xb4
[ 15.900914] process_one_work+0x30c/0x5d0
[ 15.905573] worker_thread+0x240/0x3f0
[ 15.909959] kthread+0x144/0x154
[ 15.913809] ret_from_fork+0x10/0x18
[ 15.918016]
[ 15.918016] -> #0 (opp_table_lock){+.+.}:
[ 15.923660] __lock_acquire+0xee4/0x2450
[ 15.928230] lock_acquire+0x1cc/0x210
[ 15.932527] __mutex_lock_common+0xec/0xc0c
[ 15.937359] mutex_lock_nested+0x40/0x50
[ 15.941928] _find_opp_table+0x34/0x74
[ 15.946312] dev_pm_opp_find_freq_exact+0x2c/0xdc
[ 15.951680] a6xx_gmu_resume+0xc8/0xecc
[ 15.952812] fscrypt: AES-256-CTS-CBC using implementation "cts-cbc-aes-ce"
[ 15.956161] a6xx_pm_resume+0x148/0x200
[ 15.956166] adreno_resume+0x28/0x34
[ 15.956171] pm_generic_runtime_resume+0x34/0x48
[ 15.956174] __rpm_callback+0x70/0x10c
[ 15.956176] rpm_callback+0x34/0x8c
[ 15.956179] rpm_resume+0x414/0x550
[ 15.956182] __pm_runtime_resume+0x7c/0xa0
[ 15.956185] msm_gpu_submit+0x60/0x1c0
[ 15.956190] msm_ioctl_gem_submit+0xadc/0xb60
[ 16.003961] drm_ioctl_kernel+0x9c/0x118
[ 16.008532] drm_ioctl+0x27c/0x408
[ 16.012562] drm_compat_ioctl+0xcc/0xdc
[ 16.017038] __se_compat_sys_ioctl+0x100/0x206c
[ 16.022224] __arm64_compat_sys_ioctl+0x20/0x2c
[ 16.027412] el0_svc_common+0xa8/0x178
[ 16.031800] el0_svc_compat_handler+0x2c/0x40
[ 16.036810] el0_svc_compat+0x8/0x10
[ 16.041021]
[ 16.041021] other info that might help us debug this:
[ 16.041021]
[ 16.049235] Chain exists of:
[ 16.049235] opp_table_lock --> &mm->mmap_sem --> reservation_ww_class_mutex
[ 16.049235]
[ 16.061014] Possible unsafe locking scenario:
[ 16.061014]
[ 16.067091] CPU0 CPU1
[ 16.071750] ---- ----
[ 16.076399] lock(reservation_ww_class_mutex);
[ 16.081059] lock(&mm->mmap_sem);
[ 16.087134] lock(reservation_ww_class_mutex);
[ 16.094369] lock(opp_table_lock);
[ 16.097961]
[ 16.097961] *** DEADLOCK ***
[ 16.097961]
[ 16.104038] 3 locks held by chrome/1805:
[ 16.108068] #0: ffffff80fb20c0d8 (&dev->struct_mutex){+.+.}, at:
msm_ioctl_gem_submit+0x264/0xb60
[ 16.117264] #1: ffffff80dd712c70
(reservation_ww_class_acquire){+.+.}, at:
msm_ioctl_gem_submit+0x8e8/0xb60
[ 16.127357] #2: ffffff80ff3911a8
(reservation_ww_class_mutex){+.+.}, at: submit_lock_objects+0x70/0x1ec
[ 16.137089]
[ 16.137089] stack backtrace:
[ 16.141567] CPU: 4 PID: 1805 Comm: chrome Not tainted 5.4.70 #41
[ 16.147733] Hardware name: Google Lazor (rev1+) with LTE (DT)
[ 16.153632] Call trace:
[ 16.156154] dump_backtrace+0x0/0x158
[ 16.159924] show_stack+0x20/0x2c
[ 16.163340] dump_stack+0xc8/0x160
[ 16.166840] print_circular_bug+0x2c4/0x2c8
[ 16.171144] check_noncircular+0x1a8/0x1b0
[ 16.175351] __lock_acquire+0xee4/0x2450
[ 16.179382] lock_acquire+0x1cc/0x210
[ 16.183146] __mutex_lock_common+0xec/0xc0c
[ 16.187450] mutex_lock_nested+0x40/0x50
[ 16.191481] _find_opp_table+0x34/0x74
[ 16.195344] dev_pm_opp_find_freq_exact+0x2c/0xdc
[ 16.200178] a6xx_gmu_resume+0xc8/0xecc
[ 16.204120] a6xx_pm_resume+0x148/0x200
[ 16.208064] adreno_resume+0x28/0x34
[ 16.211743] pm_generic_runtime_resume+0x34/0x48
[ 16.216488] __rpm_callback+0x70/0x10c
[ 16.220342] rpm_callback+0x34/0x8c
[ 16.223933] rpm_resume+0x414/0x550
[ 16.227524] __pm_runtime_resume+0x7c/0xa0
[ 16.231731] msm_gpu_submit+0x60/0x1c0
[ 16.235586] msm_ioctl_gem_submit+0xadc/0xb60
[ 16.240066] drm_ioctl_kernel+0x9c/0x118
[ 16.244097] drm_ioctl+0x27c/0x408
[ 16.247602] drm_compat_ioctl+0xcc/0xdc
[ 16.251546] __se_compat_sys_ioctl+0x100/0x206c
[ 16.256204] __arm64_compat_sys_ioctl+0x20/0x2c
[ 16.260861] el0_svc_common+0xa8/0x178
[ 16.264716] el0_svc_compat_handler+0x2c/0x40
[ 16.269196] el0_svc_compat+0x8/0x10

BR,
-R

> -Daniel
>
> >
> > opp_table_lock --> &mm->mmap_sem --> reservation_ww_class_mutex
> >
> > For an explicit fencing userspace, the impact should be minimal
> > as we do all the fence waits before this point. It could result
> > in some needless resumes in error cases, etc.
> >
> > Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx>
> > ---
> > drivers/gpu/drm/msm/msm_gem_submit.c | 15 +++++++++++++--
> > 1 file changed, 13 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c
> > index 002130d826aa..a9422d043bfe 100644
> > --- a/drivers/gpu/drm/msm/msm_gem_submit.c
> > +++ b/drivers/gpu/drm/msm/msm_gem_submit.c
> > @@ -744,11 +744,20 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
> >
> > ret = submit_lookup_objects(submit, args, file);
> > if (ret)
> > - goto out;
> > + goto out_pre_pm;
> >
> > ret = submit_lookup_cmds(submit, args, file);
> > if (ret)
> > - goto out;
> > + goto out_pre_pm;
> > +
> > + /*
> > + * Thanks to dev_pm_opp opp_table_lock interactions with mm->mmap_sem
> > + * in the resume path, we need to to rpm get before we lock objs.
> > + * Which unfortunately might involve powering up the GPU sooner than
> > + * is necessary. But at least in the explicit fencing case, we will
> > + * have already done all the fence waiting.
> > + */
> > + pm_runtime_get_sync(&gpu->pdev->dev);
> >
> > /* copy_*_user while holding a ww ticket upsets lockdep */
> > ww_acquire_init(&submit->ticket, &reservation_ww_class);
> > @@ -825,6 +834,8 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
> >
> >
> > out:
> > + pm_runtime_put(&gpu->pdev->dev);
> > +out_pre_pm:
> > submit_cleanup(submit);
> > if (has_ww_ticket)
> > ww_acquire_fini(&submit->ticket);
> > --
> > 2.26.2
> >
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch