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Date:   Fri, 29 Oct 2021 16:59:46 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     Tadeusz Struk <tadeusz.struk@...aro.org>
Cc:     Stanimir Varbanov <stanimir.varbanov@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Amit Pundir <amit.pundir@...aro.org>,
        linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] media: venus: Synchronize probe() between venus_core
 and enc/dec

On Fri, Oct 29, 2021 at 2:48 PM Tadeusz Struk <tadeusz.struk@...aro.org> wrote:
>
> Venus video encode/decode hardware driver consists of three modules.
> The parent module venus-core, and two sub modules venus-enc and venus-dec.
> The venus-core module allocates a common structure that is used by the
> enc/dec modules, loads the firmware, and performs some common hardware
> initialization. Since the three modules are loaded one after the other,
> and their probe functions can run in parallel it is possible that
> the venc_probe and vdec_probe functions can finish before the core
> venus_probe function, which then can fail when, for example it
> fails to load the firmware. In this case the subsequent call to venc_open
> causes an Oops as it tries to dereference already uninitialized structures
> through dev->parent and the system crashes in __pm_runtime_resume() as in
> the trace below:
>
> [   26.064835][  T485] Internal error: Oops: 96000006 [#1] PREEMPT SMP
> [   26.270914][  T485] Hardware name: Thundercomm Dragonboard 845c (DT)
> [   26.285019][  T485] pc : __pm_runtime_resume+0x34/0x178
> [   26.286374][  T213] lt9611 10-003b: hdmi cable connected
> [   26.290285][  T485] lr : venc_open+0xc0/0x278 [venus_enc]
> [   26.290326][  T485] Call trace:
> [   26.290328][  T485]  __pm_runtime_resume+0x34/0x178
> [   26.290330][  T485]  venc_open+0xc0/0x278 [venus_enc]
> [   26.290335][  T485]  v4l2_open+0x184/0x294
> [   26.290340][  T485]  chrdev_open+0x468/0x5c8
> [   26.290344][  T485]  do_dentry_open+0x260/0x54c
> [   26.290349][  T485]  path_openat+0xbe8/0xd5c
> [   26.290352][  T485]  do_filp_open+0xb8/0x168
> [   26.290354][  T485]  do_sys_openat2+0xa4/0x1e8
> [   26.290357][  T485]  __arm64_compat_sys_openat+0x70/0x9c
> [   26.290359][  T485]  invoke_syscall+0x60/0x170
> [   26.290363][  T485]  el0_svc_common+0xb8/0xf8
> [   26.290365][  T485]  do_el0_svc_compat+0x20/0x30
> [   26.290367][  T485]  el0_svc_compat+0x24/0x84
> [   26.290372][  T485]  el0t_32_sync_handler+0x7c/0xbc
> [   26.290374][  T485]  el0t_32_sync+0x1b8/0x1bc
> [   26.290381][  T485] ---[ end trace 04ca7c088b4c1a9c ]---
> [   26.290383][  T485] Kernel panic - not syncing: Oops: Fatal exception
>
> This can be fixed by synchronizing the three probe functions and
> only allowing the venc_probe() and vdec_probe() to pass when venus_probe()
> returns success.
>
> Changes in v2:
> - Change locking from mutex_lock to mutex_trylock
>   in venc_probe and vdec_probe to avoid potential deadlock.
>
> Signed-off-by: Tadeusz Struk <tadeusz.struk@...aro.org>

This works for me, and avoids the deadlock I was hitting with the
earlier version of the patch!

Tested-by: John Stultz <john.stultz@...aro.org>

thanks so much!
-john

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