All of lore.kernel.org
 help / color / mirror / Atom feed
From: "Christian König" <ckoenig.leichtzumerken@gmail.com>
To: Jan Harkes <jaharkes@cs.cmu.edu>
Cc: linux-kernel@vger.kernel.org, linux-unionfs@vger.kernel.org,
	dri-devel@lists.freedesktop.org, coda@cs.cmu.edu,
	miklos@szeredi.hu, akpm@linux-foundation.org, jgg@ziepe.ca
Subject: Re: [PATCH 1/2] coda: fix reference counting in coda_file_mmap error path
Date: Fri, 23 Apr 2021 10:10:26 +0200	[thread overview]
Message-ID: <1dce6311-c708-19a8-a9cb-489602d6e930@gmail.com> (raw)
In-Reply-To: <20210422135103.hif4a5znhzt4pc6f@cs.cmu.edu>

Am 22.04.21 um 15:51 schrieb Jan Harkes:
> On Thu, Apr 22, 2021 at 02:39:41PM +0200, Christian König wrote:
>> Am 22.04.21 um 14:27 schrieb Jan Harkes:
>>> Looks good to me.
>>>
>>> I'm also maintaining an out of tree coda module build that people sometimes use, which has workarounds for differences between the various kernel versions.
>>>
>>> Do you have a reference to the corresponding mmap_region change? If it is merged already I'll probably be able to find it. Is this mmap_region change expected to be backported to any lts kernels?
>> That is the following upstream commit in Linus tree:
>>
>> commit 1527f926fd04490f648c42f42b45218a04754f87
>> Author: Christian König <christian.koenig@amd.com>
>> Date:   Fri Oct 9 15:08:55 2020 +0200
>>
>>      mm: mmap: fix fput in error path v2
>>
>> But I don't think we should backport that.
>>
>> And sorry for the noise. We had so many places which expected different
>> behavior that I didn't noticed that two occasions in the fs code actually
>> rely on the current behavior.
>>
>> For your out of tree module you could make the code version independent by
>> setting the vma back to the original file in case of an error. That should
>> work with both behaviors in mmap_region.
> Awesome, I'll give that a try, it may very well be a cleaner solution
> either way.
>
> And thank you for following up after your original patch and finding
> the filesystems that mess around with those mappings. I'm sure it would
> have taken me a while to figure out why file refcounts would go weird
> for some people, especially because this only happens in the error path.

Kudos goes to Miklos for figured out why the refcount for overlayfs was 
suddenly wrong.

And please also see the follow up commit:

commit 295992fb815e791d14b18ef7cdbbaf1a76211a31 (able/vma_file)
Author: Christian König <christian.koenig@amd.com>
Date:   Mon Sep 14 15:09:33 2020 +0200

     mm: introduce vma_set_file function v5

It adds a new vma_set_file() function which implements the necessary 
refcount dance for changing the vma file in a clean manner.

Thanks,
Christian.

>
> Jan
>


WARNING: multiple messages have this Message-ID (diff)
From: "Christian König" <ckoenig.leichtzumerken@gmail.com>
To: Jan Harkes <jaharkes@cs.cmu.edu>
Cc: jgg@ziepe.ca, miklos@szeredi.hu, linux-kernel@vger.kernel.org,
	dri-devel@lists.freedesktop.org, linux-unionfs@vger.kernel.org,
	coda@cs.cmu.edu, akpm@linux-foundation.org
Subject: Re: [PATCH 1/2] coda: fix reference counting in coda_file_mmap error path
Date: Fri, 23 Apr 2021 10:10:26 +0200	[thread overview]
Message-ID: <1dce6311-c708-19a8-a9cb-489602d6e930@gmail.com> (raw)
In-Reply-To: <20210422135103.hif4a5znhzt4pc6f@cs.cmu.edu>

Am 22.04.21 um 15:51 schrieb Jan Harkes:
> On Thu, Apr 22, 2021 at 02:39:41PM +0200, Christian König wrote:
>> Am 22.04.21 um 14:27 schrieb Jan Harkes:
>>> Looks good to me.
>>>
>>> I'm also maintaining an out of tree coda module build that people sometimes use, which has workarounds for differences between the various kernel versions.
>>>
>>> Do you have a reference to the corresponding mmap_region change? If it is merged already I'll probably be able to find it. Is this mmap_region change expected to be backported to any lts kernels?
>> That is the following upstream commit in Linus tree:
>>
>> commit 1527f926fd04490f648c42f42b45218a04754f87
>> Author: Christian König <christian.koenig@amd.com>
>> Date:   Fri Oct 9 15:08:55 2020 +0200
>>
>>      mm: mmap: fix fput in error path v2
>>
>> But I don't think we should backport that.
>>
>> And sorry for the noise. We had so many places which expected different
>> behavior that I didn't noticed that two occasions in the fs code actually
>> rely on the current behavior.
>>
>> For your out of tree module you could make the code version independent by
>> setting the vma back to the original file in case of an error. That should
>> work with both behaviors in mmap_region.
> Awesome, I'll give that a try, it may very well be a cleaner solution
> either way.
>
> And thank you for following up after your original patch and finding
> the filesystems that mess around with those mappings. I'm sure it would
> have taken me a while to figure out why file refcounts would go weird
> for some people, especially because this only happens in the error path.

Kudos goes to Miklos for figured out why the refcount for overlayfs was 
suddenly wrong.

And please also see the follow up commit:

commit 295992fb815e791d14b18ef7cdbbaf1a76211a31 (able/vma_file)
Author: Christian König <christian.koenig@amd.com>
Date:   Mon Sep 14 15:09:33 2020 +0200

     mm: introduce vma_set_file function v5

It adds a new vma_set_file() function which implements the necessary 
refcount dance for changing the vma file in a clean manner.

Thanks,
Christian.

>
> Jan
>

_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

  reply	other threads:[~2021-04-23  8:10 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-21 13:20 [PATCH 1/2] coda: fix reference counting in coda_file_mmap error path Christian König
2021-04-21 13:20 ` Christian König
2021-04-21 13:20 ` [PATCH 2/2] ovl: fix reference counting in ovl_mmap " Christian König
2021-04-21 13:20   ` Christian König
2021-04-22  8:13   ` Daniel Vetter
2021-04-22  8:13     ` Daniel Vetter
2021-04-22  8:11 ` [PATCH 1/2] coda: fix reference counting in coda_file_mmap " Daniel Vetter
2021-04-22  8:11   ` Daniel Vetter
2021-04-22 12:27 ` Jan Harkes
2021-04-22 12:27   ` Jan Harkes
2021-04-22 12:39   ` Christian König
2021-04-22 12:39     ` Christian König
2021-04-22 13:51     ` Jan Harkes
2021-04-22 13:51       ` Jan Harkes
2021-04-23  8:10       ` Christian König [this message]
2021-04-23  8:10         ` Christian König

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=1dce6311-c708-19a8-a9cb-489602d6e930@gmail.com \
    --to=ckoenig.leichtzumerken@gmail.com \
    --cc=akpm@linux-foundation.org \
    --cc=coda@cs.cmu.edu \
    --cc=dri-devel@lists.freedesktop.org \
    --cc=jaharkes@cs.cmu.edu \
    --cc=jgg@ziepe.ca \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-unionfs@vger.kernel.org \
    --cc=miklos@szeredi.hu \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.