[PATCH v2 0/2] Fix s5p-mfc lock contention in request firmware paths

[PATCH v2 0/2] Fix s5p-mfc lock contention in request firmware paths

[Shuah Khan]

This patch series fixes inefficiencies and lock contention in the request
firmware paths.

Changes since v2:
- Addressed Andre's review comments. Removed fw_buf->virt null check
  as it is not needed. Removed handling s5p_mfc_load_firmware() from
  probe routine. Simply try loading in case it works.

Shuah Khan (2):
  media: s5p-mfc: remove firmware buf null check in
    s5p_mfc_load_firmware()
  media: s5p-mfc: fix lock confection - request_firmware() once and keep
    state

 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   | 10 +++++-----
 3 files changed, 14 insertions(+), 5 deletions(-)

-- 
2.7.4

[PATCH v2 1/2] media: s5p-mfc: remove firmware buf null check in s5p_mfc_load_firmware()

[Shuah Khan]

s5p_mfc_load_firmware() will not get called if fw_buf.virt allocation
fails. The allocation happens very early on in the probe routine and
probe fails if allocation fails.

There is no need to check if it is null in s5p_mfc_load_firmware().
Remove the check.

Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
---
 drivers/media/platform/s5p-mfc/s5p_mfc_ctrl.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/drivers/media/platform/s5p-mfc/s5p_mfc_ctrl.c b/drivers/media/platform/s5p-mfc/s5p_mfc_ctrl.c
index 69ef9c2..46c9d67 100644
--- a/drivers/media/platform/s5p-mfc/s5p_mfc_ctrl.c
+++ b/drivers/media/platform/s5p-mfc/s5p_mfc_ctrl.c
@@ -75,11 +75,6 @@ int s5p_mfc_load_firmware(struct s5p_mfc_dev *dev)
 		release_firmware(fw_blob);
 		return -ENOMEM;
 	}
-	if (!dev->fw_buf.virt) {
-		mfc_err("MFC firmware is not allocated\n");
-		release_firmware(fw_blob);
-		return -EINVAL;
-	}
 	memcpy(dev->fw_buf.virt, fw_blob->data, fw_blob->size);
 	wmb();
 	release_firmware(fw_blob);
-- 
2.7.4

[PATCH v2 2/2] media: s5p-mfc: fix lock confection - request_firmware() once and keep state

[Shuah Khan]

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>
---
 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 5cf50b3..7b9a322 100644
--- a/drivers/media/platform/s5p-mfc/s5p_mfc.c
+++ b/drivers/media/platform/s5p-mfc/s5p_mfc.c
@@ -1311,6 +1311,12 @@ 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 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 46c9d67..f95cd76 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;
@@ -77,6 +80,7 @@ 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;
@@ -88,6 +92,7 @@ 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;
 }
 
-- 
2.7.4