I was testing the SD card support in the latest linux-davinci GIT tree.
I had read a file from SD and then written a file. Before removing the
SD card, I unmounted it (ext2 FS).
Here is the console output: umount command, info that the card removal
was detected, and the first bit of the kernel dump:
# umount /tmp/mnt
# mmc0: card b368 removed
davinci_mmc davinci_mmc.0: DMA read error
Unable to handle kernel NULL pointer dereference at virtual address
00000010
pgd = c0004000
[00000010] *pgd=00000000
Internal error: Oops: 817 [#1] PREEMPT
Modules linked in:
CPU: 0 Not tainted (2.6.30-davinci1-05997-g35265ab #7)
PC is at mmc_davinci_dma_cb+0x54/0x74
LR is at mmc_davinci_dma_cb+0x4c/0x74
pc : [<c01bbf30>] lr : [<c01bbf28>] psr: 20000013
sp : c0303ef8 ip : c0303e60 fp : 00000000
r10: 00000000 r9 : 00000001 r8 : 00002040
r7 : 00000300 r6 : 00000308 r5 : 00000000 r4 : c798a760
r3 : fffffffb r2 : 00000000 r1 : 80000013 r0 : 0000002d
Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment kernel
Control: 0005317f Table: 87a38000 DAC: 00000017
Process swapper (pid: 0, stack limit = 0xc0302268)
Stack: (0xc0303ef8 to 0xc0304000)
3ee0: 0000001b
c0030854
3f00: 00000011 00000000 c0332bd0 c7807b80 00000011 00000001 00000000
00000000
3f20: c0302000 8001ecb4 00000000 c00629a0 c0302000 c030b294 00000011
c7807b80
3f40: c0332bd0 c0064a60 00000011 00000000 c03065e4 00000002 00000001
c0026050
3f60: 00000001 ffffffff fec48000 c0026a0c 00000000 0005317f 0005217f
60000013
3f80: c0027ddc c0302000 c03065e4 c0027ddc c031e808 41069265 8001ecb4
00000000
3fa0: 600000d3 c0303fb8 c0027e1c c0027e28 60000013 ffffffff 00000000
c0027cc0
3fc0: c0332d5c c031e7dc c0020ee4 c0306430 8001ece8 c0008b60 c00084ec
00000000
3fe0: 00000000 c0020ee4 00053175 c031e838 c00212e8 80008034 00000000
00000000
[<c01bbf30>] (mmc_davinci_dma_cb+0x54/0x74) from [<c0030854>]
(dma_ccerr_handler+0xf0/0x1e4)
In looking in the vmlinux.o file, I found
00195edc l F .text 00000074 mmc_davinci_dma_cb
using objdump and going off of : PC is at mmc_davinci_dma_cb+0x54/0x74
0x52C + 0x54 - 0x580
0000052c <mmc_davinci_dma_cb>:
52c: e3510001 cmp r1, #1 ; 0x1
530: e92d4010 push {r4, lr}
534: e1a04002 mov r4, r2
538: 08bd8010 popeq {r4, pc}
53c: e5923008 ldr r3, [r2, #8]
540: e5930000 ldr r0, [r3]
544: ebfffffe bl 0 <dev_driver_string>
548: e5943004 ldr r3, [r4, #4]
54c: e5942008 ldr r2, [r4, #8]
550: e5933014 ldr r3, [r3, #20]
554: e1a01000 mov r1, r0
558: e3130c01 tst r3, #256 ; 0x100
55c: e5920000 ldr r0, [r2]
560: e59f302c ldr r3, [pc, #44] ; 594 <mmc_davinci_dma_cb+0x68>
564: e59f202c ldr r2, [pc, #44] ; 598 <mmc_davinci_dma_cb+0x6c>
568: 01a03002 moveq r3, r2
56c: e5902008 ldr r2, [r0, #8]
570: e59f0024 ldr r0, [pc, #36] ; 59c <mmc_davinci_dma_cb+0x70>
574: ebfffffe bl 0 <printk>
578: e5942004 ldr r2, [r4, #4]
57c: e3e03004 mvn r3, #4 ; 0x4
580: e5823010 str r3, [r2, #16]
584: e5941004 ldr r1, [r4, #4]
588: e1a00004 mov r0, r4
58c: e8bd4010 pop {r4, lr}
590: eaffffa0 b 418 <mmc_davinci_xfer_done>
I take it to mean the seg fault happened at
580: e5823010 str r3, [r2, #16]
The source routine is rather short
static void mmc_davinci_dma_cb(unsigned channel, u16 ch_status, void
*data)
{
if (DMA_COMPLETE != ch_status) {
struct mmc_davinci_host *host = data;
/* Currently means: DMA Event Missed, or "null" transfer
* request was seen. In the future, TC errors (like bad
* addresses) might be presented too.
*/
dev_warn(mmc_dev(host->mmc), "DMA %s error\n",
(host->data->flags & MMC_DATA_WRITE)
? "write" : "read");
host->data->error = -EIO;
mmc_davinci_xfer_done(host, host->data);
}
}
I found:
include/asm-generic/errno-base.h:#define EIO 5 /* I/O error */
so
57c: e3e03004 mvn r3, #4 ; 0x4
and reading that mvn is move NOT, which translates to -5 (0xFB) being
stored r3, meaning the C line that had a NULL pointer dereference is
host->data->error = -EIO;
Should mmc_davinci_dma_cb() check that host->data is not null?
Todd
P.S. I'm a bit confused as to why host->data->flags didn't fail first if
host->data is null.
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