On 03/01/2017 12:02 PM, Jason Baron wrote:

On 03/01/2017 11:40 AM, David Daney wrote:

quoted

On 02/28/2017 10:34 PM, Michael Ellerman wrote:

quoted

Jason Baron [off-list ref] writes:
...

quoted

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.

The linker script patch seems reasonable to me.

Maybe its worth adding a comment that the alignment is necessary because
the core jump_label makes use of the 2 lsb bits of its __jump_table
pointer due to commit:

3821fd3 jump_label: Reduce the size of struct static_key

Also, in the comment it says that it fixes an oops. We hit a WARN_ON()
not an oops, although bad things are likely to happen when the branch is
updated.

OK, I guess I will send a proper patch e-mail with an updated changelog 
with the improvements you suggest.

Thanks,
David.