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Date: Thu, 20 Feb 2020 17:37:44 -0600
From: ebiederm@...ssion.com (Eric W. Biederman)
To: Al Viro <viro@...iv.linux.org.uk>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>, LKML <linux-kernel@...r.kernel.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, Linux API <linux-api@...r.kernel.org>, Linux FS Devel <linux-fsdevel@...r.kernel.org>, Linux Security Module <linux-security-module@...r.kernel.org>, Akinobu Mita <akinobu.mita@...il.com>, Alexey Dobriyan <adobriyan@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, Andy Lutomirski <luto@...nel.org>, Daniel Micay <danielmicay@...il.com>, Djalal Harouni <tixxdz@...il.com>, "Dmitry V . Levin" <ldv@...linux.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Ingo Molnar <mingo@...nel.org>, "J . Bruce Fields" <bfields@...ldses.org>, Jeff Layton <jlayton@...chiereds.net>, Jonathan Corbet <corbet@....net>, Kees Cook <keescook@...omium.org>, Oleg Nesterov <oleg@...hat.com>, Solar Designer <solar@...nwall.com>
Subject: Re: [PATCH 0/7] proc: Dentry flushing without proc_mnt
Al Viro <viro@...iv.linux.org.uk> writes:
> On Thu, Feb 20, 2020 at 03:02:22PM -0800, Linus Torvalds wrote:
>> On Thu, Feb 20, 2020 at 12:48 PM Eric W. Biederman
>> <ebiederm@...ssion.com> wrote:
>> >
>> > Linus, does this approach look like something you can stand?
>>
>> A couple of worries, although one of them seem to have already been
>> resolved by Al.
>>
>> I think the real gatekeeper should be Al in general. But other than
>> the small comments I had, I think this might work just fine.
>>
>> Al?
>
> I'll need to finish RTFS there; I have initially misread that patch,
> actually - Eric _is_ using that thing both for those directories
> and for sysctl inodes. And the prototype for that machinery (the
> one he'd pulled from proc_sysctl.c) is playing with pinning superblocks
> way too much; for per-pid directories that's not an issue, but
> for sysctl table removal you are very likely to hit a bunch of
> evictees on the same superblock...
I saw that was possible. If the broad strokes look correct I don't have
a problem at all with optimizing for the case where many of the entries
are for inodes on the same superblock. I just had enough other details
on my mind I was afraid if I got a little more clever I would have
introduced a typo somewhere.
I wish I could limit the sysctl parts to just directories, but
unfortunately the sysctl tables don't always give a guarantee that a
directory is what will be removed. But sysctls do have one name per
inode invarant like fat. There is no way to express a sysctl
table that doesn't have that invariant.
As for d_find_alias/d_invalidate.
Just for completeness I wanted to write a loop:
while (dentry = d_find_alias(inode)) {
d_invalidate(dentry);
dput(dentry);
}
Unfortunately that breaks on directories, because for directories
d_find_alias turns into d_find_any_alias, and continues to return aliases
even when they are unhashed.
It might be nice to write a cousin of d_prune_aliases call
it d_invalidate_aliases that just does that loop the correct way
in dcache.c
Eric
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