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-rw-r--r--lib/Kconfig.debug9
-rw-r--r--lib/Makefile1
-rw-r--r--lib/test_free_pages.c42
-rw-r--r--mm/page_alloc.c3
4 files changed, 55 insertions, 0 deletions
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 0c781f912f9f..491789a793ae 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2367,6 +2367,15 @@ config TEST_HMM
If unsure, say N.
+config TEST_FREE_PAGES
+ tristate "Test freeing pages"
+ help
+ Test that a memory leak does not occur due to a race between
+ freeing a block of pages and a speculative page reference.
+ Loading this module is safe if your kernel has the bug fixed.
+ If the bug is not fixed, it will leak gigabytes of memory and
+ probably OOM your system.
+
config TEST_FPU
tristate "Test floating point operations in kernel space"
depends on X86 && !KCOV_INSTRUMENT_ALL
diff --git a/lib/Makefile b/lib/Makefile
index d4af75136c54..49a2a9e36224 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -101,6 +101,7 @@ obj-$(CONFIG_TEST_BLACKHOLE_DEV) += test_blackhole_dev.o
obj-$(CONFIG_TEST_MEMINIT) += test_meminit.o
obj-$(CONFIG_TEST_LOCKUP) += test_lockup.o
obj-$(CONFIG_TEST_HMM) += test_hmm.o
+obj-$(CONFIG_TEST_FREE_PAGES) += test_free_pages.o
#
# CFLAGS for compiling floating point code inside the kernel. x86/Makefile turns
diff --git a/lib/test_free_pages.c b/lib/test_free_pages.c
new file mode 100644
index 000000000000..074e76bd76b2
--- /dev/null
+++ b/lib/test_free_pages.c
@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * test_free_pages.c: Check that free_pages() doesn't leak memory
+ * Copyright (c) 2020 Oracle
+ * Author: Matthew Wilcox <willy@infradead.org>
+ */
+
+#include <linux/gfp.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+
+static void test_free_pages(gfp_t gfp)
+{
+ unsigned int i;
+
+ for (i = 0; i < 1000 * 1000; i++) {
+ unsigned long addr = __get_free_pages(gfp, 3);
+ struct page *page = virt_to_page(addr);
+
+ /* Simulate page cache getting a speculative reference */
+ get_page(page);
+ free_pages(addr, 3);
+ put_page(page);
+ }
+}
+
+static int m_in(void)
+{
+ test_free_pages(GFP_KERNEL);
+ test_free_pages(GFP_KERNEL | __GFP_COMP);
+
+ return 0;
+}
+
+static void m_ex(void)
+{
+}
+
+module_init(m_in);
+module_exit(m_ex);
+MODULE_AUTHOR("Matthew Wilcox <willy@infradead.org>");
+MODULE_LICENSE("GPL");
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6263a97e39c6..73e33ab6d249 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4952,6 +4952,9 @@ void __free_pages(struct page *page, unsigned int order)
{
if (put_page_testzero(page))
free_the_page(page, order);
+ else if (!PageHead(page))
+ while (order-- > 0)
+ free_the_page(page + (1 << order), order);
}
EXPORT_SYMBOL(__free_pages);