linux-kernel - Re: [PATCH] Convert filldir[64]() from __put_user() to unsafe_put

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Date:   Mon, 7 Oct 2019 21:14:51 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] Convert filldir[64]() from __put_user() to unsafe_put_user()

On Mon, Oct 7, 2019 at 9:09 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> Try the attached patch, and then count the number of "rorx"
> instructions in the kernel. Hint: not many. On my personal config,
> this triggers 15 times in the whole kernel build (not counting
> modules).

So here's a serious patch that doesn't just mark things for counting -
it just removes the cases entirely.

Doesn't this look nice:

  2 files changed, 2 insertions(+), 133 deletions(-)

and it is one less thing to worry about when doing further cleanup.

Seriously, if any of those __copy_{to,from}_user() constant cases were
a big deal, we can turn them into get_user/put_user calls. But only
after they show up as an actual performance issue.

            Linus

View attachment "patch.diff" of type "text/x-patch" (4900 bytes)