linux-kernel - Re: [PATCH] percpu: fix chunk range calculation

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Message-ID: <20111121211050.GK25776@google.com>
Date:	Mon, 21 Nov 2011 13:10:50 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Dave Young <dyoung@...hat.com>
Cc:	tim@...ecast.com, WANG Cong <xiyou.wangcong@...il.com>,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] percpu: fix chunk range calculation

On Fri, Nov 18, 2011 at 10:55:35AM -0800, Tejun Heo wrote:
> Percpu allocator recorded the cpus which map to the first and last
> units in pcpu_first/last_unit_cpu respectively and used them to
> determine the address range of a chunk - e.g. it assumed that the
> first unit has the lowest address in a chunk while the last unit has
> the highest address.
> 
> This simply isn't true.  Groups in a chunk can have arbitrary positive
> or negative offsets from the previous one and there is no guarantee
> that the first unit occupies the lowest offset while the last one the
> highest.
> 
> Fix it by actually comparing unit offsets to determine cpus occupying
> the lowest and highest offsets.  Also, rename pcu_first/last_unit_cpu
> to pcpu_low/high_unit_cpu to avoid confusion.
> 
> The chunk address range is used to flush cache on vmalloc area
> map/unmap and decide whether a given address is in the first chunk by
> per_cpu_ptr_to_phys() and the bug was discovered by invalid
> per_cpu_ptr_to_phys() translation for crash_note.
> 
> Kudos to Dave Young for tracking down the problem.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Reported-by: WANG Cong <xiyou.wangcong@...il.com>
> Reported-by: Dave Young <dyoung@...hat.com>
> LKML-Reference: <4EC21F67.10905@...hat.com>
> Cc: stable @kernel.org

BTW, waiting for Tested-by.  If someone gives me that, I'll push it
through percpu/for-fixes.

Thanks.

-- 
tejun
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