2.6.20 kernel hang with USB drive and vfat doing ftruncate

From: Kumar Gala
Date: Fri Feb 16 2007 - 14:55:36 EST

I'm seeing an issue with a stock 2.6.20 kernel running on an embedded PPC. I've got a usb flash drive plugged in and the filesystem on the drive is vfat. Running with 64M and no swap.

If I execute a series of large (100M+) ftruncate() on the disk the kernel will hang and never return. It seems to be stuck in the idle loop().

The following is the test program I'm running:

#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>

void usage (void)
printf ("truncate_test <filename> <size>\n\n");

int main(int argc, char *argv[])
int fd, i;
int ret = 0;
unsigned int len;

if (argc != 3) {
printf("Invalid number of arguments\n\n");

fd = open(argv[1], O_CREAT|O_RDWR|O_TRUNC, S_IRWXU);
len = strtoul(argv[2], NULL, 0);

ret = ftruncate(fd, len);

if (ret)
printf ("ftruncate ret = %d %d\n", ret, errno);


return ret;

I usually run the following twice to get the hang state:

time ./trunc_test bar 100000000 &
time ./trunc_test baz 100000000 &

I was wondering if anyone had any suggestions on what to poke at next to try and figure out what is going on.

- k
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