linux-kernel - Re: Kernel crash in free_pipe

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Date:   Mon, 30 Oct 2017 15:14:15 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: Kernel crash in free_pipe_info()

On Mon, Oct 30, 2017 at 1:58 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
>
> We got more than a dozen of kernel crashes at free_pipe_info() on our
> 4.1 kernel, they are all very similar to this one (with slightly
> different faulty addresses):

Were it not for the pointer to the much more recent powerpc version at

    https://www.spinics.net/lists/kernel/msg2616441.html

that you referenced, I'd be inclined to ignore this as much too old.
Al fixed a number of issues with splice() some time ago.

And honestly, splice() is pretty much the only thing that I can think
of that can trigger issues wrt the pipe_inode_info structure.

But as you say, we've had subtle races just due to the named pipes:

> Although it is too early to blame your commit b0d8d2292160 ("vfs: fix
> subtle use-after-free of pipe_inode_info"), it is probably related.

I do hate the games we play with the stupid pipe_inode_info. The way
we have locking in the inode, instead of in the pipe_inode_info
itself.

There are hysterical raisins for that, and due to names piped we have
to keep the reference to the pipe_inode_info in the inode, but it's
still very very annoying.

Al, do you see anything?

Cong, do you have any way to trigger these? Is there any pattern to
when they happen or what is going on when they do?

           Linus