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SubjectRe: [PATCH] Introduce freeze_super and thaw_super for the fsfreeze ioctl
Hi.

On 24/03/10 10:18, Al Viro wrote:
> On Wed, Mar 24, 2010 at 09:31:51AM +1100, Nigel Cunningham wrote:
>> /**
>> * freeze_filesystems - lock all filesystems and force them into a
>> consistent
>> * state
>> * @which: What combination of fuse& non-fuse to freeze.
>> */
>> void freeze_filesystems(int which)
>> {
>> struct super_block *sb;
>>
>> lockdep_off();
>>
>> /*
>> * Freeze in reverse order so filesystems dependant upon others are
>> * frozen in the right order (eg. loopback on ext3).
>> */
>
> [snip the horror]
>
> a) traversing superblock list without any locking whatsoever
> b) accessing superblock fields<....>
> c)<.........................> without making sure that it's not
> going to disappear
> d) calling freeze_bdev() without any warranties that its argument
> is not going to be freed under you
> e) layering violations all over the place
> etc.
>
> I've stayed away from TuxOnIce flamefests and I've no idea how representative
> that snippet is, but if it *does* match the general code quality in there...
> Ouch.

Locking isn't necessary because of the freezing.

Regards,

Nigel


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