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Commit | Line | Data |
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00e5a55c BS |
1 | References: 441793 |
2 | Subject: Cope with racy nature of sync_page in swap_sync_page | |
3 | ||
4 | From: NeilBrown <neilb@suse.de> | |
5 | ||
6 | sync_page is called without that PageLock held. This means that, | |
7 | for example, PageSwapCache can be cleared at any time. | |
8 | We need to be careful not to put much trust any any part of the page. | |
9 | ||
10 | So allow page_swap_info to return NULL of the page is no longer | |
11 | in a SwapCache, and handle the NULL gracefully in swap_sync_page. | |
12 | ||
13 | No other calls need to handle the NULL as that all hold PageLock, | |
14 | so PageSwapCache cannot be cleared by surprise. Add a WARN_ON to | |
15 | document this fact and help find out if I am wrong. | |
16 | ||
17 | Acked-By: Miklos Szeredi <mszeredi@novell.com> | |
18 | Signed-off-by: NeilBrown <neilb@suse.de> | |
19 | ||
20 | --- | |
21 | mm/page_io.c | 2 ++ | |
22 | mm/swapfile.c | 9 ++++++++- | |
23 | 2 files changed, 10 insertions(+), 1 deletion(-) | |
24 | ||
25 | --- linux-2.6.27.orig/mm/page_io.c | |
26 | +++ linux-2.6.27/mm/page_io.c | |
27 | @@ -139,6 +139,8 @@ void swap_sync_page(struct page *page) | |
28 | { | |
29 | struct swap_info_struct *sis = page_swap_info(page); | |
30 | ||
31 | + if (!sis) | |
32 | + return; | |
33 | if (sis->flags & SWP_FILE) { | |
34 | struct address_space *mapping = sis->swap_file->f_mapping; | |
35 | ||
36 | --- linux-2.6.27.orig/mm/swapfile.c | |
37 | +++ linux-2.6.27/mm/swapfile.c | |
38 | @@ -1845,7 +1845,13 @@ get_swap_info_struct(unsigned type) | |
39 | struct swap_info_struct *page_swap_info(struct page *page) | |
40 | { | |
41 | swp_entry_t swap = { .val = page_private(page) }; | |
42 | - BUG_ON(!PageSwapCache(page)); | |
43 | + if (!PageSwapCache(page) || !swap.val) { | |
44 | + /* This should only happen from sync_page. | |
45 | + * In other cases the page should be locked and | |
46 | + * should be in a SwapCache | |
47 | + */ | |
48 | + return NULL; | |
49 | + } | |
50 | return &swap_info[swp_type(swap)]; | |
51 | } | |
52 |