linux-kernel - Re: linux-next: build failure after merge of the printk tree

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Date:   Mon, 5 Mar 2018 13:27:48 +0800
From:   Greentime Hu <green.hu@...il.com>
To:     Dave Young <dyoung@...hat.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Petr Mladek <pmladek@...e.com>, Tejun Heo <tj@...nel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        akpm@...ux-foundation.org, Andi Kleen <ak@...ux.intel.com>
Subject: Re: linux-next: build failure after merge of the printk tree

2018-03-05 11:20 GMT+08:00 Dave Young <dyoung@...hat.com>:
> On 03/03/18 at 11:47pm, Sergey Senozhatsky wrote:
>> Cc-ing Tejun
>>
>> On (03/02/18 16:54), Petr Mladek wrote:
>> [..]
>> > > (Though it is not immediately obvious why.)
>> >
>> > It is a mistery to me. The error appears when I move any of
>> > dump_stack_print_info() or show_regs_print_info() function
>> > definitions from kernel/printk/printk.c to lib/dump_stack.c.
>> > All the other changes seems unrelated.
>> >
>> > The thing is that we basically do not touch dump_stack() definition
>> > by that patch.
>>
>> Apparently dump_stack_print_info() was in lib/dump_stack.c a long
>> time ago, but it was deliberately moved to printk.c, when kernel gained
>> a "generic" (dummy) dump_stack() fallback. Some archs, like blackfin,
>> define their own dump_stack() symbol and make it global via EXPORT_SYMBOL.
>>
>> In case of blackfin that arch-specific dump_stack() symbol invokes a
>> global dump_stack_print_info(). If we move dump_stack_print_info() back
>> to lib/dump_stack.c then we link both with arch/blackfin/dumpstack.o
>> and lib/dump_stack.o, which results in multiple definitions error.
>> If we move dump_stack_print_info() out on libdump_stack.o, then we
>> never link with lib/dump_stack.o
>>
>> ... so what are we going to do with that.
>>
>> a) we can drop the patch and cherry pick only the kexec part
>>
>> b) we can try to mark dummy lib/dump_stack() as __weak
>>    EXPORT_SYMBOL and remove EXPORT_SYMBOL from arch-specific
>>    definitions.
>>
>>    So we will end up with EXPORT_SYMBOL dump_stack() and archs
>>    may re-define it. If some arch will accidentally mark its
>>    own dump_stack() as EXPORT_SYMBOL then there should be a
>>    linkage warning - a symbol is exported twice.
>>
>>
>> Something like below.
>>
>> Opinions? Will this work?
>
> I would think b) is better, thanks for the fix!
>
Hi,

b works in nds32.
Thanks for the fix :)

>>
>>
>> ========= 8< =========
>>
>> From: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
>> Subject: [PATCH] dump_stack: mark dummy dump_stack() as weak
>>
>> ---
>>  arch/blackfin/kernel/dumpstack.c | 1 -
>>  arch/nds32/kernel/traps.c        | 2 --
>>  lib/dump_stack.c                 | 4 ++--
>>  3 files changed, 2 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/blackfin/kernel/dumpstack.c b/arch/blackfin/kernel/dumpstack.c
>> index 3c992c1f8ef2..61af017130cd 100644
>> --- a/arch/blackfin/kernel/dumpstack.c
>> +++ b/arch/blackfin/kernel/dumpstack.c
>> @@ -174,4 +174,3 @@ void dump_stack(void)
>>       show_stack(current, &stack);
>>       trace_buffer_restore(tflags);
>>  }
>> -EXPORT_SYMBOL(dump_stack);
>> diff --git a/arch/nds32/kernel/traps.c b/arch/nds32/kernel/traps.c
>> index 8828b4aeb72b..455bb0787367 100644
>> --- a/arch/nds32/kernel/traps.c
>> +++ b/arch/nds32/kernel/traps.c
>> @@ -166,8 +166,6 @@ void dump_stack(void)
>>       __dump(NULL, base_reg);
>>  }
>>
>> -EXPORT_SYMBOL(dump_stack);
>> -
>>  void show_stack(struct task_struct *tsk, unsigned long *sp)
>>  {
>>       unsigned long *base_reg;
>> diff --git a/lib/dump_stack.c b/lib/dump_stack.c
>> index 5cff72f18c4a..9cf4465dbffa 100644
>> --- a/lib/dump_stack.c
>> +++ b/lib/dump_stack.c
>> @@ -85,7 +85,7 @@ static void __dump_stack(void)
>>  #ifdef CONFIG_SMP
>>  static atomic_t dump_lock = ATOMIC_INIT(-1);
>>
>> -asmlinkage __visible void dump_stack(void)
>> +asmlinkage __weak __visible void dump_stack(void)
>>  {
>>       unsigned long flags;
>>       int was_locked;
>> @@ -118,7 +118,7 @@ asmlinkage __visible void dump_stack(void)
>>       local_irq_restore(flags);
>>  }
>>  #else
>> -asmlinkage __visible void dump_stack(void)
>> +asmlinkage __weak __visible void dump_stack(void)
>>  {
>>       __dump_stack();
>>  }
>> --
>> 2.16.2
>>
>
> Thanks
> Dave