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Subject[PATCH 2/2] media: s5p-mfc: fix lock confection - request_firmware() once and keep state
Date
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 | 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");
+
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;
}

--
2.7.4
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