From: Alexander Lochmann <alexander.lochmann@tu-dortmund.de>
To: "Theodore Ts'o" <tytso@mit.edu>
Cc: Horst Schirmeier <horst.schirmeier@tu-dortmund.de>,
Jan Kara <jack@suse.cz>, Jan Kara <jack@suse.com>,
linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC] inode.i_opflags - Usage of two different locking schemes
Date: Mon, 8 Mar 2021 15:05:33 +0100 [thread overview]
Message-ID: <0f387f5b-a516-af45-856d-f38d1adfadf5@tu-dortmund.de> (raw)
In-Reply-To: <YEJWiXaZ+9H+2nBx@mit.edu>
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On 05.03.21 17:04, Theodore Ts'o wrote:
> On Fri, Mar 05, 2021 at 04:35:47PM +0100, Alexander Lochmann wrote:
>>
>>
>> On 05.03.21 16:18, Theodore Ts'o wrote:
>>> 1) I don't see where i_opflags is being read in ipc/mqueue.c at all,
>>> either with or without i_rwsem.
>>>
>> It is read in fs/dcache.c
>
> So why is this unique to the mqueue inode then? It might be helpful
> to have explicit call stacks in the e-mail, in text form, when you
> resend to LKML.
It is unique to mqeue inode, because the control flow goes through
ipc/mqueue.c where almost always the i_rwsem is taken.
Hence, we see more memory accesses to an mqueue inode with the i_rwsem.
The i_lock is less often hold compared to the i_rwsem.
We conclude the i_rwsem is needed. So it might not be a contradiction at
all. It rather could be a flaw in our approach. :-/
Besides from our current discussion:
Does the i_lock protect i_opflags for both reading and writing?
Cheers,
Alex
>
> That's because the HTML file is ***huge*** (1.7Meg), and I'm having
> trouble with my browser properly rendering it. In any case, the html
> claims to be showing the counter examples and I'm still stuck on the
> *example*?
>
> Cheers,
>
> - Ted
>
--
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next prev parent reply other threads:[~2021-03-08 14:06 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <f63dd495-defb-adc4-aa91-6aacd7f441c7@tu-dortmund.de>
2021-03-05 13:10 ` [RFC] inode.i_opflags - Usage of two different locking schemes Alexander Lochmann
2021-03-05 15:18 ` Theodore Ts'o
2021-03-05 15:35 ` Alexander Lochmann
2021-03-05 16:04 ` Theodore Ts'o
2021-03-08 14:05 ` Alexander Lochmann [this message]
2021-03-16 17:14 ` Jan Kara
2021-03-26 16:37 ` Alexander Lochmann
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