linux-kernel - Re: [PATCH 1/2] mm: add GFP mask param to strndup

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Date:   Sun, 16 Aug 2020 19:10:15 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Pascal Bouchareine <kalou@....net>, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org, netdev@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/2] mm: add GFP mask param to strndup_user

On Sat, Aug 15, 2020 at 11:42:10PM +0100, Al Viro wrote:
> On Sat, Aug 15, 2020 at 11:23:43AM -0700, Pascal Bouchareine wrote:
> > Let caller specify allocation.
> > Preserve existing calls with GFP_USER.
> 
> Bloody bad idea, unless you slap a BUG_ON(flags & GFP_ATOMIC) on it,
> to make sure nobody tries _that_.  Note that copying from userland
> is an inherently blocking operation, and this interface invites
> just that.
> 
> What do you need that flag for, anyway?

You need it for kmem accounting.