Hi Michal,
On Mon, Oct 24, 2016 at 05:26:04PM +0200, Michal Hocko wrote:
> @@ -155,44 +155,27 @@ static void page_cache_tree_delete(struct address_space *mapping,
> struct page *page, void *shadow)
> {
> struct radix_tree_node *node;
> - unsigned long index;
> - unsigned int offset;
> - unsigned int tag;
> void **slot;
>
> VM_BUG_ON(!PageLocked(page));
>
> __radix_tree_lookup(&mapping->page_tree, page->index, &node, &slot);
>
> - if (shadow) {
> - mapping->nrshadows++;
> - /*
> - * Make sure the nrshadows 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--;
> + radix_tree_clear_tags(&mapping->page_tree, node, slot);
>
> if (!node) {
> - /* Clear direct pointer tags in root node */
> - mapping->page_tree.gfp_mask &= __GFP_BITS_MASK;
> - radix_tree_replace_slot(slot, shadow);
> - return;
> - }
There is no need to include the refactoring of the tag clearing in the
stable backport. I already sent a simpler backport of this patch for
4.4 to Greg, attached here for reference:
>From ba2dae8c4ddcc70a1d7bb1478f4c7c6ffe130b6f Mon Sep 17 00:00:00 2001
From: Johannes Weiner <hannes@xxxxxxxxxxx>
Date: Fri, 21 Oct 2016 13:40:41 -0400
Subject: [PATCH] mm: filemap: don't plant shadow entries without radix tree
node
commit d3798ae8c6f3767c726403c2ca6ecc317752c9dd upstream.
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 <hannes@xxxxxxxxxxx>
Reported-and-tested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
---
mm/filemap.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/mm/filemap.c b/mm/filemap.c
index 1bb007624b53..fb52502d12f4 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -122,6 +122,14 @@ static void page_cache_tree_delete(struct address_space *mapping,
__radix_tree_lookup(&mapping->page_tree, page->index, &node, &slot);
+ if (!node) {
+ /*
+ * We need a node to properly account shadow
+ * entries. Don't plant any without. XXX
+ */
+ shadow = NULL;
+ }
+
if (shadow) {
mapping->nrshadows++;
/*
--
2.10.0
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