Re: 9p: fscache duplicate cookie

From: Luis Henriques <lhenriques@suse.de>
To: David Howells <dhowells@redhat.com>
Cc: Eric Van Hensbergen <ericvh@gmail.com>,
	Latchesar Ionkov <lucho@ionkov.net>,
	Dominique Martinet <asmadeus@codewreck.org>,
	linux-fsdevel@vger.kernel.org,
	v9fs-developer@lists.sourceforge.net
Subject: Re: 9p: fscache duplicate cookie
Date: Wed, 12 May 2021 12:58:58 +0100	[thread overview]
Message-ID: <87fsysyxh9.fsf@suse.de> (raw)
In-Reply-To: <2882181.1620817453@warthog.procyon.org.uk> (David Howells's message of "Wed, 12 May 2021 12:04:13 +0100")

David Howells <dhowells@redhat.com> writes:

> Luis Henriques <lhenriques@suse.de> wrote:
>
>> [ I wonder why the timestamps don't match between the traces and the
>>   kernel log... ]
>
> I've seen that.  I wonder if the timestamping of printk lines is delayed by
> the serial driver outputting things.
>
>> So, can we infer from this trace that an evict could actually be on-going
>> but the old cookie wasn't relinquished yet and hence the collision?
>
> It might be illuminating if you can make it print a traceline at the beginning
> of v9fs_evict_inode() and in v9fs_drop_inode().  Print the cookie pointer in
> both.

Ok, here's what I'm getting:

...
<...>-20575   [002] ...1    67.519214: fscache_acquire: c=0000000097476aaa p=000000003080d900 pu=50 pc=49 pf=22 n=9p.inod
<...>-20585   [003] ...2    67.535091: 9p_fscache_cookie: v9fs_drop_inode cookie: 00000000cd0099b3
<...>-20585   [003] ...1    67.535093: 9p_fscache_cookie: v9fs_evict_inode cookie: 00000000cd0099b3
<...>-20585   [003] ...1    67.535115: fscache_relinquish: c=00000000cd0099b3 u=1 p=000000003080d900 Nc=0 Na=1 f=26 r=0
<...>-20585   [003] ...1    67.535118: fscache_cookie: PUT rlq c=00000000cd0099b3 u=0 p=000000003080d900 Nc=0 Na=0 f=16
<...>-20585   [003] ...1    67.535120: fscache_cookie: PUT prn c=000000003080d900 u=49 p=0000000042542ee5 Nc=48 Na=1 f=22
<...>-20591   [000] ...2    67.538644: fscache_cookie: GET prn c=000000003080d900 u=50 p=0000000042542ee5 Nc=48 Na=1 f=22
<...>-20591   [000] ...1    67.538645: fscache_acquire: c=0000000011fa06b1 p=000000003080d900 pu=50 pc=49 pf=22 n=9p.inod
<...>-20599   [003] .N.2    67.542180: 9p_fscache_cookie: v9fs_drop_inode cookie: 0000000097476aaa
<...>-20599   [003] .N.1    67.542181: 9p_fscache_cookie: v9fs_evict_inode cookie: 0000000097476aaa
<...>-20591   [000] ...2    67.542980: fscache_cookie: *COLLISION* c=0000000097476aaa u=1 p=000000003080d900 Nc=0 Na=1 f=26
<...>-20599   [003] ...1    67.543098: fscache_relinquish: c=0000000097476aaa u=1 p=000000003080d900 Nc=0 Na=1 f=26 r=0
<...>-20599   [003] ...1    67.543100: fscache_cookie: PUT rlq c=0000000097476aaa u=0 p=000000003080d900 Nc=0 Na=0 f=16

(Note that I'm only tracing v9fs_{drop,evict}_inode if we have a cookie
for the inode; there are a bunch of drop/evict calls where the cookie is
NULL.)

So, this is... annoying, I guess.

Cheers,
-- 
Luis