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    SubjectRe: [BUG] Fwd: segfault : modprobe dccp_probe/tcp_probe
    On 6/7/07, Chuck Ebbert <cebbert@redhat.com> wrote:
    > On 06/06/2007 04:47 PM, Ian McDonald wrote:
    > > Hi there,
    > >
    > > We've seen a report of a problem with dccp_probe as shown below. The
    > > user has also verified that it occurs in tcp_probe as well. This is on
    > > Dave Miller's tree but that currently tracks Linus' tree quite
    > > closely. I do note that it is around 2.6.22-rc2 timeframe so there is
    > > a possibility fixes may have gone in since.
    > >
    >
    > It faulted when it tried to write the breakpoint instruction into the
    > running kernel's executable code. Apparently the kernel code is now marked
    > read-only?
    >
    >
    Yes it would appear to be the case as user has CONFIG_DEBUG_RODATA
    set. Patrick - can you turn this off and retest? It's under Kernel
    Hacking, Write protect kernel read only data structures.

    The list of commits that I see around this are at:
    http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git&a=search&h=HEAD&st=commit&s=DEBUG_RODATA

    I suspect it's probably one of the latter ones giving the timing.

    I guess there are a couple of solutions here - either make kprobes
    conflict with CONFIG_DEBUG_RODATA so you can do one or the other, or
    look into more detail what access kprobes need.

    Ian
    --
    Web: http://wand.net.nz/~iam4/
    Blog: http://iansblog.jandi.co.nz
    WAND Network Research Group
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