Re: [Xen-devel] [PATCH] MCE: Fix race condition in mctelem_reserve

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 22/01/14 10:50, Frediano Ziglio wrote:
> These lines (in mctelem_reserve)
> 
> 
>         newhead = oldhead->mcte_next;
>         if (cmpxchgptr(freelp, oldhead, newhead) == oldhead) {
> 
> are racy. After you read the newhead pointer it can happen that another
> flow (thread or recursive invocation) change all the list but set head
> with same value. So oldhead is the same as *freelp but you are setting
> a new head that could point to whatever element (even already used).
> 
> This patch use instead a bit array and atomic bit operations.
> 
> Actually it use unsigned long instead of bitmap type as testing for
> all zeroes is easier.

bitmap_zero() does what you want.

David

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