linux-kernel - Re: [PATCH] dump_stack: convert generic dump

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Date:   Wed, 7 Mar 2018 11:21:27 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Petr Mladek <pmladek@...e.com>, Tejun Heo <tj@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Dave Young <dyoung@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Greentime Hu <green.hu@...il.com>,
        Vincent Chen <deanbo422@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        adi-buildroot-devel@...ts.sourceforge.net,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH] dump_stack: convert generic dump_stack into a weak symbol

Hello Arnd,

On (03/06/18 14:27), Arnd Bergmann wrote:
[..]
> As we are now removing blackfin, based on the latest discussion, this
> part should no longer be necessary.

When is this going to happen? 4.17?

[..]
> nds32 currently only exists in linux-next, not in the mainline kernel.
> If it's the only architecture that does something different from everyone
> else, I think we should change nds32.
> 
> I looked at the nds32 show_stack() implementation now and it
> seems to me that it is completely unnecessary, as the implementation
> from lib/dump_stack.c does basically the same thing (by calling
> show_stack(NULL, NULL)).

Interesting point. I'll leave it to nds32 maintainers.
OTOH blackfin is still in linux-next, so I assume we need
that __weak dump_stack() for the time being.

[..]
> > +asmlinkage __weak __visible void dump_stack(void)
> >  {
> >         __dump_stack();
> >  }
> 
> Weak symbols are generally discouraged in the kernel. We have
> them in a couple of places, but I find them rather confusing as they
> make it harder to figure out what is actually going on.

Honestly, I kind of find __weak less confusing than EXPORT_SYMBOL(dump_stack)
in 3 different places. __weak hints that the symbol likely will be overridden
somewhere, while EXPORT_SYMBOL() does not (at least not to me). Dunno.

	-ss