linux-kernel - Re: [PATCH v2 2/2] livepatch: Use static buffer for debugging messages under rq lock

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Message-ID: <20190507115029.54qxbsd4vsouwvjo@pathway.suse.cz>
Date:   Tue, 7 May 2019 13:50:29 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Jiri Kosina <jikos@...nel.org>, Miroslav Benes <mbenes@...e.cz>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] livepatch: Use static buffer for debugging
 messages under rq lock

On Mon 2019-05-06 19:43:19, Josh Poimboeuf wrote:
> On Tue, Apr 30, 2019 at 11:10:49AM +0200, Petr Mladek wrote:
> > klp_try_switch_task() is called under klp_mutex. The buffer for
> > debugging messages might be static.
> 
> The patch description is missing a "why" (presumably to reduce stack
> usage).

Exactly. I thought that it was obvious. But I am infected by printk
code where line buffers are 1k and nobody wants them on the stack.

128bytes in klp_try_switch_task() context are acceptable but
it is still rather big buffer.

OK, what about the following commit message?

"klp_try_switch_task() is called under klp_mutex. The buffer for
debugging messages might be static to reduce stack usage."

Best Regards,
Petr