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    SubjectRe: nfs: infinite loop in fcntl(F_SETLKW)
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    On Fri, Apr 11, 2008 at 09:12:23PM +0200, Miklos Szeredi wrote:
    > > > OK. So the correct fix here should really be applied to fcntl_setlk().
    > > > There is absolutely no reason why we should be looping at all if the
    > > > filesystem has a ->lock() method.
    > > >
    > > > In fact, this looping behaviour was introduced recently in commit
    > > > 7723ec9777d9832849b76475b1a21a2872a40d20.
    > >
    > > Apologies, that was indeed a behavioral change introduced in a commit
    > > that claimed just to be shuffling code around.
    >
    > Yeah, that patch looks totally wrong. It's not generally a good idea
    > to do a loop where the exit condition depends on something you don't
    > control. And error values from filesystem methods are typically like
    > that. For example with fuse, the error code could come from an
    > unprivileged userspace process.
    >
    > I didn't realize this aspect of the bug previously, because I
    > concentrated on the lockd inconsistency.
    >
    > Btw, why hasn't this work been posted on -fsdevel prior to merging
    > into mainline?

    http://marc.info/?l=linux-fsdevel&m=117581629326194&w=2

    --b.

    >
    > >
    > > > Marc, Bruce, why was this
    > > > done, and how are filesystems now supposed to behave?
    > > >
    > >
    > > The assumption must have been that -EAGAIN could only mean that we
    > > needed to keep blocking, and hence was a nonsensical return from a
    > > filesystem lock method that waited itself for the lock to become
    > > available--such a method would return 0, -EINTR (or some more exotic
    > > error), or continue waiting.
    >
    > EAGAIN for a blocking lock is nonsensical, so my original patch could
    > still make sense. But that's no longer a regression, and not all that
    > important.


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