Subject: [PATCH RFC PKS/PMEM 06/58] kmap: Introduce k[un]map_thread debugging

From: [email-masked]
Date: Fri, 9 Oct 2020 12:49:41 -0700

From: Ira Weiny <[email-masked]>

Most kmap() callers use the map within a single thread and have no need
for the protection domain to be enabled globally.

To differentiate these kmap users, new k[un]map_thread() calls were
introduced which are thread local.

To aid in debugging the new use of kmap_thread(), add a reference count,
a check on that count, and tracing to ID where mapping errors occur.

Cc: Juri Lelli <[email-masked]>
Cc: Vincent Guittot <[email-masked]>
Cc: Dietmar Eggemann <[email-masked]>
Cc: Steven Rostedt <[email-masked]>
Cc: Ben Segall <[email-masked]>
Cc: Mel Gorman <[email-masked]>
Signed-off-by: Ira Weiny <[email-masked]>
---
 include/linux/highmem.h            |  5 +++
 include/linux/sched.h              |  5 +++
 include/trace/events/kmap_thread.h | 56 ++++++++++++++++++++++++++++++
 init/init_task.c                   |  3 ++
 kernel/fork.c                      | 15 ++++++++
 lib/Kconfig.debug                  |  8 +++++
 mm/debug.c                         | 23 ++++++++++++
 7 files changed, 115 insertions(+)
 create mode 100644 include/trace/events/kmap_thread.h

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index ef7813544719..22d1c000802e 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -247,6 +247,10 @@ static inline void kunmap(struct page *page)
 	__kunmap(page, true);
 }
 
+#ifdef CONFIG_DEBUG_KMAP_THREAD
+void *kmap_thread(struct page *page);
+void kunmap_thread(struct page *page);
+#else
 static inline void *kmap_thread(struct page *page)
 {
 	return __kmap(page, false);
@@ -255,6 +259,7 @@ static inline void kunmap_thread(struct page *page)
 {
 	__kunmap(page, false);
 }
+#endif
 
 /*
  * Prevent people trying to call kunmap_atomic() as if it were kunmap()
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 25d97ab6c757..4627ea4a49e6 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1318,6 +1318,11 @@ struct task_struct {
 #ifdef CONFIG_ZONE_DEVICE_ACCESS_PROTECTION
 	unsigned int			dev_page_access_ref;
 #endif
+
+#ifdef CONFIG_DEBUG_KMAP_THREAD
+	unsigned int			kmap_thread_cnt;
+#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/include/trace/events/kmap_thread.h b/include/trace/events/kmap_thread.h
new file mode 100644
index 000000000000..e7143cfe0daf
--- /dev/null
+++ b/include/trace/events/kmap_thread.h
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0 OR Linux-OpenIB */
+
+/*
+ * Copyright (c) 2020 Intel Corporation.  All rights reserved.
+ *
+ */
+
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM kmap_thread
+
+#if !defined(_TRACE_KMAP_THREAD_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_KMAP_THREAD_H
+
+#include <linux/tracepoint.h>
+
+DECLARE_EVENT_CLASS(kmap_thread_template,
+	TP_PROTO(struct task_struct *tsk, struct page *page,
+		 void *caller_addr, int cnt),
+	TP_ARGS(tsk, page, caller_addr, cnt),
+
+	TP_STRUCT__entry(
+		__field(int, pid)
+		__field(struct page *, page)
+		__field(void *, caller_addr)
+		__field(int, cnt)
+	),
+
+	TP_fast_assign(
+		__entry->pid = tsk->pid;
+		__entry->page = page;
+		__entry->caller_addr = caller_addr;
+		__entry->cnt = cnt;
+	),
+
+	TP_printk("PID %d; (%d) %pS %p",
+		__entry->pid,
+		__entry->cnt,
+		__entry->caller_addr,
+		__entry->page
+	)
+);
+
+DEFINE_EVENT(kmap_thread_template, kmap_thread,
+	TP_PROTO(struct task_struct *tsk, struct page *page,
+		 void *caller_addr, int cnt),
+	TP_ARGS(tsk, page, caller_addr, cnt));
+
+DEFINE_EVENT(kmap_thread_template, kunmap_thread,
+	TP_PROTO(struct task_struct *tsk, struct page *page,
+		 void *caller_addr, int cnt),
+	TP_ARGS(tsk, page, caller_addr, cnt));
+
+
+#endif /* _TRACE_KMAP_THREAD_H */
+
+#include <trace/define_trace.h>
diff --git a/init/init_task.c b/init/init_task.c
index 9b39f25de59b..19f09965eb34 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -212,6 +212,9 @@ struct task_struct init_task
 #ifdef CONFIG_ZONE_DEVICE_ACCESS_PROTECTION
 	.dev_page_access_ref = 0,
 #endif
+#ifdef CONFIG_DEBUG_KMAP_THREAD
+	.kmap_thread_cnt = 0,
+#endif
 };
 EXPORT_SYMBOL(init_task);
 
diff --git a/kernel/fork.c b/kernel/fork.c
index b6a3ee328a89..2c66e49b7614 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -722,6 +722,17 @@ static inline void put_signal_struct(struct signal_struct *sig)
 		free_signal_struct(sig);
 }
 
+#ifdef CONFIG_DEBUG_KMAP_THREAD
+static void check_outstanding_kmap_thread(struct task_struct *tsk)
+{
+	if (tsk->kmap_thread_cnt)
+		pr_warn(KERN_ERR "WARNING: PID %d; Failed to kunmap_thread() [cnt %d]\n",
+			tsk->pid, tsk->kmap_thread_cnt);
+}
+#else
+static void check_outstanding_kmap_thread(struct task_struct *tsk) { }
+#endif
+
 void __put_task_struct(struct task_struct *tsk)
 {
 	WARN_ON(!tsk->exit_state);
@@ -734,6 +745,7 @@ void __put_task_struct(struct task_struct *tsk)
 	exit_creds(tsk);
 	delayacct_tsk_free(tsk);
 	put_signal_struct(tsk->signal);
+	check_outstanding_kmap_thread(tsk);
 
 	if (!profile_handoff_task(tsk))
 		free_task(tsk);
@@ -943,6 +955,9 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 #endif
 #ifdef CONFIG_ZONE_DEVICE_ACCESS_PROTECTION
 	tsk->dev_page_access_ref = 0;
+#endif
+#ifdef CONFIG_DEBUG_KMAP_THREAD
+	tsk->kmap_thread_cnt = 0;
 #endif
 	return tsk;
 
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index f015c09ba5a1..6507b43d5b0c 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -858,6 +858,14 @@ config DEBUG_HIGHMEM
 	  This option enables additional error checking for high memory
 	  systems.  Disable for production systems.
 
+config DEBUG_KMAP_THREAD
+	bool "Kmap debugging"
+	depends on DEBUG_KERNEL
+	help
+	  This option enables additional error checking for kernel mapping code
+	  specifically the k[un]map_thread() calls.  Disable for production
+	  systems.
+
 config HAVE_DEBUG_STACKOVERFLOW
 	bool
 
diff --git a/mm/debug.c b/mm/debug.c
index ca8d1cacdecc..68d186f3570e 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -320,3 +320,26 @@ void page_init_poison(struct page *page, size_t size)
 }
 EXPORT_SYMBOL_GPL(page_init_poison);
 #endif		/* CONFIG_DEBUG_VM */
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/kmap_thread.h>
+
+#ifdef CONFIG_DEBUG_KMAP_THREAD
+void *kmap_thread(struct page *page)
+{
+	trace_kmap_thread(current, page, __builtin_return_address(0),
+			  current->kmap_thread_cnt);
+	current->kmap_thread_cnt++;
+	return __kmap(page, false);
+}
+EXPORT_SYMBOL_GPL(kmap_thread);
+
+void kunmap_thread(struct page *page)
+{
+	__kunmap(page, false);
+	current->kmap_thread_cnt--;
+	trace_kunmap_thread(current, page, __builtin_return_address(0),
+			    current->kmap_thread_cnt);
+}
+EXPORT_SYMBOL_GPL(kunmap_thread);
+#endif
-- 
2.28.0.rc0.12.gb6a658bd00c9