Re: Error testing ext3 on brd ramdisk

["Jorge Boncompte [DTI2]" <jorge@dti2.net>]

Nick Piggin escribió:
> On Thu, Mar 05, 2009 at 10:19:46AM +0100, Jorge Boncompte [DTI2] wrote:
>> -----------
>> umount /etc (/etc is what is mounted from /dev/ram0)
>> dd if=/dev/zero of=/dev/ram0 bs=1k count=1000
>> mount /dev/ram0 /etc -t minix -o rw
>> -----------
>> ...succeds and mounts a corrupted filesystem with the old content. Doing 
>> the same with the all ramdisk driver fails on mount with "no filesystem 
>> found".
>>
>> If I do...
>> -----------
>> umount /etc (/etc is what is mounted from /dev/ram0)
>> echo 3 > /proc/sys/vm/drop_caches
>> dd if=/dev/zero of=/dev/ram0 bs=1k count=1000
>> mount /dev/ram0 /etc -t minix -o rw
>> ----------
>> ... then the mount fails with no filesystem found as it should.
> 
> I can't reproduce this. Is the filesystem definitely being
> unmounted and nothing else is holding the bdev inode open?

	I don't know about the bdev inode :-( but I am sure that in 
/proc/mounts does not appear as listed.

> I can only imagine something like this happening if the fs
> is still mounted, in which case it will write back some
> superblock over the zeroed bdev, possibly allowing it to mount
> again, or if the zeroed writes somehow get lost, which would
> seem like a problem with the buffer cache.
> 
> Actually, the 2nd scenario is more likely, because you wouldn't
> see it with the old rd driver because it never allows the buffer
> cache to be freed.
> 
> Are you getting any errors in your dmesg or anything like that?

	No until I try to mount the filesystem again, then minix starts to 
complain.
-----------------
minix_free_block (ram0:38): bit already cleared
init_special_inode: bogus i_mode (0)
init_special_inode: bogus i_mode (0)
init_special_inode: bogus i_mode (0)
init_special_inode: bogus i_mode (0)
init_special_inode: bogus i_mode (0)
.........
-----------------

> What happens when you run the following patch? Can you run the
> test case then when you reproduce the problem, see if anything is
> in dmesg?

After a successful save
------------------
Mar  5 13:34:34 system: configuration save requested by user=root
Mar  5 13:34:34 kernel: syncing bdev
Mar  5 13:34:34 kernel: syncing bdev
Mar  5 13:34:34 kernel: syncing bdev
Mar  5 13:34:34 kernel: syncing bdev
Mar  5 13:34:34 kernel: killing bdev
Mar  5 13:34:34 kernel: syncing bdev
Mar  5 13:34:34 kernel: truncated bdev
Mar  5 13:34:34 kernel: killing bdev
Mar  5 13:34:34 kernel: syncing bdev
Mar  5 13:34:34 kernel: truncated bdev
Mar  5 13:34:34 kernel: killing bdev
Mar  5 13:34:34 kernel: syncing bdev
Mar  5 13:34:34 kernel: truncated bdev
Mar  5 13:34:34 kernel: killing bdev
Mar  5 13:34:34 kernel: syncing bdev
Mar  5 13:34:34 kernel: truncated bdev
Mar  5 13:34:34 kernel: killing bdev
Mar  5 13:34:34 kernel: syncing bdev
Mar  5 13:34:34 kernel: truncated bdev
Mar  5 13:34:34 kernel: killing bdev
Mar  5 13:34:34 kernel: syncing bdev
Mar  5 13:34:35 kernel: truncated bdev
Mar  5 13:34:35 kernel: killing bdev
Mar  5 13:34:35 kernel: syncing bdev
Mar  5 13:34:35 kernel: truncated bdev
Mar  5 13:34:35 kernel: killing bdev
Mar  5 13:34:35 kernel: syncing bdev
Mar  5 13:34:35 kernel: truncated bdev
------------------

rm -f <some archives>

------------------
Mar  5 13:35:00 system: configuration save requested by user=root
Mar  5 13:35:00 kernel: syncing bdev
Mar  5 13:35:00 kernel: syncing bdev
Mar  5 13:35:00 kernel: syncing bdev
Mar  5 13:35:00 kernel: syncing bdev
------------------

-- 
==============================================================
Jorge Boncompte - Ingenieria y Gestion de RED
DTI2 - Desarrollo de la Tecnologia de las Comunicaciones
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