stressfs.c

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Demonstrate that moving the "acquire" in iderw after the loop that appends to the idequeue results in a race.

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For this to work, you should also add a spin within iderw's idequeue traversal loop. Adding the following demonstrated a panic after about 5 runs of stressfs in QEMU on a 2.1GHz CPU: for (i = 0; i < 40000; i++) asm volatile("");

#include "kernel/types.h"
#include "kernel/stat.h"
#include "user/user.h"
#include "kernel/fs.h"
#include "kernel/fcntl.h"

int
main(int argc, char *argv[])
{
  int fd, i;
  char path[] = "stressfs0";
  char data[512];

  printf("stressfs starting\n");
  memset(data, 'a', sizeof(data));

  for(i = 0; i < 4; i++)
    if(fork() > 0)
      break;

  printf("write %d\n", i);

  path[8] += i;
  fd = open(path, O_CREATE | O_RDWR);
  for(i = 0; i < 20; i++)

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printf(fd, "%d\n", i);

    write(fd, data, sizeof(data));
  close(fd);

  printf("read\n");

  fd = open(path, O_RDONLY);
  for (i = 0; i < 20; i++)
    read(fd, data, sizeof(data));
  close(fd);

  wait(0);

  exit(0);
}