[patch 038/178] mm: page_owner: detect page_owner recursion via task_struct

[Andrew Morton <akpm@linux-foundation.org>]

From: Sergei Trofimovich <slyfox@gentoo.org>
Subject: mm: page_owner: detect page_owner recursion via task_struct

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 flag
in 'struct task_struct'.

The change make page_owner=on work on ia64 by 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]

Link: https://lkml.kernel.org/r/20210402115342.1463781-1-slyfox@gentoo.org
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/sched.h |    4 ++++
 mm/page_owner.c       |   32 ++++++++++----------------------
 2 files changed, 14 insertions(+), 22 deletions(-)

--- a/include/linux/sched.h~mm-page_owner-detect-page_owner-recursion-via-task_struct
+++ a/include/linux/sched.h
@@ -841,6 +841,10 @@ struct task_struct {
 	/* Stalled due to lack of memory */
 	unsigned			in_memstall:1;
 #endif
+#ifdef CONFIG_PAGE_OWNER
+	/* Used by page_owner=on to detect recursion in page tracking. */
+	unsigned			in_page_owner:1;
+#endif
 
 	unsigned long			atomic_flags; /* Flags requiring atomic access. */
 
--- a/mm/page_owner.c~mm-page_owner-detect-page_owner-recursion-via-task_struct
+++ a/mm/page_owner.c
@@ -98,42 +98,30 @@ static inline struct page_owner *get_pag
 	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.
+	 * Avoid recursion.
+	 *
+	 * Sometimes page metadata allocation tracking requires more
+	 * memory to be allocated:
+	 * - when new stack trace is saved to stack depot
+	 * - when backtrace itself is calculated (ia64)
 	 */
-	if (check_recursive_alloc(entries, nr_entries, _RET_IP_))
+	if (current->in_page_owner)
 		return dummy_handle;
+	current->in_page_owner = 1;
 
+	nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 2);
 	handle = stack_depot_save(entries, nr_entries, flags);
 	if (!handle)
 		handle = failure_handle;
 
+	current->in_page_owner = 0;
 	return handle;
 }
 
_