Hi Vlastimil, On 02/07/2014 07:58 PM, Hannes Frederic Sowa wrote:
On Fri, Jan 31, 2014 at 03:40:38PM +0100, Vlastimil Babka wrote:From: Vlastimil Babka <vbabka@xxxxxxx> Date: Fri, 31 Jan 2014 11:50:21 +0100 Subject: [PATCH] mm: include VM_MIXEDMAP flag in the VM_SPECIAL list to avoid m(un)locking Daniel Borkmann reported a bug with VM_BUG_ON assertions failing where munlock_vma_pages_range() thinks it's unexpectedly in the middle of a THP page. This can be reproduced in tools/testing/selftests/net/ by running make and then ./psock_tpacket. The problem is that an order=2 compound page (allocated by alloc_one_pg_vec_page() is part of the munlocked VM_MIXEDMAP vma (mapped by packet_mmap()) and mistaken for a THP page and assumed to be order=9. The checks for THP in munlock came with commit ff6a6da60b89 ("mm: accelerate munlock() treatment of THP pages"), i.e. since 3.9, but did not trigger a bug. It just makes munlock_vma_pages_range() skip such compound pages until the next 512-pages-aligned page, when it encounters a head page. This is however not a problem for vma's where mlocking has no effect anyway, but it can distort the accounting. Since commit 7225522bb ("mm: munlock: batch non-THP page isolation and munlock+putback using pagevec") this can trigger a VM_BUG_ON in PageTransHuge() check. This patch fixes the issue by adding VM_MIXEDMAP flag to VM_SPECIAL - a list of flags that make vma's non-mlockable and non-mergeable. The reasoning is that VM_MIXEDMAP vma's are similar to VM_PFNMAP, which is already on the VM_SPECIAL list, and both are intended for non-LRU pages where mlocking makes no sense anyway.
Thanks a lot for your efforts. Is your patch queued up somewhere for mainline and stable?
I also ran into this problem and wanted to ask what the status of this patch is? Does it need further testing? I can surely help with that. ;) Thanks, Hannes
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