linux-kernel - Re: [PATCH v5 1/5] vmcore: Introduce ELF header in new memory feature

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Date:	Fri, 28 Jun 2013 10:15:52 +0200
From:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>,
	Jan Willeke <willeke@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org
Subject: Re: [PATCH v5 1/5] vmcore: Introduce ELF header in new memory
 feature

On Thu, 27 Jun 2013 16:23:34 -0400
Vivek Goyal <vgoyal@...hat.com> wrote:

> On Thu, Jun 27, 2013 at 03:32:02PM -0400, Vivek Goyal wrote:
> > On Fri, Jun 21, 2013 at 04:17:03PM +0200, Michael Holzheu wrote:
> > > On Fri, 14 Jun 2013 14:54:02 -0400
> > > Vivek Goyal <vgoyal@...hat.com> wrote:

[snip]

> Thinking more about it, I think let us cleanup with this little ugly
> bit too so that future changes become easy.
> 
> Current convention is that elfcorehdr_addr and elfcorehdr_size are
> already set by arch code by the time vmcore.c starts reading it. Can't
> s390 allocate elf headers in early boot code and elfcorehdr_addr? Then
> we don't have to call elfcorehdr_alloc().
> 
> And once we are done with reading headers, we can call elfcorehdr_free()
> and s390 could free memory and set elfcorehdr_addr to ELFCORE_ADDR_ERR
> and elfcorehdr_size=0. That would signify that one can not try to read
> elf headers now and it must have been freed.
> 
> is_kdump_kernel() will continue to work as elfcorehdr_addr is
> ELFCORE_ADDR_ERR. And that will mean that either elfcorehdr were not
> readable/usable to begin with or they have been freed now.

Hello Vivek,

We would like to keep the alloc/free symmetry as you have suggested in a
previous mail. This also has the advantage that we do not have to rely
on the ordering of init calls.

Wouldn't it be sufficient to just set elfcorehdr_addr to ELFCORE_ADDR_ERR
after elfcorehdr_free() and remove the comment?

So the code would look like the following:

static int __init vmcore_init(void)
{
        int rc = 0;

        /* Allow architectures to allocate ELF header in 2nd kernel */
        rc = elfcorehdr_alloc(&elfcorehdr_addr, &elfcorehdr_size);
        if (rc)
                return rc;
        /*
         * If elfcorehdr= has been passed in cmdline or created in 2nd kernel,
         * then capture the dump.
         */
        if (!(is_vmcore_usable()))
                return rc;
        rc = parse_crash_elf_headers();
        if (rc) {
                pr_warn("Kdump: vmcore not initialized\n");
                return rc;
        }
        elfcorehdr_free(elfcorehdr_addr);
	elfcorehdr_addr = ELFCORE_ADDR_ERR;

        proc_vmcore = proc_create("vmcore", S_IRUSR, NULL, &proc_vmcore_operations);
        if (proc_vmcore)
                proc_vmcore->size = vmcore_size;
        return 0;
}

This looks clean for me.

What do you think?

Best Regards,
Michael

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