Kernel Panic in reading raw devices

[Shesha Sreenivasamurthy]

Hi All,
  In the user program below, I am trying to open, read, and close raw 
devices. The block devices sda-sdi are mapped to raw1-raw9. If a disk is 
missing, then after I get a read error I close that devices, remove that 
device from the proc file system and go on reading the next device. At 
this point, while I try to read from the next device (next disk after 
the missing one), kernel calls a BUG!! in bdput() inside 
"fs/block_dev.c".   If I postpone closing the missing disk (line 75) by 
storing the device handler of the missing disk in an integer array, and 
closing it after the loop (at line 87) then everying works well. I could 
not find an explanation for this phenomenon. Can any one please help me 
understand this.....

-Shesha

-------------------------------------------------------------------------------------------------------------
    1  #include <string.h>
    2  #include <sys/types.h>
    3  #include <unistd.h>
    4  #include <sys/stat.h>
    5  #include <fcntl.h>
    6  #include <linux/fs.h>
    7  #include <signal.h>
    8  #include <syslog.h>
    9  #include <stdio.h>
   10
   11
   12
   13  /* Raw devices require the memory to be aligned at sector boundry */
   14
   15  char * allign_memory(char * buffer, int boundry)
   16  {
   17      unsigned long addrs, rem;
   18      char * buf=buffer;
   19      addrs=(unsigned long)buffer;
   20      rem=addrs%boundry;
   21
   22      if(rem)
   23        buf = ((char *) addrs+(boundry-rem));
   24     return buf;
   25  }
   26
   27
   28  void scsi_single_dev(char *cmd, int host, int channel, int id, 
int lun)
   29  {
   30    FILE *fd;
   31
   32    fd = fopen("/proc/scsi/scsi", "w");
   33
   34    if (fd != NULL)
   35    {
   36      fprintf(fd, "scsi %s-single-device %d %d %d %d",
   37          cmd, host, channel, id, lun);
   38      fclose(fd);
   39      printf("scsi-single %s for %d:%d:%d:%d",cmd, host, channel, 
id, lun);
   40    }
   41    else
   42      printf("could not open /proc/scsi/scsi for 
%s-single-device", cmd);
   43  }
   44
   45  int main() {
   46
   47          char *t_buf=NULL, *buf=NULL;
   48          int dev=-1, rc=-1,i=1;
   49          char devname[16];
   50          int bad[10];
   51          int cnt=-1;
   52
   53          t_buf=(char *) malloc(4096+512);
   54
   55          if(t_buf) {
   56
   57          /* Raw devices require the memory to be aligned at 
sector boundry */
   58          buf=allign_memory(t_buf, 512);

   59          while(i<10) {
   60          printf("ITERATION : %d\n", i);
   61          sprintf(devname,"/dev/raw/raw%d",i);
   62          printf("RAW DEV NAME = %s\n", devname);
   63
   64          dev = open(devname, O_RDWR);
   65          printf("DEV Handler =%d\n", dev);
   66          rc = ioctl(dev, BLKFLSBUF, 0);
   67
   68          if(dev != -1) {
   69            rc = lseek(dev, 0, SEEK_SET);
   70            printf("RC lseek =%d\n", rc);
   71             if(rc != -1)
   72               rc=read(dev, buf, 4096);
   73                 printf("RC read =%d\n", rc);
   74
   75          close(dev);
   76
   77          if(rc==-1)
   78           scsi_single_dev("remove", 0, 0, i,  0);
   79
   80           }
   81           i++;
   82          }
   83         } else
   84            printf("tbuf NULL\n");
   85
   86          free(t_buf);
   87          return 0;
   88
   89  }
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