Messages in this thread | | | Date | Mon, 28 Jul 2008 16:03:16 -0500 | From | Eric Sandeen <> | Subject | Re: [PATCH] eCryptfs - use page_alloc not kmalloc to get a page of memory |
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Pekka Enberg wrote: > On Mon, Jul 28, 2008 at 11:35 PM, Andrew Morton > <akpm@linux-foundation.org> wrote: >> On Mon, 28 Jul 2008 11:13:03 -0500 >> Eric Sandeen <sandeen@redhat.com> wrote: >> >>> With SLUB debugging turned on in 2.6.26, I was getting memory corruption >>> when testing eCryptfs. The root cause turned out to be that eCryptfs >>> was doing kmalloc(PAGE_CACHE_SIZE); virt_to_page() and treating that >>> as a nice page-aligned chunk of memory. But at least with SLUB debugging >>> on, this is not always true, and the page we get from virt_to_page does >>> not necessarily match the PAGE_CACHE_SIZE worth of memory we got from >>> kmalloc. >>> >>> My simple testcase was 2 loops doing "rm -f fileX; cp /tmp/fileX ." for >>> 2 different multi-megabyte files. With this change I no longer see >>> the corruption. >> The fix applies to both 2.6.25 and to 2.6.26 and appears to be needed >> in both kernel versions, so I have tagged it for backporting into both. > > Hmm, SLUB will use the page allocator directly for PAGE_CACHE_SIZE > regadless of whether debugging is enabled or not...
For whatever reason, I did see non-page-aligned memory returned from kmalloc(PAGE_CACHE_SIZE), and I think this is what caused the problem once virt_to_page() was used to get hold of a page to pass around in the ecryptfs/crypto code...
-Eric
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