linux-kernel - Re: [PATCH 2/4] signal: Make flush_sigqueue() use free

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Date:   Fri, 22 Mar 2019 12:59:26 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Christopher Lameter <cl@...ux.com>
Cc:     Waiman Long <longman@...hat.com>, Oleg Nesterov <oleg@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        selinux@...r.kernel.org, Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Eric Paris <eparis@...isplace.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [PATCH 2/4] signal: Make flush_sigqueue() use free_q to release
 memory

On Fri, Mar 22, 2019 at 07:39:31PM +0000, Christopher Lameter wrote:
> On Fri, 22 Mar 2019, Waiman Long wrote:
> 
> > >
> > >> I am looking forward to it.
> > > There is also alrady rcu being used in these paths. kfree_rcu() would not
> > > be enough? It is an estalished mechanism that is mature and well
> > > understood.
> > >
> > In this case, the memory objects are from kmem caches, so they can't
> > freed using kfree_rcu().
> 
> Oh they can. kfree() can free memory from any slab cache.

Only for SLAB and SLUB.  SLOB requires that you pass a pointer to the
slab cache; it has no way to look up the slab cache from the object.