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Date:   Tue, 1 Dec 2020 16:31:04 -0500
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Axel Rasmussen <axelrasmussen@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Chinwen Chang <chinwen.chang@mediatek.com>,
        Daniel Jordan <daniel.m.jordan@oracle.com>,
        David Rientjes <rientjes@google.com>,
        Davidlohr Bueso <dbueso@suse.de>,
        Ingo Molnar <mingo@redhat.com>, Jann Horn <jannh@google.com>,
        Laurent Dufour <ldufour@linux.ibm.com>,
        Michel Lespinasse <walken@google.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Vlastimil Babka <vbabka@suse.cz>,
        Yafang Shao <laoar.shao@gmail.com>, davem@davemloft.net,
        dsahern@kernel.org, gregkh@linuxfoundation.org, kuba@kernel.org,
        liuhangbin@gmail.com, tj@kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH v2] mm: mmap_lock: fix use-after-free race and css ref
 leak in tracepoints
Message-ID: <20201201163104.5d178986@gandalf.local.home>
In-Reply-To: <20201201162847.654f3013@gandalf.local.home>
References: <20201201203249.4172751-1-axelrasmussen@google.com>
        <20201201162847.654f3013@gandalf.local.home>
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On Tue, 1 Dec 2020 16:28:47 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Tue,  1 Dec 2020 12:32:49 -0800
> Axel Rasmussen <axelrasmussen@google.com> wrote:
> 
> > +/* Called with reg_lock held. */  
> 
> The above comment is reduntant, as the lockdep_is_held() below also suggest
> that it is ;-)
>


> 
> >  static inline char *get_memcg_path_buf(void)
> >  {
> > +	char *buf;
> >  	int idx;
> >  
> > +	rcu_read_lock();  
> 
> The caller of get_mm_memcg_path() has preemption disabled, which is also
> now an RCU lock. So the rcu_read_lock() is somewhat redundant.


BTW, both of these comments are FYI. You can keep the comment and keep the
rcu_read_lock(). I was just stating that they are redundant, but keeping
them may make the code a bit more robust.

-- Steve