Before the change page_owner recursion was detected via fetching
backtrace and inspecting it for current instruction pointer.
It has a few problems:
- it is slightly slow as it requires extra backtrace and a linear
stack scan of the result
- it is too late to check if backtrace fetching required memory
allocation itself (ia64's unwinder requires it).
To simplify recursion tracking let's use page_owner recursion depth
as a counter in 'struct task_struct'.
The change make page_owner=on work on ia64 bu avoiding infinite
recursion in:
kmalloc()
-> __set_page_owner()
-> save_stack()
-> unwind() [ia64-specific]
-> build_script()
-> kmalloc()
-> __set_page_owner() [we short-circuit here]
-> save_stack()
-> unwind() [recursion]
CC: Ingo Molnar <mingo@xxxxxxxxxx>
CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CC: Juri Lelli <juri.lelli@xxxxxxxxxx>
CC: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
CC: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
CC: Ben Segall <bsegall@xxxxxxxxxx>
CC: Mel Gorman <mgorman@xxxxxxx>
CC: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
CC: linux-mm@xxxxxxxxx
Signed-off-by: Sergei Trofimovich <slyfox@xxxxxxxxxx>
---
include/linux/sched.h | 9 +++++++++
init/init_task.c | 3 +++
mm/page_owner.c | 41 +++++++++++++++++------------------------
3 files changed, 29 insertions(+), 24 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index ef00bb22164c..35771703fd89 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1371,6 +1371,15 @@ struct task_struct {
struct llist_head kretprobe_instances;
#endif
+#ifdef CONFIG_PAGE_OWNER
+ /*
+ * Used by page_owner=on to detect recursion in page tracking.
+ * Is it fine to have non-atomic ops here if we ever access
+ * this variable via current->page_owner_depth?
+ */
+ unsigned int page_owner_depth;
+#endif
+
/*
* New fields for task_struct should be added above here, so that
* they are included in the randomized portion of task_struct.
diff --git a/init/init_task.c b/init/init_task.c
index 3711cdaafed2..f579f2b2eca8 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -213,6 +213,9 @@ struct task_struct init_task
#ifdef CONFIG_SECCOMP
.seccomp = { .filter_count = ATOMIC_INIT(0) },
#endif
+#ifdef CONFIG_PAGE_OWNER
+ .page_owner_depth = 0,
+#endif
};
EXPORT_SYMBOL(init_task);
diff --git a/mm/page_owner.c b/mm/page_owner.c
index 7147fd34a948..422558605fcc 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -20,6 +20,16 @@
*/
#define PAGE_OWNER_STACK_DEPTH (16)
+/*
+ * How many reenters we allow to page_owner.
+ *
+ * Sometimes metadata allocation tracking requires more memory to be allocated:
+ * - when new stack trace is saved to stack depot
+ * - when backtrace itself is calculated (ia64)
+ * Instead of falling to infinite recursion give it a chance to recover.
+ */
+#define PAGE_OWNER_MAX_RECURSION_DEPTH (1)
+
struct page_owner {
unsigned short order;
short last_migrate_reason;
@@ -97,42 +107,25 @@ static inline struct page_owner *get_page_owner(struct page_ext *page_ext)
return (void *)page_ext + page_owner_ops.offset;
}
-static inline bool check_recursive_alloc(unsigned long *entries,
- unsigned int nr_entries,
- unsigned long ip)
-{
- unsigned int i;
-
- for (i = 0; i < nr_entries; i++) {
- if (entries[i] == ip)
- return true;
- }
- return false;
-}
-
static noinline depot_stack_handle_t save_stack(gfp_t flags)
{
unsigned long entries[PAGE_OWNER_STACK_DEPTH];
depot_stack_handle_t handle;
unsigned int nr_entries;
- nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 2);
-
- /*
- * We need to check recursion here because our request to
- * stackdepot could trigger memory allocation to save new
- * entry. New memory allocation would reach here and call
- * stack_depot_save_entries() again if we don't catch it. There is
- * still not enough memory in stackdepot so it would try to
- * allocate memory again and loop forever.
- */
- if (check_recursive_alloc(entries, nr_entries, _RET_IP_))
+ /* Avoid recursion. Used in stack trace generation code. */
+ if (current->page_owner_depth >= PAGE_OWNER_MAX_RECURSION_DEPTH)
return dummy_handle;
+ current->page_owner_depth++;
+
+ nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 2);
+
handle = stack_depot_save(entries, nr_entries, flags);
if (!handle)
handle = failure_handle;
+ current->page_owner_depth--;
return handle;
}
--
2.31.1
