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Subject: Re: [PATCH 1/1] clk: tegra: tegra124-emc: Fix possible memory leak
To:     Stephen Boyd <sboyd@kernel.org>,
        Dmitry Osipenko <digetx@gmail.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        Michael Turquette <mturquette@baylibre.com>,
        Peter De Schrijver <pdeschrijver@nvidia.com>,
        Prashant Gaikwad <pgaikwad@nvidia.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        linux-clk <linux-clk@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-tegra <linux-tegra@vger.kernel.org>
References: <20210617082759.1008-1-thunder.leizhen@huawei.com>
 <162466387362.3259633.2364843071785127818@swboyd.mtv.corp.google.com>
From:   "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>
Message-ID: <a6f88419-2cb9-0717-7737-e4666cdcc211@huawei.com>
Date:   Sat, 26 Jun 2021 09:32:46 +0800
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On 2021/6/26 7:31, Stephen Boyd wrote:
> Quoting Zhen Lei (2021-06-17 01:27:59)
>> When krealloc() fails to expand the memory and returns NULL, the original
>> memory is not released. In this case, the original "timings" scale should
>> be maintained.
>>
>> Fixes: 888ca40e2843 ("clk: tegra: emc: Support multiple RAM codes")
>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>> ---
> 
> Looks correct, but when does krealloc() return NULL? My read of the
> kerneldoc is that it would return the original memory if the new
> allocation "failed".

That must be the wrong description in the document. For example, the original
100-byte memory needs to be expanded to 200 bytes. If the memory allocation fails,
a non-null pointer is returned. People must think they've applied for it and
continue to use it, the end result is memory crashed.

I don't think the kernel needs to be different from libc's realloc().

The implementation of __do_krealloc() illustrates this as well:
        /* If the object still fits, repoison it precisely. */
        if (ks >= new_size) {
                p = kasan_krealloc((void *)p, new_size, flags);
                return (void *)p;
        }

        ret = kmalloc_track_caller(new_size, flags);			//enlarge, allocate new memory
	if (ret && p) {
                memcpy(ret, kasan_reset_tag(p), ks);			//copy the old content from 'p' to new memory 'ret'
        }

	return ret;							//ret may be NULL, if kmalloc_track_caller() failed


> 
> Reviewed-by: Stephen Boyd <sboyd@kernel.org>
> 
> .
>