Inserting Into Buffer Cache

Inserting Into Buffer Cache

[Erwin Can Sar]

Hi,

I'm trying to write a driver that can insert a dirty buffer of data into its
buffer cache (for a research project). My block device has a sectorsize of
512 and 512 sectors. For some reason inserting into sector 0 works
correctly, but sector 1 does not work. What happens is that __getblk never
returns and it seems like it is looping forever. I think that the culprit
is the loop inside __getblk_slow that will loop forever if grow_buffer
keeps failing. The problematic call is:

  bh = __getblk(bdev, 1, hardsect_size);

In order to figure out what's going on I've put more and more of that code
into my own driver, so that it is now:

static int sbd_temp(struct block_device *bdev)
{
  struct buffer_head *bh;
  bh = __find_get_block(bdev, 1, hardsect_size);
  if(!bh) {
    printk("Not Found\n");
    if(!grow_buffers(bdev, 1, hardsect_size)) {
      printk("Couldn't grow\n");
      return -1;
    }
  }
  brelse(bh);
  return 0;
}

Unfortunately this leads to an OOPS:

------------[ cut here ]------------
Dec 17 13:05:13 ubuntu kernel: kernel BUG at fs/buffer.c:1619!
Dec 17 13:05:13 ubuntu kernel: invalid operand: 0000 [#1]
Dec 17 13:05:13 ubuntu kernel: PREEMPT
Dec 17 13:05:13 ubuntu kernel: Modules linked in: sbd proc_intf freq_table
cpufreq_userspace cpufreq_powersave ipv6 af_packet orinoco_cs orinoco
hermes ds button ac battery yenta_socket pcmcia_core e100 eepro100 mii
snd_intel8x0m snd_intel8x0 snd_ac97_codec snd_pcm_oss snd_mixer_oss snd_pcm
snd_timer snd_page_alloc gameport snd_mpu401_uart snd_rawmidi snd_seq_device
snd soundcore uhci_hcd usbcorepciehp shpchp pci_hotplug intel_agp agpgart
pcspkr rtc md dm_mod parport_pc lp p arport tsdev ide_cd joydev evdev cdrom
mousedev psmouse ext3 jbd ide_generic piix ide_disk ide_core unix fan
thermal processor
Dec 17 13:05:13 ubuntu kernel: CPU:    0
Dec 17 13:05:13 ubuntu kernel: EIP:    0060:[set_bh_page+23/54]    Not
tainted
Dec 17 13:05:13 ubuntu kernel: EFLAGS: 00010216   (2.6.8.1)
Dec 17 13:05:13 ubuntu kernel: EIP is at set_bh_page+0x17/0x36
Dec 17 13:05:13 ubuntu kernel: eax: c108b700   ebx: c03358d0   ecx: c03358d0
  e dx: 2f4da5f9
Dec 17 13:05:13 ubuntu kernel: esi: 2f4da5f9   edi: d0b26a07   ebp: 00000000
  e sp: cd30be94
Dec 17 13:05:13 ubuntu kernel: ds: 007b   es: 007b   ss: 0068
Dec 17 13:05:13 ubuntu kernel: Process simple (pid: 4534,
threadinfo=cd30a000 task=c315c3f0)
Dec 17 13:05:13 ubuntu kernel: Stack: c0146874 c03358d0 c108b700 2f4da5f9
c108b700 00000001 00000000 d0b26a07
Dec 17 13:05:13 ubuntu kernel:        c014698b c108b700 d0b26a07 00000000
00000001 00000000 00000000 d0b26a07
Dec 17 13:05:13 ubuntu kernel:        c0148a5f cf561080 00000001 00000000
00000001 d0b26a07 00000001 00000200
Dec 17 13:05:13 ubuntu kernel: Call Trace:
Dec 17 13:05:13 ubuntu kernel:  [create_buffers+88/144]
create_buffers+0x58/0x90Dec 17 13:05:13 ubuntu kernel: 
[grow_dev_page+119/264] grow_dev_page+0x77/0x108Dec 17 13:05:13 ubuntu
kernel:  [grow_buffers+79/148] grow_buffers+0x4f/0x94
Dec 17 13:05:13 ubuntu kernel:  [__crc___bitmap_andnot+8756634/10939662]
sbd_temp+0x5f/0x81 [sbd]
Dec 17 13:05:13 ubuntu kernel:  [__crc___bitmap_andnot+8757248/10939662]
sbd_ioctl+0x244/0x30b [sbd]
Dec 17 13:05:13 ubuntu kernel:  [blkdev_ioctl+838/859]
blkdev_ioctl+0x346/0x35bDec 17 13:05:13 ubuntu kernel:  [block_ioctl+26/30]
block_ioctl+0x1a/0x1e
Dec 17 13:05:13 ubuntu kernel:  [sys_ioctl+461/532] sys_ioctl+0x1cd/0x214
Dec 17 13:05:13 ubuntu kernel:  [sysenter_past_esp+82/113]
sysenter_past_esp+0x52/0x71
Dec 17 13:05:13 ubuntu kernel: Code: 0f 0b 53 06 22 e0 25 c0 2b 05 30 64 34
c0 c 1 f8 05 c1 e0 0c

Is there some problem with the way I am using __getblk? I've been spending a
lot of time on trying to figure this, but can't see what's wrong with my
code.
Thank you very much for your help,
Can Sar