Re: ReiserFS buglet

[Jakob Oestergaard]

On Tue, Sep 24, 2002 at 01:21:10PM +0400, Oleg Drokin wrote:
> Hello!
> 
...
> 
> > I would suggest replacing the '!=' with a '<' in the while loop and
> > adding a sanity check afterwards.
> 
> What if overheated CPU will cause a bitflip exactly after such checks?
> You cannot protect against broken hardware. Such problems should be
> fixed by fsck.

Disk errors are common. Software can also flip that bit.

But I agree that it shouldn't be something that commonly happens, and I
suppose it is acceptable for a filesystem to barf if it has been
corrupted by malicious software.

> 
> > As I see it, the ReiserFS journal has the same problems as jbd wrt. to
> > atomicity of write operations of indexes.  Please see my recent mail
> > about the jbd problems.
> 
> journal header in reiserfs only occupies first 20 bytes of the block,
> since this fells within 1st 512 bytes hardware sector, it will be written
> atomically, I presume.

You presume wrong.

I posted to LKML about a month ago with some questions regarding exactly
this issue.  I had a disk that worked on 128 byte atomic writes - a
standard IDE disk.

The conclusion was something like "we know jack about the disk's
internal logic" so we need consistency measures instead of relying on
anything from the disk.

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