From fb32975d1ba6dc2aaa3c2e876e7220c8ec260397 Mon Sep 17 00:00:00 2001 From: Ed Cashin Date: Tue, 13 Aug 2013 16:00:53 -0700 Subject: [PATCH] aoe: adjust ref of head for compound page tails Fix a BUG which can trigger when direct-IO is used with AOE. 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. Signed-off-by: Ed Cashin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/block/aoe/aoecmd.c | 17 +++++++---------- 1 file changed, 7 insertions(+), 10 deletions(-) diff --git a/drivers/block/aoe/aoecmd.c b/drivers/block/aoe/aoecmd.c index 99cb944a002d..4d45dba7fb8f 100644 --- a/drivers/block/aoe/aoecmd.c +++ b/drivers/block/aoe/aoecmd.c @@ -906,16 +906,10 @@ bio_pageinc(struct bio *bio) int i; bio_for_each_segment(bv, bio, i) { - page = bv->bv_page; /* Non-zero page count for non-head members of - * compound pages is no longer allowed by the kernel, - * but this has never been seen here. + * compound pages is no longer allowed by the kernel. */ - if (unlikely(PageCompound(page))) - if (compound_trans_head(page) != page) { - pr_crit("page tail used for block I/O\n"); - BUG(); - } + page = compound_trans_head(bv->bv_page); atomic_inc(&page->_count); } } @@ -924,10 +918,13 @@ static void bio_pagedec(struct bio *bio) { struct bio_vec *bv; + struct page *page; int i; - bio_for_each_segment(bv, bio, i) - atomic_dec(&bv->bv_page->_count); + bio_for_each_segment(bv, bio, i) { + page = compound_trans_head(bv->bv_page); + atomic_dec(&page->_count); + } } static void