linux/lib/test_free_pages.c
Matthew Wilcox (Oracle) e320d3012d mm/page_alloc.c: fix freeing non-compound pages
Here is a very rare race which leaks memory:

Page P0 is allocated to the page cache.  Page P1 is free.

Thread A                Thread B                Thread C
find_get_entry():
xas_load() returns P0
						Removes P0 from page cache
						P0 finds its buddy P1
			alloc_pages(GFP_KERNEL, 1) returns P0
			P0 has refcount 1
page_cache_get_speculative(P0)
P0 has refcount 2
			__free_pages(P0)
			P0 has refcount 1
put_page(P0)
P1 is not freed

Fix this by freeing all the pages in __free_pages() that won't be freed
by the call to put_page().  It's usually not a good idea to split a page,
but this is a very unlikely scenario.

Fixes: e286781d5f ("mm: speculative page references")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nick Piggin <npiggin@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200926213919.26642-1-willy@infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-10-13 18:38:33 -07:00

43 lines
829 B
C

// 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");