From: David Miller <davem@davemloft.net>
To: dwindsor@gmail.com
Cc: netdev@vger.kernel.org, keescook@chromium.org,
elena.reshetova@intel.com, ishkamiel@gmail.com
Subject: Re: Reference counting struct inet_peer
Date: Tue, 24 Jan 2017 14:20:35 -0500 (EST) [thread overview]
Message-ID: <20170124.142035.1532512255377175036.davem@davemloft.net> (raw)
In-Reply-To: <CAEXv5_j1cz1EUPgmAKO5OHxKcoHVLuPPVRs316CWyMpw8UtpRw@mail.gmail.com>
From: David Windsor <dwindsor@gmail.com>
Date: Mon, 23 Jan 2017 07:42:51 -0500
> struct inet_peer objects get freed when their reference count
> becomes -1, not 0 as is the usual case. Is there a reason why this
> is so?
inet peer entries that sit in the tree, but have no other reference
taken, have a reference count of zero.
Therefore, any entry which has a reference count of zero can be
safely garbage collected from the tree.
When the garbage collector purges entries with a zero refcnt, it
atomically sets the refcnt to -1 so that other threads of control
in RCU protected sections that still see this entry in the tree
will not be able to grab it for use.
The -1 marker is used as a synchronization mechanism between the
GC and lookup paths.
Once -1 is atomically set, the GC code knows that no external
reference can be created.
prev parent reply other threads:[~2017-01-24 19:20 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-23 12:42 Reference counting struct inet_peer David Windsor
2017-01-24 7:38 ` Julian Anastasov
2017-01-24 11:05 ` David Windsor
2017-01-24 19:20 ` David Miller [this message]
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