Re: [PATCH 3/3] btrfs: Avoid live-lock in search_ioctl() on hardware with sub-page faults

From: Catalin Marinas <catalin.marinas@arm.com>
To: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Josef Bacik <josef@toxicpanda.com>,
	David Sterba <dsterba@suse.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Andrew Morton <akpm@linux-foundation.org>,
	Will Deacon <will@kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	linux-btrfs <linux-btrfs@vger.kernel.org>
Subject: Re: [PATCH 3/3] btrfs: Avoid live-lock in search_ioctl() on hardware with sub-page faults
Date: Mon, 29 Nov 2021 13:52:12 +0000	[thread overview]
Message-ID: <YaTbDJS5MtvIm9aS@arm.com> (raw)
In-Reply-To: <CAHc6FU7BSL58GVkOh=nsNQczRKG3P+Ty044zs7PjKPik4vzz=Q@mail.gmail.com>

On Sat, Nov 27, 2021 at 07:05:39PM +0100, Andreas Gruenbacher wrote:
> Maybe you want to add this though:
> 
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -2202,3 +2202,3 @@ static noinline int search_ioctl(struct inode *inode,
>         unsigned long sk_offset = 0;
> -       char __user *fault_in_addr;
> +       char __user *fault_in_addr, *end;
> 
> @@ -2230,6 +2230,6 @@ static noinline int search_ioctl(struct inode *inode,
>         fault_in_addr = ubuf;
> +       end = ubuf + *buf_size;
>         while (1) {
>                 ret = -EFAULT;
> -               if (fault_in_writeable(fault_in_addr,
> -                                      *buf_size - (fault_in_addr - ubuf)))
> +               if (fault_in_writeable(fault_in_addr, end - fault_in_addr))
>                         break;

It looks like *buf_size is updated inside copy_to_sk(), so I'll move the
end update inside the loop.

-- 
Catalin