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    SubjectRe: [2.6.27.24] Kernel coredump to a pipe is failing
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    On Tue, 2009-05-26 at 22:31 +0200, Andi Kleen wrote:
    > Paul Smith <paul@mad-scientist.net> writes:
    > > Well, -512 is ERESTARTSYS. That, to me, seems like a reasonable error
    > > code to get when we're trying to dump core to a pipe. Yes? No?
    >
    > Which signal is it? SIGPIPE?

    I'm not sure; I'll have to dig in a little further. I'm not sure
    offhand how to determine which signal it was from inside the kernel but
    it shouldn't be hard to find.

    > >
    > > Shouldn't we be doing some kind of error handling here, at least for
    > > basic things like signals? Should a process that's dumping core be set
    > > to ignore signals? Should dump_write() try again on ERESTARTSYS?
    >
    > I think it should block signals. Here's a untested patch.
    >
    > It has the disadvantage that it reports the incorrect blocked mask
    > in the ELF corefile, but that's probably better than truncated
    > coredumps.

    As a quick test I changed dump_write() to retry on ERESTARTSYS after
    disabling the pending signal, like:

    static int dump_write(struct file *file, const void *addr, int nr)
    {
    while (1) {
    int r = file->f_op->write(file, addr, nr, &file->f_pos);
    if (r != -ERESTARTSYS)
    return r == nr;

    /* We don't handle signals while dumping core. */
    clear_thread_flag(TIF_SIGPENDING);
    }
    }

    I don't know if this is right, but in some quick tests I ran it did
    work: my cores were full size. I haven't finished testing (and I have
    to go to soccer practice right now).

    This obviously doesn't reset the signal mask in the dumping process, but
    it makes the dump_write() more complex and it may cause other issues so
    I can't say whether this is the way to go.

    > -
    > Block signals during core dump

    Cool, I'll test this one as well.



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