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From
SubjectRe: [PATCH resend] introduce I_SYNC
Date
Hi,

On 16 May 2007, at 18:01, Jörn Engel wrote:
> Patches fixes a deadlock problem well enough for LogFS to survive.
> The
> problem itself is generic and seems to be ancient. Shaggy has code in
> JFS from about 2.4.20 that seems to work around the deadlock. Dave
> Chinner indicated that this could cause latency problems (not a
> deadlock) on the NFS server side.

I agree that your patch is a good idea. I reviewed the latest
incarnation and it makes sense to me. And your comment concerning
the flags is a very welcome addition. Probably ought to find its way
into Documentation/filesystems/Locking or vfs.txt or somewhere like
that also.

Note that once your patch is applied I think it would make sense to
follow up with a second patch to remove the I_LOCK flag completely.
The only remaining uses are either together with I_NEW in which case
I_LOCK can be removed altogether or can be substituted with I_NEW
when only I_LOCK is used. This is because no places remain where we
set I_LOCK by itself any more with your patch. The only place where
we set it is the place where a new inode gets created in memory and
in that place we also set I_NEW at the same time as I_LOCK.
wait_on_inode() can then be changed to wait on I_NEW instead of on
I_LOCKED. That way we have one less confusing flag to worry about
and things are much easier to understand.

> I still suspect that NTFS has hit the same deadlock and its current
> "fix" will cause data corruption instead.

The NTFS "fix" will not cause data corruption at all. The usage in
NTFS is very different... I am afraid your patch does not address
the deadlock with NTFS or rather it only addresses the inode write
deadlock and does not address the get_new_inode() deadlock that
exists with ilookup5() and is avoided by ilookup5_nowait(). This
deadlock is inherent to what NTFS does so you don't need to worry
about it. (If you want I am happy to explain it but I would rather
not waste my time explaining if no-one except me cares about it...)

Best regards,

Anton
--
Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK
Linux NTFS maintainer, http://www.linux-ntfs.org/


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