Re: [PATCH 1/1] Revert "iomap: fall back to buffered writes for invalidation failures"

Matthew Wilcox
2022-02-11T14:37:23Z

On Thu, Feb 10, 2022 at 10:15:52AM +0000, Lee Jones wrote:
> On Wed, 09 Feb 2022, Darrick J. Wong wrote:
>
> > On Wed, Feb 09, 2022 at 08:52:43AM +0000, Lee Jones wrote:
> > > This reverts commit 60263d5889e6dc5987dc51b801be4955ff2e4aa7.
> > >
> > > Reverting since this commit opens a potential avenue for abuse.
> >
> > What kind of abuse? Did you conclude there's an avenue solely because
> > some combination of userspace rigging produced a BUG warning? Or is
> > this a real problem that someone found?
>
> Genuine question: Is the ability for userspace to crash the kernel
> not enough to cause concern? I would have thought that we'd want to
> prevent this.

The kernel doesn't crash. It's a BUG(). That means it kills the
task which caused the BUG(). If you've specified that the kernel should
crash on seeing a BUG(), well, you made that decision, and you get to
live with the consequences.

> The link provided doesn't contain any further analysis. Only the
> reproducer and kernel configuration used, which are both too large to
> enter into a Git commit.

But not too large to put in an email. Which you should have sent to
begin with, not a stupid reversion commit.

> > OH WAIT, you're running this on the Android 5.10 kernel, aren't you?
> > The BUG report came from page_buffers failing to find any buffer heads
> > attached to the page.
> > https://android.googlesource.com/kernel/common/+/refs/heads/android12-5.10-2022-02/fs/ext4/inode.c#2647
>
> Yes, the H/W I have to prototype these on is a phone and the report
> that came in was specifically built against the aforementioned
> kernel.
>
> > Yeah, don't care.
>
> "There is nothing to worry about, as it's intended behaviour"?

No. You've come in like a fucking meteorite full of arrogance and
ignorance. Nobody's reacting well to you right now. Start again,
write a good bug report in a new thread.