linux-kernel - Re: [PATCH next] vt: fix a warning when kmalloc alloc large memory

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Message-ID: <nycvar.YSQ.7.76.2003272232340.2671@knanqh.ubzr>
Date:   Fri, 27 Mar 2020 22:55:14 -0400 (EDT)
From:   Nicolas Pitre <nico@...xnic.net>
To:     Chen Wandun <chenwandun@...wei.com>
cc:     jslaby@...e.com, gregkh@...uxfoundation.org,
        daniel.vetter@...ll.ch, sam@...nborg.org, b.zolnierkie@...sung.com,
        lukas@...ner.de, ghalat@...hat.com, kilobyte@...band.pl,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH next] vt: fix a warning when kmalloc alloc large memory

On Sat, 28 Mar 2020, Chen Wandun wrote:

> If the memory size that use kmalloc() to allocate exceed MAX_ORDER pages,
> it will hit the WARN_ON_ONCE(!(gfp_mask & __GFP_NOWARN)), so add memory
> allocation flag __GFP_NOWARN to silence a warning, othervise, it will
> cause panic if panic_on_warn is enable.

Wow! How do you manage that? You need something like a 1024x1024 text 
screen to get such a big memory allocation.

Still, GFP_NOWARN is not a proper fix. This kmalloc() should rather be 
replaced by vmalloc(), and corresponding kfree() should then be vfree(). 
There is no need for this allocation to be physically contiguous.

Nicolas