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    SubjectRe: ReiserFS buglet
    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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