From mboxrd@z Thu Jan 1 00:00:00 1970 From: Linus Torvalds Subject: Re: [PATCH] fs/buffer.c: grow_buffers: fix the uncorrect check Date: Sat, 31 May 2014 12:39:34 -0700 Message-ID: References: <538A1B75.5030107@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: Linux Kernel Mailing List , linux-fsdevel , Al Viro , Andrew Morton , Yanmin Zhang , shuox.liu@intel.com To: mnipxh Return-path: In-Reply-To: <538A1B75.5030107@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Sat, May 31, 2014 at 11:12 AM, mnipxh wrote: > When pgoff_t index is 32bit, sector_t block is 64bit, need check if block number is too big. > If block is bigger than (4Gb * PAGE_SIZE), index becomes a wrong value. > Commit e5657933863f43cc6bb76a54d659303dafaa9e58 wants to do this. But it gives an uncorrect check. > I think block != index << sizebits is correct. And it can detect such issue above. I don't understand why you think the current check is incorrect. It is testing that the calculation hasn't overflowed. It is correct. It *should* use the same calculation, to (a) make it more obvious that it's double-checking the earlier calculation in a different type, and (b) to make it easier for the compiler to optimize it away if sector_t and pgoff_t are the same size. So the current code is correct, afaik. Note that "index" is "pgoff_t", but "block >> sizebits" is "sector_t". Linus