From: Linus Torvalds <torvalds@linux-foundation.org>
To: mnipxh <mnipxh@gmail.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
Yanmin Zhang <yanmin_zhang@linux.intel.com>,
shuox.liu@intel.com
Subject: Re: [PATCH] fs/buffer.c: grow_buffers: fix the uncorrect check
Date: Sat, 31 May 2014 12:39:34 -0700 [thread overview]
Message-ID: <CA+55aFzfrGYCeUgXkeVowfJY+CL6MFPo7LpWSGiZvKhGA_qroQ@mail.gmail.com> (raw)
In-Reply-To: <538A1B75.5030107@gmail.com>
On Sat, May 31, 2014 at 11:12 AM, mnipxh <mnipxh@gmail.com> 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
prev parent reply other threads:[~2014-05-31 19:39 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-31 18:12 [PATCH] fs/buffer.c: grow_buffers: fix the uncorrect check mnipxh
2014-05-31 19:39 ` Linus Torvalds [this message]
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