linux-kernel - Re: [RFC] does ioremap() cause memory leak?

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Message-ID: <e25b1da2-14fb-eeec-1a76-1756011535bb@huawei.com>
Date:   Tue, 2 Jan 2018 09:39:47 +0800
From:   Hanjun Guo <guohanjun@...wei.com>
To:     Xishi Qiu <qiuxishi@...wei.com>
CC:     Toshi Kani <toshi.kani@...com>, "H. Peter Anvin" <hpa@...or.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>, <lious.lilei@...ilicon.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        LinuxArm <linuxarm@...wei.com>
Subject: Re: [RFC] does ioremap() cause memory leak?

On 2017/12/23 13:32, Xishi Qiu wrote:
> On 2017/12/21 16:55, Xishi Qiu wrote:
> 
>> When we use iounmap() to free the mapping, it calls unmap_vmap_area() to clear page table,
>> but do not free the memory of page table, right?
>>
>> So when use ioremap() to mapping another area(incluce the area before), it may use
>> large mapping(e.g. ioremap_pmd_enabled()), so the original page table memory(e.g. pte memory)
>> will be lost, it cause memory leak, right?
> 
>  
> 
> So I have two questions for this scene.
> 
> 1. When the same virtual address allocated from ioremap, first is 4K size, second is 2M size, if Kernel would leak memory.
> 
> 2. Kernel modifies the old invalid 4K pagetable to 2M, but doesn`t follow the ARM break-before-make flow, CPU maybe get the old invalid 4K pagetable information, then Kernel would panic.

I sent a RFC patch for this one [1].

[1]: https://patchwork.kernel.org/patch/10134581/

Thanks
Hanjun