Hi,
I have found a memory leak in the TI EDMA driver, which happens every
time a DMA transfer is performed.
The leak is in kernel 3.17, however the same problem seems to exist also
in 3.19.
In particular this was found on our custom TI AM1808 based hardware
while accessing the MMC/SD card interface.
When extensively using the SD card (e.g. downloading files to it) you
can virtually see the "SUnreclaim" memory in /proc/meminfo growing few
kB every few seconds.
After few days of operation a device with 128MB of RAM renders unusable
(lack of memory, system slow, processes being killed, etc.), the
unreclaimed SLAB memory is over 50MB.
The kernel memory leak debug mechanism revealed the leak to happen in
edma_prep_slave_sg(), however the same pattern repeats all over the
edma.c file (see below).
unreferenced object 0xc5abe3c0 (size 128):
comm "mmcqd/0", pid 1099, jiffies 4294948151 (age 5865.330s)
hex dump (first 32 bytes):
b7 02 00 00 03 00 00 00 00 00 00 00 80 bb 81 c7 ................
18 b4 23 c0 00 00 00 00 00 00 00 00 00 00 00 00 ..#.............
backtrace:
[<c023c8d0>] edma_prep_slave_sg+0x98/0x344
[<c030b350>] mmc_davinci_request+0x3d4/0x53c
[<c02f86c8>] mmc_start_request+0xc4/0xe8
[<c02f9654>] mmc_start_req+0x18c/0x354
[<c0307c84>] mmc_blk_issue_rw_rq+0xc0/0xc94
[<c0308a0c>] mmc_blk_issue_rq+0x1b4/0x4f4
[<c0309648>] mmc_queue_thread+0xb8/0x168
[<c0034930>] kthread+0xb4/0xd0
[<c0009730>] ret_from_fork+0x14/0x24
[<ffffffff>] 0xffffffff
The structure edma_desc is allocated using kzalloc in the
edma_prep_slave_sg() function, then a pointer to a member of its
substructure (dma_async_tx_descriptor) is returned.
Therefore the edma_desc structure cannot be freed since the allocated
address is nowhere stored and therefore lost.
I also haven't found that the dma_async_tx_descriptor would be freed,
but not sure whether the kernel does this in some other place?
Basically every time there is edma_prep_slave_sg 128 bytes of memory is
allocated but it's never freed.
I'm not sure what is the right way to fix this issue, but it seems to me
that the driver needs a more significant change to keep e.g. a pool of
resources which is reused and eventually freed, like some other EDMA
drivers do.
Could you please advise what to do.
Thank you
Petr
--
Petr Kulhavy, MSc
System Architect
Barix AG, Zürich, Switzerland
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