From: Bruce Fields <bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org>
To: Jeff Layton <jlayton-vpEMnDpepFuMZCB2o+C8xQ@public.gmane.org>
Cc: David Windsor <dwindsor-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
kernel-hardening-ZwoEplunGu1jrUoiu81ncdBPR1lH4CV8@public.gmane.org,
Kees Cook <keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>,
"Reshetova,
Elena" <elena.reshetova-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Subject: Re: [RFC][PATCH] nfsd: add +1 to reference counting scheme for struct nfsd4_session
Date: Sat, 11 Feb 2017 20:15:21 -0500 [thread overview]
Message-ID: <20170212011521.GD2768@fieldses.org> (raw)
In-Reply-To: <1486816302.4233.29.camel-vpEMnDpepFuMZCB2o+C8xQ@public.gmane.org>
On Sat, Feb 11, 2017 at 07:31:42AM -0500, Jeff Layton wrote:
> The basic idea here is that nfsv4 sessions have a "resting state" of 0.
> We want to keep them around, but if they go "dead" then we we'll tear
> them down if they aren't actively in use at the time. So, we still free
> the thing when the refcount goes to zero, but we have an extra condition
> before we free it on the put -- that the session is also "dead" (meaning
> that the client asked us to destroy it).
>
> Your patch doesn't look like it'll break anything, but I personally find
> it harder to follow that way. The freeable reference state will be 1
> instead of the normal 0.
Alas, I don't have any examples in mind, but doesn't this pattern happen
all over?
You have objects that live in some data structure. They're freed only
when they're removed from the data structure. You want removal to fail
whenever they're in use.
So it's natural to use an atomic counter to track the number of external
users and some other lock to serialize lookup and destruction.
--b.
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WARNING: multiple messages have this Message-ID (diff)
From: Bruce Fields <bfields@fieldses.org>
To: Jeff Layton <jlayton@poochiereds.net>
Cc: David Windsor <dwindsor@gmail.com>,
linux-nfs@vger.kernel.org, netdev@vger.kernel.org,
kernel-hardening@lists.openwall.com,
Kees Cook <keescook@chromium.org>,
"Reshetova, Elena" <elena.reshetova@intel.com>
Subject: Re: [RFC][PATCH] nfsd: add +1 to reference counting scheme for struct nfsd4_session
Date: Sat, 11 Feb 2017 20:15:21 -0500 [thread overview]
Message-ID: <20170212011521.GD2768@fieldses.org> (raw)
In-Reply-To: <1486816302.4233.29.camel@poochiereds.net>
On Sat, Feb 11, 2017 at 07:31:42AM -0500, Jeff Layton wrote:
> The basic idea here is that nfsv4 sessions have a "resting state" of 0.
> We want to keep them around, but if they go "dead" then we we'll tear
> them down if they aren't actively in use at the time. So, we still free
> the thing when the refcount goes to zero, but we have an extra condition
> before we free it on the put -- that the session is also "dead" (meaning
> that the client asked us to destroy it).
>
> Your patch doesn't look like it'll break anything, but I personally find
> it harder to follow that way. The freeable reference state will be 1
> instead of the normal 0.
Alas, I don't have any examples in mind, but doesn't this pattern happen
all over?
You have objects that live in some data structure. They're freed only
when they're removed from the data structure. You want removal to fail
whenever they're in use.
So it's natural to use an atomic counter to track the number of external
users and some other lock to serialize lookup and destruction.
--b.
WARNING: multiple messages have this Message-ID (diff)
From: Bruce Fields <bfields@fieldses.org>
To: Jeff Layton <jlayton@poochiereds.net>
Cc: David Windsor <dwindsor@gmail.com>,
linux-nfs@vger.kernel.org, netdev@vger.kernel.org,
kernel-hardening@lists.openwall.com,
Kees Cook <keescook@chromium.org>,
"Reshetova, Elena" <elena.reshetova@intel.com>
Subject: [kernel-hardening] Re: [RFC][PATCH] nfsd: add +1 to reference counting scheme for struct nfsd4_session
Date: Sat, 11 Feb 2017 20:15:21 -0500 [thread overview]
Message-ID: <20170212011521.GD2768@fieldses.org> (raw)
In-Reply-To: <1486816302.4233.29.camel@poochiereds.net>
On Sat, Feb 11, 2017 at 07:31:42AM -0500, Jeff Layton wrote:
> The basic idea here is that nfsv4 sessions have a "resting state" of 0.
> We want to keep them around, but if they go "dead" then we we'll tear
> them down if they aren't actively in use at the time. So, we still free
> the thing when the refcount goes to zero, but we have an extra condition
> before we free it on the put -- that the session is also "dead" (meaning
> that the client asked us to destroy it).
>
> Your patch doesn't look like it'll break anything, but I personally find
> it harder to follow that way. The freeable reference state will be 1
> instead of the normal 0.
Alas, I don't have any examples in mind, but doesn't this pattern happen
all over?
You have objects that live in some data structure. They're freed only
when they're removed from the data structure. You want removal to fail
whenever they're in use.
So it's natural to use an atomic counter to track the number of external
users and some other lock to serialize lookup and destruction.
--b.
next prev parent reply other threads:[~2017-02-12 1:15 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-09 7:38 [RFC][PATCH] nfsd: add +1 to reference counting scheme for struct nfsd4_session David Windsor
2017-02-09 7:38 ` [kernel-hardening] " David Windsor
2017-02-09 7:38 ` David Windsor
2017-02-11 6:42 ` David Windsor
2017-02-11 6:42 ` [kernel-hardening] " David Windsor
[not found] ` <CAEXv5_jUa8Av4JABoKSAueiLHSLzibMvaE-8DrVcxZHFceckMg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-02-11 12:31 ` Jeff Layton
2017-02-11 12:31 ` [kernel-hardening] " Jeff Layton
2017-02-11 12:31 ` Jeff Layton
[not found] ` <1486816302.4233.29.camel-vpEMnDpepFuMZCB2o+C8xQ@public.gmane.org>
2017-02-11 14:01 ` David Windsor
2017-02-11 14:01 ` [kernel-hardening] " David Windsor
2017-02-11 14:01 ` David Windsor
2017-02-11 14:09 ` Jeff Layton
2017-02-11 14:09 ` [kernel-hardening] " Jeff Layton
[not found] ` <CAEXv5_gd7F-eaazzU1BWPzH4huhEcO1Y-FWov5UP9T+6R+fv-A-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-02-13 10:38 ` Christoph Hellwig
2017-02-13 10:38 ` [kernel-hardening] " Christoph Hellwig
2017-02-13 10:38 ` Christoph Hellwig
[not found] ` <20170213103815.GA5131-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
2017-02-13 11:42 ` David Windsor
2017-02-13 11:42 ` [kernel-hardening] " David Windsor
2017-02-13 11:42 ` David Windsor
[not found] ` <CAEXv5_g=DS4wk0mgZuw-doVCqountb-CxZki1LOoQH-P7W1U4A-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-02-13 12:12 ` Christoph Hellwig
2017-02-13 12:12 ` [kernel-hardening] " Christoph Hellwig
2017-02-13 12:12 ` Christoph Hellwig
2017-02-14 13:48 ` David Windsor
2017-02-14 13:48 ` [kernel-hardening] " David Windsor
2017-02-12 1:15 ` Bruce Fields [this message]
2017-02-12 1:15 ` Bruce Fields
2017-02-12 1:15 ` Bruce Fields
2017-02-12 1:42 ` David Windsor
2017-02-12 1:42 ` [kernel-hardening] " David Windsor
2017-02-13 10:54 ` Hans Liljestrand
2017-02-13 10:54 ` Hans Liljestrand
2017-02-13 11:46 ` David Windsor
[not found] ` <CAEXv5_hP39k7HSLP-G_khx7MMQHnk=8Z5caa+U5n3bYvUTE1gQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-02-15 16:45 ` Bruce Fields
2017-02-15 16:45 ` Bruce Fields
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