linux-kernel - Re: [PATCH] pinctrl: use non-devm kmalloc versions for free functions

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Date:   Thu, 11 May 2017 15:20:58 +0100
From:   Andre Przywara <andre.przywara@....com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Tejun Heo <tj@...nel.org>, Icenowy Zheng <icenowy@...c.xyz>,
        Adam Borowski <kilobyte@...band.pl>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Chen-Yu Tsai <wens@...e.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] pinctrl: use non-devm kmalloc versions for free functions

Hi Linus,

On 11/05/17 15:01, Linus Walleij wrote:
> On Thu, May 4, 2017 at 1:57 AM, Andre Przywara <andre.przywara@....com> wrote:
> 
>> When a pinctrl driver gets interrupted during its probe process
>> (returning -EPROBE_DEFER), the devres system cleans up all allocated
>> resources. During this process it calls pinmux_generic_free_functions()
>> and pinctrl_generic_free_groups(), which in turn use managed kmalloc
>> calls for temporarily allocating some memory. Now those calls seem to
>> get added to the devres list, but are apparently not covered by the
>> cleanup process, because this is actually just running and iterating the
>> existing list. This leads to those mallocs being left with the device,
>> which the devres manager complains about when the driver eventually gets
>> probed again:
>> [    0.825239] ------------[ cut here ]------------
>> [    0.825256] WARNING: CPU: 1 PID: 89 at drivers/base/dd.c:349 driver_probe_device+0x2ac/0x2e8
>> [    0.825258] Modules linked in:
>> [    0.825262]
>> [    0.825270] CPU: 1 PID: 89 Comm: kworker/1:1 Not tainted 4.11.0 #307
>> [    0.825272] Hardware name: Pine64+ (DT)
>> [    0.825283] Workqueue: events deferred_probe_work_func
>> [    0.825288] task: ffff80007c19c100 task.stack: ffff80007c16c000
>> [    0.825292] PC is at driver_probe_device+0x2ac/0x2e8
>> [    0.825296] LR is at driver_probe_device+0x108/0x2e8
>> [    0.825300] pc : [<ffff000008559234>] lr : [<ffff000008559090>] pstate: 20000045
>> ....
>> This warning is triggered because the devres list is not empty. In this
>> case the allocations were using 0 bytes, so no real leaks, but still this
>> ugly warning.
>> Looking more closely at these *cleanup* functions, devm_kzalloc() is actually
>> not needed, because the memory is just allocated temporarily and can be
>> freed just before returning from this function.
>> So fix this issue by using the bog standard kcalloc() call instead of
>> devm_kzalloc() and kfree()ing the memory at the end.
>>
>> This fixes above warnings on boot, which can be observed on *some* builds
>> for the Pine64, where the pinctrl driver gets loaded early, but it missing
>> resources, so gets deferred and is loaded again (successfully) later.
>> kernelci caught this as well [1].
>>
>> Signed-off-by: Andre Przywara <andre.przywara@....com>
>>
>> [1] https://storage.kernelci.org/net-next/master/v4.11-rc8-2122-gc08bac03d289/arm64/defconfig/lab-baylibre-seattle/boot-sun50i-a64-pine64-plus.html
>> ---
>> Hi,
>>
>> not sure this is the right fix, I am open to suggestions.
> 
> I have queued this as a tentative v4.12-rc1 fix, but a bit undertain.
> 
> Tejun, do I read your comments on the patch as an ACK?

Tejun and I were wondering why we need this "create an array with the
indices" in the first place. If we can just call radix_tree_delete()
directly from the radix_tree_for_each_slot() loop, we can have a much
better fix (omitting the memory allocation at all)

Linus, can you shed some light if this array creation serves some purpose?

Cheers,
Andre.