Messages in this thread | | | From | KOSAKI Motohiro <> | Date | Tue, 1 May 2012 10:37:20 -0400 | Subject | Re: [PATCH] Describe race of direct read and fork for unaligned buffers |
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> Hello, > > Thank you revisit this. But as far as my remember is correct, this issue is NOT > unaligned access issue. It's just get_user_pages(_fast) vs fork race issue. i.e. > DIRECT_IO w/ multi thread process should not use fork().
The problem is, fork (and its COW logic) assume new access makes cow break, But page table protection can't detect a DMA write. Therefore DIO may override shared page data.
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