netdev - Re: skb_splice_bits() and large chunks in pipe (was Re: xfs_file_splice_read: possible circular locking dependency detected

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Message-ID: <CA+55aFx3L3WbjC3vwpj=LDWEUsSYrUHONOjpRYs4h0BHEC57Ew@mail.gmail.com>
Date:   Sun, 18 Sep 2016 17:18:34 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Jens Axboe <axboe@...nel.dk>, Nick Piggin <npiggin@...il.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: skb_splice_bits() and large chunks in pipe (was Re:
 xfs_file_splice_read: possible circular locking dependency detected

On Sun, Sep 18, 2016 at 3:31 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
>
> What worries me is iov_iter_get_pages() and friends.

So honestly, if it worries you, I'm not going to complain at all if
you decide that you'd rather translate the pipe_buffer[] array into a
kvec by always splitting at page boundaries.

Even with large packets in networking, it's not going t be a huge
deal. And maybe we *should* make it a rule that a "kvec" is always
composed of individual entries that fit entirely within a page.

In this code, being safe rather than clever would be a welcome and
surprising change, I guess.

             Linus