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([2620:10d:c091:480::1:fe9c]) by smtp.gmail.com with ESMTPSA id k31sm7048362qtd.60.2020.08.13.10.08.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 13 Aug 2020 10:08:51 -0700 (PDT) Subject: Re: [PATCH] proc: use vmalloc for our kernel buffer To: David Laight , "hch@lst.de" , "viro@ZenIV.linux.org.uk" , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "kernel-team@fb.com" References: <20200813145305.805730-1-josef@toxicpanda.com> <714c8baabe1a4d0191f8cdaf6e28a32d@AcuMS.aculab.com> From: Josef Bacik Message-ID: <72ea0ff5-4706-d2e9-c2cf-c8827e576399@toxicpanda.com> Date: Thu, 13 Aug 2020 13:08:49 -0400 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <714c8baabe1a4d0191f8cdaf6e28a32d@AcuMS.aculab.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/13/20 12:19 PM, David Laight wrote: > 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 > /* don't even try if the size is too large */ error = -ENOMEM; if (count >= KMALLOC_MAX_SIZE) goto out; is above this code, thanks, Josef