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    Subject[PATCH AUTOSEL for 4.14 34/67] media: s5p-mfc: Fix lock contention - request_firmware() once
    Date
    From: Shuah Khan <shuahkh@osg.samsung.com>

    [ Upstream commit f45ce9877561044090010e0eb0fad644232ded04 ]

    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 ***

    Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
    Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
    Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    ---
    drivers/media/platform/s5p-mfc/s5p_mfc.c | 6 ++++++
    drivers/media/platform/s5p-mfc/s5p_mfc_common.h | 3 +++
    drivers/media/platform/s5p-mfc/s5p_mfc_ctrl.c | 5 +++++
    3 files changed, 14 insertions(+)

    diff --git a/drivers/media/platform/s5p-mfc/s5p_mfc.c b/drivers/media/platform/s5p-mfc/s5p_mfc.c
    index 1afde5021ca6..8e9531f7f83f 100644
    --- a/drivers/media/platform/s5p-mfc/s5p_mfc.c
    +++ b/drivers/media/platform/s5p-mfc/s5p_mfc.c
    @@ -1315,6 +1315,12 @@ static int s5p_mfc_probe(struct platform_device *pdev)
    goto err_dma;
    }

    + /*
    + * Load fails if fs isn't mounted. Try loading anyway.
    + * _open() will load it, it it fails now. Ignore failure.
    + */
    + s5p_mfc_load_firmware(dev);
    +
    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 4220914529b2..76119a8cc477 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 69ef9c23a99a..d94e59e79fe9 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;
    +
    for (i = MFC_FW_MAX_VERSIONS - 1; i >= 0; i--) {
    if (!dev->variant->fw_name[i])
    continue;
    @@ -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;
    }

    --
    2.14.1
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