On 02/22/2017 12:38 AM, Michael Ellerman wrote: > Jason Baron <jbaron@xxxxxxxxxx> writes: > >> On 02/20/2017 10:05 PM, Sachin Sant wrote: >>> >>>> On 20-Feb-2017, at 8:27 PM, Jason Baron <jbaron@xxxxxxxxxx >>>> <mailto:jbaron@xxxxxxxxxx>> 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 > -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
