linux-kernel - Re: [2.6.27.24] Kernel coredump to a pipe is failing

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Date:	Tue, 26 May 2009 12:33:54 -0400
From:	Paul Smith <paul@...-scientist.net>
To:	linux-kernel@...r.kernel.org
Subject: Re: [2.6.27.24] Kernel coredump to a pipe is failing

Sorry for not following up to my previous message to get the threading
headers correct: the original is on another system I don't have access
to and I can't find a way to reply from any of the web archived
versions.  Anyway, this is a link to the original FYI:

http://marc.info/?l=linux-kernel&m=124299629611706

In that post I observed that my short cores were being caused by
dump_write() returning 0; taking another look at dump_write():

        static int dump_write(struct file *file, const void *addr, int nr)
        {
        	return file->f_op->write(file, addr, nr, &file->f_pos) == nr;
        }

If the write operation returns an error of any kind, or it fails to
write the complete set of bytes (nr here is always PAGE_SIZE, as this
function is called when it fails), then dump_write() returns 0 and we
get a short core.

So I annotated dump_write() to printk() if this operation is false, and
I get:

        file ffff8803b95d0180: dump_write: -512 < 4096

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?

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?

Any advice or comments would be greatly appreciated!

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