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e320d3012d
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>
42 lines
829 B
C
42 lines
829 B
C
// SPDX-License-Identifier: GPL-2.0+
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/*
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* test_free_pages.c: Check that free_pages() doesn't leak memory
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* Copyright (c) 2020 Oracle
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* Author: Matthew Wilcox <willy@infradead.org>
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*/
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#include <linux/gfp.h>
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#include <linux/mm.h>
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#include <linux/module.h>
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static void test_free_pages(gfp_t gfp)
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{
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unsigned int i;
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for (i = 0; i < 1000 * 1000; i++) {
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unsigned long addr = __get_free_pages(gfp, 3);
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struct page *page = virt_to_page(addr);
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/* Simulate page cache getting a speculative reference */
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get_page(page);
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free_pages(addr, 3);
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put_page(page);
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}
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}
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static int m_in(void)
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{
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test_free_pages(GFP_KERNEL);
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test_free_pages(GFP_KERNEL | __GFP_COMP);
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return 0;
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}
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static void m_ex(void)
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{
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}
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module_init(m_in);
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module_exit(m_ex);
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MODULE_AUTHOR("Matthew Wilcox <willy@infradead.org>");
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MODULE_LICENSE("GPL");
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