On Thu, 1 Aug 2013 21:29:59 -0400 Ed Cashin <ecas...@coraid.com> wrote:
> As discussed previously, 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. > > It is not OK to increment the _count of a compound page tail, > though, since the VM layer will VM_BUG_ON a non-zero _count. > Block users that do direct I/O can result in the aoe driver > seeing compound page tails in bios. In that case, the same logic > works as long as the head of the compound page is used instead of > the tails. This patch handles compound pages and does not BUG. > > It relies on the block layer user leaving the relationship > between the page tail and its head alone for the duration between > the submission of the bio and its completion, whether successful > or not. What are the end-user-visible effects of the problem which is being fixed? Please always include this info when fixing bugs so that others can work out what kernel version(s) need the patch. -- 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/
