Re: Oops when unmounting a floppy (linux 2.4.13)

[BALBIR SINGH]

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Preliminary analysis shows that getblk now no longer holds lru_list_lock.
I am sure there is a good reason for that, I hope :-)

get_hash_table just holds hash_table_lock where as invalidate_buffer
holds lru_list_lock.

Comments from kernel code

/* Anti-deadlock ordering:
 *      lru_list_lock > hash_table_lock > unused_list_lock
 */

Notes from document on locks (lse.sourceforge.net)

Lock:           lru_list_lock
Interrupts:     Ignored
Functions:      sync_buffers(), buffer_insert_inode_queue(),
                inode_has_buffers(),  __invalidate_buffers(),
                set_blocksize(), fsync_inode_buffers(),
                osync_inode_buffers(), invalidate_inode_buffers(),
                getblk(), refile_buffers(), __bforget(),
                try_to_free_buffers(), show_buffers(),
                flush_dirty_buffers()
Use:            Held while reading or writing the lru_list.
Notes:          if hash_table_lock and  unused_list_lock are also used,
                then the order should be lru_list_lock --> hash_table_lock
                --> unused_list_lock to avoid deadlocks.  The routines
                __removed_from_queues() and __insert_into_queues()
                expect this lock to be held upon entry.

getblk() is no longer holding lru_list_lock, so I suspect this caused the
race, the fix I think is quite simple, hold the lru_list_lock in getblk()
and release it at the end.

Comments,
Balbir

Manuel Cepedello Boiso wrote:

>
>I've found a kernel oops when I tried to unmount a floppy under Linux
>2.4.13. The disquette has an HFS filesystem (Macintosh) and the support
>for the floppy was compiled as module.
>
>The kernel log is the following:
>
>Oct 31 12:59:43 cauchy kernel: inserting floppy driver for 2.4.13
>Oct 31 12:59:43 cauchy kernel: Floppy drive(s): fd0 is 1.44M
>Oct 31 12:59:43 cauchy kernel: FDC 0 is a post-1991 82077
>Oct 31 12:59:43 cauchy kernel: VFS: Disk change detected on device fd(2,0)
>Oct 31 13:01:34 cauchy kernel: kernel BUG at buffer.c:673!
>Oct 31 13:01:34 cauchy kernel: invalid operand: 0000
>Oct 31 13:01:34 cauchy kernel: CPU:    0
>Oct 31 13:01:34 cauchy kernel: EIP:    0010:[invalidate_bdev+157/312]
>Tainted: PF
>Oct 31 13:01:34 cauchy kernel: EFLAGS: 00010282
>Oct 31 13:01:34 cauchy kernel: eax: 0000001c   ebx: cd7025c0   ecx:
>c01fe6a0   edx: 000028d7
>Oct 31 13:01:34 cauchy kernel: esi: 00000001   edi: c0a295c0   ebp:
>00000000   esp: cf561ef8
>Oct 31 13:01:34 cauchy kernel: ds: 0018   es: 0018   ss: 0018
>Oct 31 13:01:34 cauchy kernel: Process umount (pid: 2436,
>stackpage=cf561000)
>Oct 31 13:01:34 cauchy kernel: Stack: c01d48bc 000002a1 c194a1e0 c300b860
>00000000 d4dd9244 02000000 00000000
>Oct 31 13:01:34 cauchy kernel:        00000000 c0131b59 c194a1e0 00000001
>c194a1e0 c013263a c194a1e0 d4dd9200
>Oct 31 13:01:34 cauchy kernel:        c194a1e0 00000200 c0131816 c194a1e0
>00000002 c180e460 d4dd9200 cf561f98
>Oct 31 13:01:34 cauchy kernel: Call Trace: [kill_bdev+13/40]
>[blkdev_put+78/144] [kill_super+250/316] [<e0995520>] [__mntput+30/36]
>Oct 31 13:01:34 cauchy kernel:    [path_release+39/44]
>[sys_umount+167/180] [sys_munmap+53/84] [sys_oldumount+12/16]
>[system_call+51/56]
>Oct 31 13:01:34 cauchy kernel:
>Oct 31 13:01:34 cauchy kernel: Code: 0f 0b 83 c4 08 8d b6 00 00 00 00 f6
>43 18 02 74 0d 68 c5 48
>
>
>
>Manuel Cepedello
>
>-
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