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authorJohannes Weiner <hannes@cmpxchg.org>2016-09-30 15:11:29 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-09-30 15:26:52 -0700
commit22f2ac51b6d643666f4db093f13144f773ff3f3a (patch)
treed5a0830636a18b247b02a22602d57637f3bac110
parente3b3656ca63e23b5755183718df36fb9ff518b02 (diff)
mm: workingset: fix crash in shadow node shrinker caused by replace_page_cache_page()
Antonio reports the following crash when using fuse under memory pressure: kernel BUG at /build/linux-a2WvEb/linux-4.4.0/mm/workingset.c:346! invalid opcode: 0000 [#1] SMP Modules linked in: all of them CPU: 2 PID: 63 Comm: kswapd0 Not tainted 4.4.0-36-generic #55-Ubuntu Hardware name: System manufacturer System Product Name/P8H67-M PRO, BIOS 3904 04/27/2013 task: ffff88040cae6040 ti: ffff880407488000 task.ti: ffff880407488000 RIP: shadow_lru_isolate+0x181/0x190 Call Trace: __list_lru_walk_one.isra.3+0x8f/0x130 list_lru_walk_one+0x23/0x30 scan_shadow_nodes+0x34/0x50 shrink_slab.part.40+0x1ed/0x3d0 shrink_zone+0x2ca/0x2e0 kswapd+0x51e/0x990 kthread+0xd8/0xf0 ret_from_fork+0x3f/0x70 which corresponds to the following sanity check in the shadow node tracking: BUG_ON(node->count & RADIX_TREE_COUNT_MASK); The workingset code tracks radix tree nodes that exclusively contain shadow entries of evicted pages in them, and this (somewhat obscure) line checks whether there are real pages left that would interfere with reclaim of the radix tree node under memory pressure. While discussing ways how fuse might sneak pages into the radix tree past the workingset code, Miklos pointed to replace_page_cache_page(), and indeed there is a problem there: it properly accounts for the old page being removed - __delete_from_page_cache() does that - but then does a raw raw radix_tree_insert(), not accounting for the replacement page. Eventually the page count bits in node->count underflow while leaving the node incorrectly linked to the shadow node LRU. To address this, make sure replace_page_cache_page() uses the tracked page insertion code, page_cache_tree_insert(). This fixes the page accounting and makes sure page-containing nodes are properly unlinked from the shadow node LRU again. Also, make the sanity checks a bit less obscure by using the helpers for checking the number of pages and shadows in a radix tree node. Fixes: 449dd6984d0e ("mm: keep page cache radix tree nodes in check") Link: http://lkml.kernel.org/r/20160919155822.29498-1-hannes@cmpxchg.org Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Reported-by: Antonio SJ Musumeci <trapexit@spawn.link> Debugged-by: Miklos Szeredi <miklos@szeredi.hu> Cc: <stable@vger.kernel.org> [3.15+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/swap.h2
-rw-r--r--mm/filemap.c114
-rw-r--r--mm/workingset.c10
3 files changed, 63 insertions, 63 deletions
diff --git a/include/linux/swap.h b/include/linux/swap.h
index b17cc4830fa6..4a529c984a3f 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -257,6 +257,7 @@ static inline void workingset_node_pages_inc(struct radix_tree_node *node)
static inline void workingset_node_pages_dec(struct radix_tree_node *node)
{
+ VM_BUG_ON(!workingset_node_pages(node));
node->count--;
}
@@ -272,6 +273,7 @@ static inline void workingset_node_shadows_inc(struct radix_tree_node *node)
static inline void workingset_node_shadows_dec(struct radix_tree_node *node)
{
+ VM_BUG_ON(!workingset_node_shadows(node));
node->count -= 1U << RADIX_TREE_COUNT_SHIFT;
}
diff --git a/mm/filemap.c b/mm/filemap.c
index 8a287dfc5372..2d0986a64f1f 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -110,6 +110,62 @@
* ->tasklist_lock (memory_failure, collect_procs_ao)
*/
+static int page_cache_tree_insert(struct address_space *mapping,
+ struct page *page, void **shadowp)
+{
+ struct radix_tree_node *node;
+ void **slot;
+ int error;
+
+ error = __radix_tree_create(&mapping->page_tree, page->index, 0,
+ &node, &slot);
+ if (error)
+ return error;
+ if (*slot) {
+ void *p;
+
+ p = radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
+ if (!radix_tree_exceptional_entry(p))
+ return -EEXIST;
+
+ mapping->nrexceptional--;
+ if (!dax_mapping(mapping)) {
+ if (shadowp)
+ *shadowp = p;
+ if (node)
+ workingset_node_shadows_dec(node);
+ } else {
+ /* DAX can replace empty locked entry with a hole */
+ WARN_ON_ONCE(p !=
+ (void *)(RADIX_TREE_EXCEPTIONAL_ENTRY |
+ RADIX_DAX_ENTRY_LOCK));
+ /* DAX accounts exceptional entries as normal pages */
+ if (node)
+ workingset_node_pages_dec(node);
+ /* Wakeup waiters for exceptional entry lock */
+ dax_wake_mapping_entry_waiter(mapping, page->index,
+ false);
+ }
+ }
+ radix_tree_replace_slot(slot, page);
+ mapping->nrpages++;
+ if (node) {
+ workingset_node_pages_inc(node);
+ /*
+ * Don't track node that contains actual pages.
+ *
+ * Avoid acquiring the list_lru lock if already
+ * untracked. The list_empty() test is safe as
+ * node->private_list is protected by
+ * mapping->tree_lock.
+ */
+ if (!list_empty(&node->private_list))
+ list_lru_del(&workingset_shadow_nodes,
+ &node->private_list);
+ }
+ return 0;
+}
+
static void page_cache_tree_delete(struct address_space *mapping,
struct page *page, void *shadow)
{
@@ -561,7 +617,7 @@ int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
spin_lock_irqsave(&mapping->tree_lock, flags);
__delete_from_page_cache(old, NULL);
- error = radix_tree_insert(&mapping->page_tree, offset, new);
+ error = page_cache_tree_insert(mapping, new, NULL);
BUG_ON(error);
mapping->nrpages++;
@@ -584,62 +640,6 @@ int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
}
EXPORT_SYMBOL_GPL(replace_page_cache_page);
-static int page_cache_tree_insert(struct address_space *mapping,
- struct page *page, void **shadowp)
-{
- struct radix_tree_node *node;
- void **slot;
- int error;
-
- error = __radix_tree_create(&mapping->page_tree, page->index, 0,
- &node, &slot);
- if (error)
- return error;
- if (*slot) {
- void *p;
-
- p = radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
- if (!radix_tree_exceptional_entry(p))
- return -EEXIST;
-
- mapping->nrexceptional--;
- if (!dax_mapping(mapping)) {
- if (shadowp)
- *shadowp = p;
- if (node)
- workingset_node_shadows_dec(node);
- } else {
- /* DAX can replace empty locked entry with a hole */
- WARN_ON_ONCE(p !=
- (void *)(RADIX_TREE_EXCEPTIONAL_ENTRY |
- RADIX_DAX_ENTRY_LOCK));
- /* DAX accounts exceptional entries as normal pages */
- if (node)
- workingset_node_pages_dec(node);
- /* Wakeup waiters for exceptional entry lock */
- dax_wake_mapping_entry_waiter(mapping, page->index,
- false);
- }
- }
- radix_tree_replace_slot(slot, page);
- mapping->nrpages++;
- if (node) {
- workingset_node_pages_inc(node);
- /*
- * Don't track node that contains actual pages.
- *
- * Avoid acquiring the list_lru lock if already
- * untracked. The list_empty() test is safe as
- * node->private_list is protected by
- * mapping->tree_lock.
- */
- if (!list_empty(&node->private_list))
- list_lru_del(&workingset_shadow_nodes,
- &node->private_list);
- }
- return 0;
-}
-
static int __add_to_page_cache_locked(struct page *page,
struct address_space *mapping,
pgoff_t offset, gfp_t gfp_mask,
diff --git a/mm/workingset.c b/mm/workingset.c
index 69551cfae97b..617475f529f4 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -418,21 +418,19 @@ static enum lru_status shadow_lru_isolate(struct list_head *item,
* no pages, so we expect to be able to remove them all and
* delete and free the empty node afterwards.
*/
-
- BUG_ON(!node->count);
- BUG_ON(node->count & RADIX_TREE_COUNT_MASK);
+ BUG_ON(!workingset_node_shadows(node));
+ BUG_ON(workingset_node_pages(node));
for (i = 0; i < RADIX_TREE_MAP_SIZE; i++) {
if (node->slots[i]) {
BUG_ON(!radix_tree_exceptional_entry(node->slots[i]));
node->slots[i] = NULL;
- BUG_ON(node->count < (1U << RADIX_TREE_COUNT_SHIFT));
- node->count -= 1U << RADIX_TREE_COUNT_SHIFT;
+ workingset_node_shadows_dec(node);
BUG_ON(!mapping->nrexceptional);
mapping->nrexceptional--;
}
}
- BUG_ON(node->count);
+ BUG_ON(workingset_node_shadows(node));
inc_node_state(page_pgdat(virt_to_page(node)), WORKINGSET_NODERECLAIM);
if (!__radix_tree_delete_node(&mapping->page_tree, node))
BUG();

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