QtMediaplayer Qt-5.12.4 play movies physical memory leak

Yocto-4.14.78
Kernel version: 4.14.78
Qt version: 5.12.4

We are using QtMeidiaPlayer to play movies, such as avi, mp4, mkv, h264 and so.
By the way, using Qt's own test program(qmlvideo), will also have this problem.

It's about one hour after we start playing moveis, some log occurs as the following:

[ 603.278905] cma: cma_alloc: alloc failed, req-size: 338 pages, ret: -12
[ 603.285713] mxc_vpu 2040000.vpu_fsl: Physical memory allocation error!
[ 603.292248] mxc_vpu 2040000.vpu_fsl: Physical memory allocation error!
[ 603.302766] cma: cma_alloc: alloc failed, req-size: 338 pages, ret: -12
[ 603.309873] mxc_vpu 2040000.vpu_fsl: Physical memory allocation error!
[ 603.316795] mxc_vpu 2040000.vpu_fsl: Physical memory allocation error!

Our board's configuration is:

[ 0.000000] Booting Linux on physical CPU 0x0
[ 0.000000] Linux version 4.14.78 (jenkins@buildhost) (gcc version 7.3.0 (GCC)) #1 PREEMPT Thu Aug 15 09:45:28 CST 2019
[ 0.000000] CPU: ARMv7 Processor [412fc09a] revision 10 (ARMv7), cr=10c53c7d
[ 0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing instruction cache
[ 0.000000] OF: fdt: Machine model: Freescale i.MX6 DualLite SABRE Smart Device Board
[ 0.000000] Memory policy: Data cache writeback
[ 0.000000] Reserved memory: created CMA memory pool at 0x3c000000, size 320 MiB
[ 0.000000] OF: reserved mem: initialized node linux,cma, compatible id shared-dma-pool
[ 0.000000] -----------[ cut here ]-----------
[ 0.000000] WARNING: CPU: 0 PID: 0 at arch/arm/kernel/devtree.c:157 arm_dt_init_cpu_maps+0x114/0x16c
[ 0.000000] DT /cpu 2 nodes greater than max cores 1, capping them
[ 0.000000] Modules linked in:
[ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.14.78 #1
[ 0.000000] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
[ 0.000000] CPU: All CPU(s) started in SVC mode.
[ 0.000000] Built 1 zonelists, mobility grouping on. Total pages: 260096
[ 0.000000] Kernel command line: console=ttymxc0,115200 consoleblank=0 display=video=mxcfb0:dev=lcd,1024x600@60,if=RGB24,bpp=32 gpumemsize=128 GPU3DMinClk=8 ldo-mode-activate=1 fec_mac=80:7A:7F:02:97:5D logoType=1 ubi.mtd=9 root=ubi0:rootfs ro rootfstype=ubifs rootflags=sync mtdparts=gpmi-nand:8m(boot),1m(mac),1m(parameter),8m(kernel),1m(dtb),25m(minimal_system),1m(tmpdata_partition),140m(user_partition),35m(sys_config_partition),500m(rootfs),-(update) hardwareID=0x36
[ 0.000000] logoType_setup enter s=1 logoType = 1
[ 0.000000] hardwareID_setup enter str=0x36
[ 0.000000] Genway: HGI16 project, phase 2.0.
[ 0.000000] PID hash table entries: 4096 (order: 2, 16384 bytes)
[ 0.000000] Dentry cache hash table entries: 131072 (order: 7, 524288 bytes)
[ 0.000000] Inode-cache hash table entries: 65536 (order: 6, 262144 bytes)
[ 0.000000] Memory: 697856K/1048576K available (8192K kernel code, 431K rwdata, 2576K rodata, 1024K init, 413K bss, 23040K reserved, 327680K cma-reserved, 0K highmem)
[ 0.000000] Virtual kernel memory layout:
[ 0.000000] vector : 0xffff0000 - 0xffff1000 ( 4 kB)
[ 0.000000] fixmap : 0xffc00000 - 0xfff00000 (3072 kB)
[ 0.000000] vmalloc : 0xc0800000 - 0xff800000 (1008 MB)
[ 0.000000] lowmem : 0x80000000 - 0xc0000000 (1024 MB)
[ 0.000000] pkmap : 0x7fe00000 - 0x80000000 ( 2 MB)
[ 0.000000] modules : 0x7f000000 - 0x7fe00000 ( 14 MB)
[ 0.000000] .text : 0x80008000 - 0x80900000 (9184 kB)
[ 0.000000] .init : 0x80c00000 - 0x80d00000 (1024 kB)
[ 0.000000] .data : 0x80d00000 - 0x80d6bea0 ( 432 kB)
[ 0.000000] .bss : 0x80d6d000 - 0x80dd44d4 ( 414 kB)
[ 0.000000] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
[ 0.000000] Preemptible hierarchical RCU implementation.
[ 0.000000] Tasks RCU enabled.
[ 0.000000] NR_IRQS: 16, nr_irqs: 16, preallocated irqs: 16

I have tried many times, when these logs occur
20190820_11:19:25[ 938.505514] cma: cma_alloc: alloc failed, req-size: 765 pages, ret: -12
20190820_11:19:25[ 938.512150] mxc_vpu 2040000.vpu_fsl: Physical memory allocation error!
20190820_11:19:25[ 938.520212] mxc_vpu 2040000.vpu_fsl: Physical memory allocation error!
20190820_11:19:25[ 938.529687] cma: cma_alloc: alloc failed, req-size: 765 pages, ret: -12
20190820_11:19:25[ 938.536879] mxc_vpu 2040000.vpu_fsl: Physical memory allocation error!
20190820_11:19:25[ 938.543416] mxc_vpu 2040000.vpu_fsl: Physical memory allocation error!

Use command:
for n in 1 2 3 ; do echo $n > /proc/sys/vm/drop_caches ; done
will never solve the problem. before we execute the command,
20190820_11:19:44root@imx6solosabresd:/tmp/runnn# free -h
20190820_11:19:44 total used free shared buff/cache available
20190820_11:19:44Mem: 1.0G 474M 204M 5.2M 323M 511M
20190820_11:19:44Swap: 0B 0B 0B

After execute the command,

20190820_11:19:52[ 965.838359] sh (858): drop_caches: 1
20190820_11:19:52[ 965.871851] sh (858): drop_caches: 2
20190820_11:19:52[ 965.890224] sh (858): drop_caches: 3
20190820_11:19:54[ 965.890224]abresd:/tmp/runnn# free -h
20190820_11:19:55root@imx6solosabresd:/tmp/runnn# free -h
20190820_11:19:55 total used free shared buff/cache available
20190820_11:19:55Mem: 1.0G 472M 476M 2.0M 53M 517M
20190820_11:19:55Swap: 0B 0B 0B

We can see the cache has been released, but we still failed to allocate physical memory,and if we try to play again, the same message we get as the following,

20190820_11:20:00[ 974.003600] cma: cma_alloc: alloc failed, req-size: 149 pages, ret: -12
20190820_11:20:00[ 974.010234] mxc_vpu 2040000.vpu_fsl: Physical memory allocation error!
20190820_11:20:00[ 974.020861] mxc_vpu 2040000.vpu_fsl: Physical memory allocation error!
20190820_11:20:00[ 974.030328] cma: cma_alloc: alloc failed, req-size: 149 pages, ret: -12
20190820_11:20:00[ 974.037348] mxc_vpu 2040000.vpu_fsl: Physical memory allocation error!
20190820_11:20:00[ 974.044350] mxc_vpu 2040000.vpu_fsl: Physical memory allocation error!