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    SubjectRe: [PROBLEM] hard-lock with kmemtrace, relayfs, and splice
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    Hi Pekka,

    On Mon, 2008-10-13 at 09:57 +0300, Pekka Enberg wrote:
    > Hi Tom,
    >
    > On Fri, 2008-10-10 at 23:58 -0500, Tom Zanussi wrote:
    > > It looks like you hit the same problem as described here:
    > >
    > > commit 8191ecd1d14c6914c660dfa007154860a7908857
    > >
    > > splice: fix infinite loop in generic_file_splice_read()
    > >
    > > relay uses the same loop but it never got noticed or fixed. Can you try
    > > the following patch:
    > >
    > > diff --git a/kernel/relay.c b/kernel/relay.c
    > > index 8d13a78..6a4d439 100644
    > > --- a/kernel/relay.c
    > > +++ b/kernel/relay.c
    > > @@ -1318,12 +1318,9 @@ static ssize_t relay_file_splice_read(struct file *in,
    > > if (ret < 0)
    > > break;
    > > else if (!ret) {
    > > - if (spliced)
    > > - break;
    > > - if (flags & SPLICE_F_NONBLOCK) {
    > > + if (flags & SPLICE_F_NONBLOCK)
    > > ret = -EAGAIN;
    > > - break;
    > > - }
    > > + break;
    > > }
    > >
    > > *ppos += ret;
    > >
    >
    > Indeed. That fixes the deadlock.
    >
    > However, now I don't get anything to the cpu*.out files if I run
    > kmemtraced with kmemtrace disabled. If I enable kmemtrace manually and
    > then run kmemtraced, I do receive some data. I did apply the
    > kmemtrace-user patch as well.
    >
    > Hmm?

    To me, that sounds like how it should work - if kmemtrace is disabled,
    it shouldn't be logging anything, and that's in fact what I saw when
    debugging this - it started out disabled and therefore nothing being
    logged to relay (printks confirmed that). When I wrote 1 to the enabled
    file, data started getting logged to relay and to the *.out files.

    So I don't know why the enabled state behaves the way it does, or if
    it's unexpected, but that anyway doesn't seem like a relay problem to
    me.

    Tom

    >
    > Pekka
    >



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