Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   David Laight <David.Laight@ACULAB.COM>
To:     'Josef Bacik' <josef@toxicpanda.com>, "hch@lst.de" <hch@lst.de>,
        "viro@ZenIV.linux.org.uk" <viro@ZenIV.linux.org.uk>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kernel-team@fb.com" <kernel-team@fb.com>
Subject: RE: [PATCH] proc: use vmalloc for our kernel buffer
Thread-Topic: [PATCH] proc: use vmalloc for our kernel buffer
Thread-Index: AQHWcYF4YUlfHEUFrEai+1gWcwt4Jak2N4WQ
Date:   Thu, 13 Aug 2020 16:19:27 +0000
Message-ID: <714c8baabe1a4d0191f8cdaf6e28a32d@AcuMS.aculab.com>
References: <20200813145305.805730-1-josef@toxicpanda.com>
In-Reply-To: <20200813145305.805730-1-josef@toxicpanda.com>
Accept-Language: en-GB, en-US
Content-Language: en-US
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8BIT
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

From: Josef Bacik
> Sent: 13 August 2020 15:53
> 
>   sysctl: pass kernel pointers to ->proc_handler
> 
> we have been pre-allocating a buffer to copy the data from the proc
> handlers into, and then copying that to userspace.  The problem is this
> just blind kmalloc()'s the buffer size passed in from the read, which in
> the case of our 'cat' binary was 64kib.  Order-4 allocations are not
> awesome, and since we can potentially allocate up to our maximum order,
> use vmalloc for these buffers.

What happens if I run 'dd bs=16M ...' ?

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)