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    SubjectRe: [PROBLEM] hard-lock with kmemtrace, relayfs, and splice
    On Fri, Oct 10, 2008 at 12:42:03PM +0300, Pekka Enberg wrote:
    > (I'm cc'ing Tom, Jens, and LKML.)
    >
    > On Fri, 2008-10-10 at 12:10 +0300, Pekka Enberg wrote:
    > > > I'm seeing a hard lock on my machine when I run kmemtraced with the
    > > > following patch applied:
    > > >
    > > > http://git.kernel.org/?p=linux/kernel/git/penberg/slab-2.6.git;a=commitdiff;h=17ca1d5506b1db433f0b7167a627bfd55d319dd3
    > > >
    > > > I can enable/disable kmemtrace via the debugfs files fine and can also
    > > > read the relay files with cat.
    > > >
    > > > Any idea where this is coming from?
    > >
    > > OK, it's the first splice() call in reader_thread() that causes the
    > > hang. Hmm.
    >
    > To recap, with a CONFIG_KMEMTRACE enabled kernel from the
    > "topic/kmemtrace" branch of:
    >
    > git://git.kernel.org/pub/scm/linux/kernel/git/penberg/slab-2.6.git topic/kmemtrace
    >
    > running the "kmemtraced" program from
    >
    > git://git.kernel.org/pub/scm/linux/kernel/git/penberg/kmemtrace-user.git
    >
    > results to a hard lock on my machine. I am unable to find anything
    > obviously wrong with it and as I can read/write the relay files just
    > fine, I'm beginning to think it's problem in relayfs splice
    > implementation.
    >
    > Tom, thoughts?
    >
    > Pekka
    >

    Hmm, I've seen kmemtraced not stopping, but no hard locks. It seems not
    even SIGKILL can stop it. As far as I know, SIGKILL should stop even a
    blocking splice() (in case this is the problem). This is what I did:
    # ./kmemtraced &
    # killall -KILL kmemtraced
    ... kmemtraced still running and using CPU.


    Eduard



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