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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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