On Aug 7, 2013, at 4:58 PM, Andrew Morton wrote: > On Thu, 1 Aug 2013 21:29:59 -0400 Ed Cashin <ecas...@coraid.com> wrote: > >> As discussed previously, > > I think I missed that. > >> the fact that some users of the block >> layer provide bios that point to pages with a zero _count means >> that it is not OK for the network layer to do a put_page on the >> skb frags during an skb_linearize, so the aoe driver gets a >> reference to pages in bios and puts the reference before ending >> the bio. And because it cannot use get_page on a page with a >> zero _count, it manipulates the value directly. > > Eh? What code is putting count==0 pages into bios? That sounds very > weird and broken.
I thought so in 2007 but couldn't solicit a clear "this is wrong" consensus from the discussion. http://article.gmane.org/gmane.linux.kernel/499197 https://lkml.org/lkml/2007/1/19/56 https://lkml.org/lkml/2006/12/18/230 We were seeing zero-count pages in bios from XFS, but Christoph Hellwig pointed out that kmalloced pages can also come from ext3 when it's doing log recovery, and they'll have zero page counts. I don't have a counter in the driver to track how often zero-count pages show up in bios, so I don't know how common it is these days. I would have been motivated to look if I had gotten the impression that there was any interest in identifying and eliminating cases where zero-count pages were being used in bios. -- Ed Cashin ecas...@coraid.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
