[PATCH 2/2] media: s5p-mfc: fix lock confection - request_firmware() once and keep state
Andrzej Hajda
a.hajda at samsung.com
Thu Nov 2 01:31:00 PDT 2017
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 at 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;
> }
>
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