Re: [PATCH] jump_label: align jump_entry table to at least 4-bytes

[David Daney]

On 02/28/2017 10:34 PM, Michael Ellerman wrote:
> Jason Baron <jbaron@xxxxxxxxxx> 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.


The original "balign patch" has a couple of problems:

1) 4-byte alignment is not sufficient for 64-bit kernels

2) It is redundant if the linker script patch is accepted.


> cheers
>
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