From: dinghao.liu@zju.edu.cn
To: "Ira Weiny" <ira.weiny@intel.com>
Cc: "Dave Jiang" <dave.jiang@intel.com>,
"Vishal Verma" <vishal.l.verma@intel.com>,
"Dan Williams" <dan.j.williams@intel.com>,
nvdimm@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] nvdimm-btt: fix a potential memleak in btt_freelist_init
Date: Sun, 10 Dec 2023 00:27:43 +0800 (GMT+08:00) [thread overview]
Message-ID: <7360ec74.281bc.18c4f67fac7.Coremail.dinghao.liu@zju.edu.cn> (raw)
In-Reply-To: <6573a0451c4b7_1e7d27294ea@iweiny-mobl.notmuch>
> dinghao.liu@ wrote:
> > > Dave Jiang wrote:
>
> [snip]
>
> > > That said, this patch does not completely fix freelist from leaking in the
> > > following error path.
> > >
> > > discover_arenas()
> > > btt_freelist_init() -> ok (memory allocated)
> > > btt_rtt_init() -> fail
> > > goto out;
> > > (leak because arena is not yet on btt->arena_list)
> > > OR
> > > btt_maplocks_init() -> fail
> > > goto out;
> > > (leak because arena is not yet on btt->arena_list)
> > >
> >
> > Thanks for pointing out this issue! I rechecked discover_arenas() and found
> > that btt_rtt_init() may also trigger a memleak for the same reason as
> > btt_freelist_init(). Also, I checked another call trace:
> >
> > btt_init() -> btt_meta_init() -> btt_maplocks_init()
> >
> > I think there is a memleak if btt_maplocks_init() succeeds but an error
> > happens in btt_init() after btt_meta_init() (e.g., when btt_blk_init()
> > returns an error). Therefore, we may need to fix three functions.
>
> Yea I think we need to trace this code better. This is why devm_ is nice for
> memory allocated for the life of the device.
>
> >
> > > This error could be fixed by adding to arena_list earlier but devm_*()
> > > also takes care of this without having to worry about that logic.
> > >
> > > On normal operation all of this memory can be free'ed with the
> > > corresponding devm_kfree() and/or devm_add_action_*() calls if arenas come
> > > and go. I'm not sure off the top of my head.
> > >
> > > In addition, looking at this code. discover_arenas() could make use of
> > > the scoped based management for struct btt_sb *super!
> > >
> > > Dinghao would you be willing to submit a series of 2 or 3 patches to fix
> > > the above issues?
> > >
> >
> > Sure. Currently I plan to send 2 patches as follows:
> > 1. Using devm_kcalloc() to replace kcalloc() in btt_freelist_init(),
> > btt_rtt_init(), and btt_maplocks_init(), and removing the corresponding
> > kfree in free_arenas(). I checked some uses of devm_kcalloc() and it
> > seems that we need not to call devm_kfree(). The memory is automatically
> > freed on driver detach, right?
>
> On device put yes. So if these allocations are scoped to the life of the
> device there would be no reason to call devm_kfree() on them at all. I was not
> sure if they got reallocated at some point or not.
>
> > 2. Using the scoped based management for struct btt_sb *super (not a bug,
> > but it could improve the code).
>
> Good!
>
> >
> > I'm not quite sure whether my understanding or bug fixing plan is correct.
> > If there are any issues, please correct me, thanks!
>
> The above sounds right.
> Ira
Thanks for the review! I will send the patches soon.
Regards,
Dinghao
prev parent reply other threads:[~2023-12-09 16:27 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-07 3:43 [PATCH] nvdimm-btt: fix a potential memleak in btt_freelist_init Dinghao Liu
2023-12-07 15:43 ` Dave Jiang
2023-12-07 20:46 ` Ira Weiny
2023-12-08 6:35 ` dinghao.liu
2023-12-08 23:01 ` Ira Weiny
2023-12-09 16:27 ` dinghao.liu [this message]
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