From: "Colin Walters" <walters@verbum.org>
To: "James Bottomley" <James.Bottomley@HansenPartnership.com>,
"Matthew Wilcox" <willy@infradead.org>,
"Dave Chinner" <david@fromorbit.com>
Cc: "Roman Gushchin" <roman.gushchin@linux.dev>,
"Stephen Brennan" <stephen.s.brennan@oracle.com>,
lsf-pc@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org,
"Gautham Ananthakrishna" <gautham.ananthakrishna@oracle.com>,
khlebnikov@yandex-team.ru
Subject: Re: [LSF/MM TOPIC] Better handling of negative dentries
Date: Tue, 22 Mar 2022 16:17:16 -0400 [thread overview]
Message-ID: <42d92c6f-28f2-459b-bc2a-13dd655dd4ae@www.fastmail.com> (raw)
In-Reply-To: <a8f6ea9ec9b8f4d9b48e97fe1236f80b62b76dc1.camel@HansenPartnership.com>
On Tue, Mar 22, 2022, at 3:19 PM, James Bottomley wrote:
>
> Well, firstly what is the exact problem? People maliciously looking up
> nonexistent files
Maybe most people have seen it, but for those who haven't:
https://bugzilla.redhat.com/show_bug.cgi?id=1571183
was definitely one of those things that just makes one recoil in horror.
TL;DR NSS used to have code that tried to detect "is this a network filesystem"
by timing `stat()` calls to nonexistent paths, and this massively boated
the negative dentry cache and caused all sorts of performance problems.
It was particularly confusing because this would just happen as a side effect of e.g. executing `curl https://somewebsite`.
That code wasn't *intentionally* malicious but...
next prev parent reply other threads:[~2022-03-22 20:17 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-15 19:55 [LSF/MM TOPIC] Better handling of negative dentries Matthew Wilcox
2022-03-15 20:56 ` Roman Gushchin
2022-03-16 2:07 ` Gao Xiang
2022-03-16 2:52 ` Dave Chinner
2022-03-16 3:08 ` Gao Xiang
2022-03-22 15:08 ` Matthew Wilcox
2022-03-22 19:19 ` James Bottomley
2022-03-22 20:17 ` Colin Walters [this message]
2022-03-22 20:27 ` James Bottomley
2022-03-22 20:37 ` Matthew Wilcox
2022-03-22 21:08 ` Stephen Brennan
2022-03-29 15:24 ` James Bottomley
2022-03-31 19:27 ` Stephen Brennan
2022-04-01 15:45 ` James Bottomley
2022-03-22 22:21 ` Dave Chinner
2022-03-22 20:41 ` Matthew Wilcox
2022-03-22 21:19 ` Roman Gushchin
2022-03-22 22:29 ` Dave Chinner
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