From d3798ae8c6f3767c726403c2ca6ecc317752c9dd Mon Sep 17 00:00:00 2001 From: Johannes Weiner Date: Tue, 4 Oct 2016 22:02:08 +0200 Subject: mm: filemap: don't plant shadow entries without radix tree node When the underflow checks were added to workingset_node_shadow_dec(), they triggered immediately: kernel BUG at ./include/linux/swap.h:276! invalid opcode: 0000 [#1] SMP Modules linked in: isofs usb_storage fuse xt_CHECKSUM ipt_MASQUERADE nf_nat_masquerade_ipv4 tun nf_conntrack_netbios_ns nf_conntrack_broadcast ip6t_REJECT nf_reject_ipv6 soundcore wmi acpi_als pinctrl_sunrisepoint kfifo_buf tpm_tis industrialio acpi_pad pinctrl_intel tpm_tis_core tpm nfsd auth_rpcgss nfs_acl lockd grace sunrpc dm_crypt CPU: 0 PID: 20929 Comm: blkid Not tainted 4.8.0-rc8-00087-gbe67d60ba944 #1 Hardware name: System manufacturer System Product Name/Z170-K, BIOS 1803 05/06/2016 task: ffff8faa93ecd940 task.stack: ffff8faa7f478000 RIP: page_cache_tree_insert+0xf1/0x100 Call Trace: __add_to_page_cache_locked+0x12e/0x270 add_to_page_cache_lru+0x4e/0xe0 mpage_readpages+0x112/0x1d0 blkdev_readpages+0x1d/0x20 __do_page_cache_readahead+0x1ad/0x290 force_page_cache_readahead+0xaa/0x100 page_cache_sync_readahead+0x3f/0x50 generic_file_read_iter+0x5af/0x740 blkdev_read_iter+0x35/0x40 __vfs_read+0xe1/0x130 vfs_read+0x96/0x130 SyS_read+0x55/0xc0 entry_SYSCALL_64_fastpath+0x13/0x8f Code: 03 00 48 8b 5d d8 65 48 33 1c 25 28 00 00 00 44 89 e8 75 19 48 83 c4 18 5b 41 5c 41 5d 41 5e 5d c3 0f 0b 41 bd ef ff ff ff eb d7 <0f> 0b e8 88 68 ef ff 0f 1f 84 00 RIP page_cache_tree_insert+0xf1/0x100 This is a long-standing bug in the way shadow entries are accounted in the radix tree nodes. The shrinker needs to know when radix tree nodes contain only shadow entries, no pages, so node->count is split in half to count shadows in the upper bits and pages in the lower bits. Unfortunately, the radix tree implementation doesn't know of this and assumes all entries are in node->count. When there is a shadow entry directly in root->rnode and the tree is later extended, the radix tree implementation will copy that entry into the new node and and bump its node->count, i.e. increases the page count bits. Once the shadow gets removed and we subtract from the upper counter, node->count underflows and triggers the warning. Afterwards, without node->count reaching 0 again, the radix tree node is leaked. Limit shadow entries to when we have actual radix tree nodes and can count them properly. That means we lose the ability to detect refaults from files that had only the first page faulted in at eviction time. Fixes: 449dd6984d0e ("mm: keep page cache radix tree nodes in check") Signed-off-by: Johannes Weiner Reported-and-tested-by: Linus Torvalds Reviewed-by: Jan Kara Cc: Andrew Morton Cc: stable@vger.kernel.org Signed-off-by: Linus Torvalds --- mm/filemap.c | 46 ++++++++++++++++++++++++++++++---------------- 1 file changed, 30 insertions(+), 16 deletions(-) (limited to 'mm/filemap.c') diff --git a/mm/filemap.c b/mm/filemap.c index 2d0986a64f1f..96b9e9c30630 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -169,33 +169,35 @@ static int page_cache_tree_insert(struct address_space *mapping, static void page_cache_tree_delete(struct address_space *mapping, struct page *page, void *shadow) { - struct radix_tree_node *node; int i, nr = PageHuge(page) ? 1 : hpage_nr_pages(page); VM_BUG_ON_PAGE(!PageLocked(page), page); VM_BUG_ON_PAGE(PageTail(page), page); VM_BUG_ON_PAGE(nr != 1 && shadow, page); - if (shadow) { - mapping->nrexceptional += nr; - /* - * Make sure the nrexceptional update is committed before - * the nrpages update so that final truncate racing - * with reclaim does not see both counters 0 at the - * same time and miss a shadow entry. - */ - smp_wmb(); - } - mapping->nrpages -= nr; - for (i = 0; i < nr; i++) { - node = radix_tree_replace_clear_tags(&mapping->page_tree, - page->index + i, shadow); + struct radix_tree_node *node; + void **slot; + + __radix_tree_lookup(&mapping->page_tree, page->index + i, + &node, &slot); + + radix_tree_clear_tags(&mapping->page_tree, node, slot); + if (!node) { VM_BUG_ON_PAGE(nr != 1, page); - return; + /* + * We need a node to properly account shadow + * entries. Don't plant any without. XXX + */ + shadow = NULL; } + radix_tree_replace_slot(slot, shadow); + + if (!node) + break; + workingset_node_pages_dec(node); if (shadow) workingset_node_shadows_inc(node); @@ -219,6 +221,18 @@ static void page_cache_tree_delete(struct address_space *mapping, &node->private_list); } } + + if (shadow) { + mapping->nrexceptional += nr; + /* + * Make sure the nrexceptional update is committed before + * the nrpages update so that final truncate racing + * with reclaim does not see both counters 0 at the + * same time and miss a shadow entry. + */ + smp_wmb(); + } + mapping->nrpages -= nr; } /* -- cgit v1.2.3-58-ga151