linux-kernel - Re: [PATCH 3/3] btrfs: Avoid live-lock in search

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Message-ID: <YaTbDJS5MtvIm9aS@arm.com>
Date:   Mon, 29 Nov 2021 13:52:12 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Andreas Gruenbacher <agruenba@...hat.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Will Deacon <will@...nel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-btrfs <linux-btrfs@...r.kernel.org>
Subject: Re: [PATCH 3/3] btrfs: Avoid live-lock in search_ioctl() on hardware
 with sub-page faults

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