From fd584fb6fa6d48e1fae1077d2ab0021ae9c98edf Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.cz>
Date: Wed, 10 Jul 2019 11:31:01 +0200
Subject: [PATCH] mm: migrate: Fix race with __find_get_block()

Signed-off-by: Jan Kara <jack@suse.cz>
---
 include/trace/events/migrate.h | 42 ++++++++++++++++++++++++++++++++++++++++++
 mm/migrate.c                   |  8 +++++++-
 2 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/include/trace/events/migrate.h b/include/trace/events/migrate.h
index 705b33d1e395..15473a508216 100644
--- a/include/trace/events/migrate.h
+++ b/include/trace/events/migrate.h
@@ -70,6 +70,48 @@ TRACE_EVENT(mm_migrate_pages,
 		__print_symbolic(__entry->mode, MIGRATE_MODE),
 		__print_symbolic(__entry->reason, MIGRATE_REASON))
 );
+
+TRACE_EVENT(mm_migrate_buffers_begin,
+
+	TP_PROTO(struct address_space *mapping, unsigned long index),
+
+	TP_ARGS(mapping, index),
+
+	TP_STRUCT__entry(
+		__field(unsigned long,	mapping)
+		__field(unsigned long,	index)
+	),
+
+	TP_fast_assign(
+		__entry->mapping	= (unsigned long)mapping;
+		__entry->index		= index;
+	),
+
+	TP_printk("mapping=%lx index=%lu", __entry->mapping, __entry->index)
+);
+
+TRACE_EVENT(mm_migrate_buffers_end,
+
+	TP_PROTO(struct address_space *mapping, unsigned long index, int rc),
+
+	TP_ARGS(mapping, index, rc),
+
+	TP_STRUCT__entry(
+		__field(unsigned long,	mapping)
+		__field(unsigned long,	index)
+		__field(int,		rc)
+	),
+
+	TP_fast_assign(
+		__entry->mapping	= (unsigned long)mapping;
+		__entry->index		= index;
+		__entry->rc		= rc;
+	),
+
+	TP_printk("mapping=%lx index=%lu rc=%d", __entry->mapping, __entry->index, __entry->rc)
+);
+
+
 #endif /* _TRACE_MIGRATE_H */
 
 /* This part must be outside protection */
diff --git a/mm/migrate.c b/mm/migrate.c
index e9594bc0d406..bce0f1b03a60 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -763,6 +763,7 @@ static int __buffer_migrate_page(struct address_space *mapping,
 recheck_buffers:
 		busy = false;
 		spin_lock(&mapping->private_lock);
+		trace_mm_migrate_buffers_begin(mapping, page->index);
 		bh = head;
 		do {
 			if (atomic_read(&bh->b_count)) {
@@ -771,12 +772,13 @@ static int __buffer_migrate_page(struct address_space *mapping,
 			}
 			bh = bh->b_this_page;
 		} while (bh != head);
-		spin_unlock(&mapping->private_lock);
 		if (busy) {
 			if (invalidated) {
 				rc = -EAGAIN;
 				goto unlock_buffers;
 			}
+			trace_mm_migrate_buffers_end(mapping, page->index, -EAGAIN);
+			spin_unlock(&mapping->private_lock);
 			invalidate_bh_lrus();
 			invalidated = true;
 			goto recheck_buffers;
@@ -809,6 +811,10 @@ static int __buffer_migrate_page(struct address_space *mapping,
 
 	rc = MIGRATEPAGE_SUCCESS;
 unlock_buffers:
+	if (check_refs) {
+		trace_mm_migrate_buffers_end(mapping, page->index, rc);
+		spin_unlock(&mapping->private_lock);
+	}
 	bh = head;
 	do {
 		unlock_buffer(bh);
-- 
2.16.4