From: Jason Baron <jbaron@akamai.com>
To: Michael Ellerman <mpe@ellerman.id.au>,
Sachin Sant <sachinp@linux.vnet.ibm.com>,
Steven Rostedt <rostedt@goodmis.org>
Cc: linux-next@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
linuxppc-dev@ozlabs.org
Subject: Re: next-20170217 boot on POWER8 LPAR : WARNING @kernel/jump_label.c:287
Date: Wed, 22 Feb 2017 10:11:18 -0500 [thread overview]
Message-ID: <44116d94-20f8-29e1-5046-1f8c49fb67ed@akamai.com> (raw)
In-Reply-To: <877f4in5tn.fsf@concordia.ellerman.id.au>
On 02/22/2017 12:38 AM, Michael Ellerman wrote:
> Jason Baron <jbaron@akamai.com> writes:
>
>> On 02/20/2017 10:05 PM, Sachin Sant wrote:
>>>
>>>> On 20-Feb-2017, at 8:27 PM, Jason Baron <jbaron@akamai.com
>>>> <mailto:jbaron@akamai.com>> wrote:
>>>>
>>>> Hi,
>>>>
>>>> On 02/19/2017 09:07 AM, Sachin Sant wrote:
>>>>> While booting next-20170217 on a POWER8 LPAR following
>>>>> warning is displayed.
>>>>>
>>>>> Reverting the following commit helps boot cleanly.
>>>>> commit 3821fd35b5 : jump_label: Reduce the size of struct static_key
>>>>>
>>>>> [ 11.393008] ------------[ cut here ]------------
>>>>> [ 11.393031] WARNING: CPU: 5 PID: 2890 at kernel/jump_label.c:287
>>>>> static_key_set_entries.isra.10+0x3c/0x50
>>>>
>>>> Thanks for the report. So this is saying that the jump_entry table is
>>>> not at least 4-byte aligned. I wonder if this fixes it up?
>>>>
>>>
>>> Yes. With this patch the warning is gone.
>>
>> Hi,
>>
>> Thanks for testing. We probably need something like the following to
>> make sure we don't hit this on other arches. Steve - I will send 4
>> separate patches for this to get arch maintainers' acks for this?
>
> What's the 4 byte alignment requirement from?
>
The 4 byte alignment is coming from this patch in linux-next:
https://lkml.org/lkml/2017/2/3/558
It reduces the size of 'struct static_key' by making use of the two
least significant bits of the static_key::entry pointer. Thus, the
jump_entry table needs to be 4 byte aligned to make it work. I added a
WARN_ON() to make sure the jump_entry table is in fact 4 byte aligned,
and that is what we hit here.
> On 64-bit our JUMP_ENTRY_TYPE is 8 bytes, should we be aligning to 8
> bytes?
>
4 bytes should be sufficient and apparently fixes the WARN_ON() that was
hit.
>> diff --git a/arch/powerpc/include/asm/jump_label.h
>> b/arch/powerpc/include/asm/jump_label.h
>> index 9a287e0ac8b1..f870a85bac46 100644
>> --- a/arch/powerpc/include/asm/jump_label.h
>> +++ b/arch/powerpc/include/asm/jump_label.h
>> @@ -24,6 +24,7 @@ static __always_inline bool arch_static_branch(struct
>> static_key *key, bool bran
>> asm_volatile_goto("1:\n\t"
>> "nop # arch_static_branch\n\t"
>> ".pushsection __jump_table, \"aw\"\n\t"
>> + ".balign 4 \n\t"
>
> Can you line those up vertically?
>
> (That may just be an email artifact)
sure will fix.
Thanks,
-Jason
>
>> JUMP_ENTRY_TYPE "1b, %l[l_yes], %c0\n\t"
>> ".popsection \n\t"
>> : : "i" (&((char *)key)[branch]) : : l_yes);
>> @@ -38,6 +39,7 @@ static __always_inline bool
>> arch_static_branch_jump(struct static_key *key, bool
>> asm_volatile_goto("1:\n\t"
>> "b %l[l_yes] # arch_static_branch_jump\n\t"
>> ".pushsection __jump_table, \"aw\"\n\t"
>> + ".balign 4 \n\t"
>> JUMP_ENTRY_TYPE "1b, %l[l_yes], %c0\n\t"
>> ".popsection \n\t"
>> : : "i" (&((char *)key)[branch]) : : l_yes);
>> @@ -63,6 +65,7 @@ struct jump_entry {
>> #define ARCH_STATIC_BRANCH(LABEL, KEY) \
>> 1098: nop; \
>> .pushsection __jump_table, "aw"; \
>> + .balign 4; \
>> FTR_ENTRY_LONG 1098b, LABEL, KEY; \
>> .popsection
>> #endif
>
> Otherwise that looks fine assuming 4 bytes is the correct alignment.
>
> cheers
>
next prev parent reply other threads:[~2017-02-22 15:11 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-19 14:07 next-20170217 boot on POWER8 LPAR : WARNING @kernel/jump_label.c:287 Sachin Sant
2017-02-20 14:57 ` Jason Baron
[not found] ` <02B52EFB-4608-47F3-A81C-B8B52DB11233@linux.vnet.ibm.com>
2017-02-21 16:37 ` Jason Baron
2017-02-22 5:38 ` Michael Ellerman
2017-02-22 15:11 ` Jason Baron [this message]
2017-02-27 15:22 ` Steven Rostedt
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