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    SubjectRe: [GIT PULL] Please pull NFS client bugfixes....
    On Thu, Jan 07, 2010 at 07:14:42PM -0500, Trond Myklebust wrote:
    > On Fri, 2010-01-08 at 00:51 +0100, Andi Kleen wrote:
    > > > I'd like to see this fixed, but I do not want to jump onto a solution
    > > > that changes the behaviour of mmap() w.r.t. revalidation. The current
    > > > behaviour dates back at least to 2.3.x if not before.
    > >
    > > So do you have a plan to fix it?
    >
    > Yes. I want to pursue Peter Zijlstra's patches, which split up the mmap
    > function into a set of parts which require the mmap_sem, and other parts
    > which don't, and that adds a filesystem callback that allows for
    > revalidation to occur outside the mmap_sem.

    Is that really a 2.6.33 solution?

    It sounds intrusive.

    >
    > > I don't think it'll be possible to do drastic changes in the
    > > VFS for 2.6.33, and it seems preserving the current semantics
    > > would need that.
    > >
    > > > That's why I'm working slowly on this.
    > >
    > > Delaying a fix to after 2.6.33 is not an option imho.
    > >
    > > It hits everyone with LOCKDEP enabled who uses mmap over NFS.
    > > That's new in 2.6.33, previously LOCKDEP didn't diagnose this.
    > >
    > > I'll keep using my patch, but I suppose once we're going more
    > > towards a release you'll get more reports of this.
    >
    > Why should this particular issue require us to rush into a solution?

    Because every lockdep user NFS+mmap gets spammed now.

    That's like having an oops in the startup sequence. The system
    might still boot, but users are not happy.

    > This has been there for literally _years_, and I've never heard of a
    > single incident in which a deadlock actually occurred. The only reason
    > why we've noticed it at all is because lockdep has started to whine.

    I bet there were deadlocks somewhere, probably just didn't get reported.

    -Andi
    --
    ak@linux.intel.com -- Speaking for myself only.


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