linux-kernel - Re: [PATCH] jump_label: align jump

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Date:   Wed, 01 Mar 2017 17:34:51 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Jason Baron <jbaron@...mai.com>,
        David Daney <ddaney@...iumnetworks.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sachin Sant <sachinp@...ux.vnet.ibm.com>
Cc:     linux-mips@...ux-mips.org, Chris Metcalf <cmetcalf@...lanox.com>,
        Russell King <linux@...linux.org.uk>,
        Ralf Baechle <ralf@...ux-mips.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Rabin Vincent <rabin@....in>,
        Paul Mackerras <paulus@...ba.org>,
        Anton Blanchard <anton@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org, Ingo Molnar <mingo@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, Zhigang Lu <zlu@...hip.com>
Subject: Re: [PATCH] jump_label: align jump_entry table to at least 4-bytes

Jason Baron <jbaron@...mai.com> writes:
...
> I also checked all the other .ko files and they were properly aligned. 
> So I think this should hopefully work, and I like that its not a 
> per-arch fix.
>
> Sachin, sorry to bother you again, but I'm hoping you can try David's 
> latest patch to scripts/module-common.lds, just to test in your setup.

It does fix the problem.

I was reproducing with crc_t10dif:

[  695.890552] ------------[ cut here ]------------
[  695.890709] WARNING: CPU: 15 PID: 3019 at ../kernel/jump_label.c:287 static_key_set_entries+0x74/0xa0
[  695.890710] Modules linked in: crc_t10dif(+) crct10dif_generic crct10dif_common ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 xt_addrtype iptable_filter ip_tables xt_conntrack x_tables nf_nat nf_conntrack bridge stp llc dm_thin_pool dm_persistent_data dm_bio_prison dm_bufio libcrc32c kvm virtio_balloon binfmt_misc autofs4 virtio_net virtio_pci virtio_ring virtio

Which had:

  [21] __jump_table      PROGBITS        0000000000000000 0004e8 000018 00  WA  0   0  1


And now has:

  [18] __jump_table      PROGBITS        0000000000000000 0004d0 000018 00  WA  0   0  8

And all other modules have an alignment of 8 on __jump_table, as expected.

I'm inclined to merge a version of the balign patch for powerpc anyway,
just to be on the safe side. I guess the old code was coping fine with
the unaligned keys, but it still makes me nervous.

cheers