Re: [PATCH] futex: bugfix for futex-key conflict when futex usehugepage

[Mel Gorman]

On Wed, May 15, 2013 at 09:57:03PM +0800, Zhang Yi wrote:
> The futex-keys of processes share futex determined by page-offset,
> mapping-host, and mapping-index of the user space address. User
> appications using hugepage for futex may lead to futex-key conflict.
> 
> Assume there are two or more futexes in diffrent normal pages of the
> hugepage, and each futex has the same offset in its normal page,
> causing all the futexes have the same futex-key.
> 
> This patch adds the normal page index in the compound page into
> the pgoff of futex-key.
> 
> Steps to reproduce the bug:
> 1. The 1st thread map a file of hugetlbfs, and use the return address
> as the 1st mutex's address, and use the return address with PAGE_SIZE
> added as the 2nd mutex's address.
> 2. The 1st thread initialize the two mutexes with pshared attribute,
> and lock the two mutexes.
> 3. The 1st thread create the 2nd thread, and the 2nd thread block on
> the 1st mutex.
> 4. The 1st thread create the 3rd thread, and the 3rd thread block on
> the 2nd mutex.
> 5. The 1st thread unlock the 2nd mutex, the 3rd thread cannot take
> the 2nd mutex, and may block forever.
> 
> 
> Signed-off-by: Zhang Yi <zhang.yi20@xxxxxxxxxx>
> Tested-by: Ma Chenggong <ma.chenggong@xxxxxxxxxx>
> Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Reviewed-by: Darren Hart <dvhart@xxxxxxxxxxxxxxx>
> Reviewed-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Reviewed-by: Mel Gorman <mgorman@xxxxxxx>
> Reviewed-by: Liu Dong <liu.dong3@xxxxxxxxxx>
> Reviewed-by: Cui Yunfeng <cui.yunfeng@xxxxxxxxxx>
> Reviewed-by: Lu Zhongjun <lu.zhongjun@xxxxxxxxxx>
> Reviewed-by: Jiang Biao <jiang.biao2@xxxxxxxxxx>
> 

Did all these people really review it? I just whinged about the last patch
and didn't put a Reviewed-by on it. That said, I don't actually have a
problem with this patch and I assumed it passed your testing so

Reviewed-by: Mel Gorman <mgorman@xxxxxxx>

The others might not agree though.

I note the conversion from int offset to long offset in futex_key appears
to have gotten lost. Is that in a separate cleanup patch now?

-- 
Mel Gorman
SUSE Labs
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