Re: [PATCH 2/2] media: s5p-mfc: fix lock confection - request_firmware() once and keep state

[Andrzej Hajda <a.hajda@samsung.com>]

On 06.10.2017 23:30, Shuah Khan wrote:
> Driver calls request_firmware() whenever the device is opened for the
> first time. As the device gets opened and closed, dev->num_inst == 1
> is true several times. This is not necessary since the firmware is saved
> in the fw_buf. s5p_mfc_load_firmware() copies the buffer returned by
> the request_firmware() to dev->fw_buf.
>
> fw_buf sticks around until it gets released from s5p_mfc_remove(), hence
> there is no need to keep requesting firmware and copying it to fw_buf.
>
> This might have been overlooked when changes are made to free fw_buf from
> the device release interface s5p_mfc_release().
>
> Fix s5p_mfc_load_firmware() to call request_firmware() once and keep state.
> Change _probe() to load firmware once fw_buf has been allocated.
>
> s5p_mfc_open() and it continues to call s5p_mfc_load_firmware() and init
> hardware which is the step where firmware is written to the device.
>
> This addresses the mfc_mutex contention due to repeated request_firmware()
> calls from open() in the following circular locking warning:
>
> [  552.194115] qtdemux0:sink/2710 is trying to acquire lock:
> [  552.199488]  (&dev->mfc_mutex){+.+.}, at: [<bf145544>] s5p_mfc_mmap+0x28/0xd4 [s5p_mfc]
> [  552.207459]
>                but task is already holding lock:
> [  552.213264]  (&mm->mmap_sem){++++}, at: [<c01df2e4>] vm_mmap_pgoff+0x44/0xb8
> [  552.220284]
>                which lock already depends on the new lock.
>
> [  552.228429]
>                the existing dependency chain (in reverse order) is:
> [  552.235881]
>                -> #2 (&mm->mmap_sem){++++}:
> [  552.241259]        __might_fault+0x80/0xb0
> [  552.245331]        filldir64+0xc0/0x2f8
> [  552.249144]        call_filldir+0xb0/0x14c
> [  552.253214]        ext4_readdir+0x768/0x90c
> [  552.257374]        iterate_dir+0x74/0x168
> [  552.261360]        SyS_getdents64+0x7c/0x1a0
> [  552.265608]        ret_fast_syscall+0x0/0x28
> [  552.269850]
>                -> #1 (&type->i_mutex_dir_key#2){++++}:
> [  552.276180]        down_read+0x48/0x90
> [  552.279904]        lookup_slow+0x74/0x178
> [  552.283889]        walk_component+0x1a4/0x2e4
> [  552.288222]        link_path_walk+0x174/0x4a0
> [  552.292555]        path_openat+0x68/0x944
> [  552.296541]        do_filp_open+0x60/0xc4
> [  552.300528]        file_open_name+0xe4/0x114
> [  552.304772]        filp_open+0x28/0x48
> [  552.308499]        kernel_read_file_from_path+0x30/0x78
> [  552.313700]        _request_firmware+0x3ec/0x78c
> [  552.318291]        request_firmware+0x3c/0x54
> [  552.322642]        s5p_mfc_load_firmware+0x54/0x150 [s5p_mfc]
> [  552.328358]        s5p_mfc_open+0x4e4/0x550 [s5p_mfc]
> [  552.333394]        v4l2_open+0xa0/0x104 [videodev]
> [  552.338137]        chrdev_open+0xa4/0x18c
> [  552.342121]        do_dentry_open+0x208/0x310
> [  552.346454]        path_openat+0x28c/0x944
> [  552.350526]        do_filp_open+0x60/0xc4
> [  552.354512]        do_sys_open+0x118/0x1c8
> [  552.358586]        ret_fast_syscall+0x0/0x28
> [  552.362830]
>                -> #0 (&dev->mfc_mutex){+.+.}:
>                -> #0 (&dev->mfc_mutex){+.+.}:
> [  552.368379]        lock_acquire+0x6c/0x88
> [  552.372364]        __mutex_lock+0x68/0xa34
> [  552.376437]        mutex_lock_interruptible_nested+0x1c/0x24
> [  552.382086]        s5p_mfc_mmap+0x28/0xd4 [s5p_mfc]
> [  552.386939]        v4l2_mmap+0x54/0x88 [videodev]
> [  552.391601]        mmap_region+0x3a8/0x638
> [  552.395673]        do_mmap+0x330/0x3a4
> [  552.399400]        vm_mmap_pgoff+0x90/0xb8
> [  552.403472]        SyS_mmap_pgoff+0x90/0xc0
> [  552.407632]        ret_fast_syscall+0x0/0x28
> [  552.411876]
>                other info that might help us debug this:
>
> [  552.419848] Chain exists of:
>                  &dev->mfc_mutex --> &type->i_mutex_dir_key#2 --> &mm->mmap_sem
>
> [  552.431200]  Possible unsafe locking scenario:
>
> [  552.437092]        CPU0                    CPU1
> [  552.441598]        ----                    ----
> [  552.446104]   lock(&mm->mmap_sem);
> [  552.449484]                                lock(&type->i_mutex_dir_key#2);
> [  552.456329]                                lock(&mm->mmap_sem);
> [  552.462222]   lock(&dev->mfc_mutex);
> [  552.465775]
>                 *** DEADLOCK ***

I am not 100% but it looks like false positive. Could you describe
scenario when it deadlocks?

>
> Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
> ---
>  drivers/media/platform/s5p-mfc/s5p_mfc.c        | 4 ++++
>  drivers/media/platform/s5p-mfc/s5p_mfc_common.h | 3 +++
>  drivers/media/platform/s5p-mfc/s5p_mfc_ctrl.c   | 5 +++++
>  3 files changed, 12 insertions(+)
>
> diff --git a/drivers/media/platform/s5p-mfc/s5p_mfc.c b/drivers/media/platform/s5p-mfc/s5p_mfc.c
> index 1afde50..4c253fb 100644
> --- a/drivers/media/platform/s5p-mfc/s5p_mfc.c
> +++ b/drivers/media/platform/s5p-mfc/s5p_mfc.c
> @@ -1315,6 +1315,10 @@ static int s5p_mfc_probe(struct platform_device *pdev)
>  		goto err_dma;
>  	}
>  
> +	ret = s5p_mfc_load_firmware(dev);
> +	if (ret)
> +		mfc_err("Failed to load FW - try loading from open()\n");
> +

What is the point of adding it? It will produce error log in case
filesystem is not yet mounted, and as I remember it was the reason to
put fw load to open callback.

Regards
Andrzej

>  	mutex_init(&dev->mfc_mutex);
>  	init_waitqueue_head(&dev->queue);
>  	dev->hw_lock = 0;
> diff --git a/drivers/media/platform/s5p-mfc/s5p_mfc_common.h b/drivers/media/platform/s5p-mfc/s5p_mfc_common.h
> index 4220914..76119a8 100644
> --- a/drivers/media/platform/s5p-mfc/s5p_mfc_common.h
> +++ b/drivers/media/platform/s5p-mfc/s5p_mfc_common.h
> @@ -290,6 +290,8 @@ struct s5p_mfc_priv_buf {
>   * @mfc_cmds:		cmd structure holding HW commands function pointers
>   * @mfc_regs:		structure holding MFC registers
>   * @fw_ver:		loaded firmware sub-version
> + * @fw_get_done		flag set when request_firmware() is complete and
> + *			copied into fw_buf
>   * risc_on:		flag indicates RISC is on or off
>   *
>   */
> @@ -336,6 +338,7 @@ struct s5p_mfc_dev {
>  	struct s5p_mfc_hw_cmds *mfc_cmds;
>  	const struct s5p_mfc_regs *mfc_regs;
>  	enum s5p_mfc_fw_ver fw_ver;
> +	bool fw_get_done;
>  	bool risc_on; /* indicates if RISC is on or off */
>  };
>  
> diff --git a/drivers/media/platform/s5p-mfc/s5p_mfc_ctrl.c b/drivers/media/platform/s5p-mfc/s5p_mfc_ctrl.c
> index f064a0d1..ca57936 100644
> --- a/drivers/media/platform/s5p-mfc/s5p_mfc_ctrl.c
> +++ b/drivers/media/platform/s5p-mfc/s5p_mfc_ctrl.c
> @@ -55,6 +55,9 @@ int s5p_mfc_load_firmware(struct s5p_mfc_dev *dev)
>  	 * into kernel. */
>  	mfc_debug_enter();
>  
> +	if (dev->fw_get_done)
> +		return 0;
> +
>  	if (!dev->fw_buf.virt) {
>  		mfc_err("MFC firmware is not allocated\n");
>  		return -EINVAL;
> @@ -82,6 +85,7 @@ int s5p_mfc_load_firmware(struct s5p_mfc_dev *dev)
>  	}
>  	memcpy(dev->fw_buf.virt, fw_blob->data, fw_blob->size);
>  	wmb();
> +	dev->fw_get_done = true;
>  	release_firmware(fw_blob);
>  	mfc_debug_leave();
>  	return 0;
> @@ -93,6 +97,7 @@ int s5p_mfc_release_firmware(struct s5p_mfc_dev *dev)
>  	/* Before calling this function one has to make sure
>  	 * that MFC is no longer processing */
>  	s5p_mfc_release_priv_buf(dev, &dev->fw_buf);
> +	dev->fw_get_done = false;
>  	return 0;
>  }
>