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59 lines
1.8 KiB
59 lines
1.8 KiB
From: NeilBrown <neilb@suse.de>
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Subject: [PATCH 29/31] Cope with racy nature of sync_page in swap_sync_page
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Patch-mainline: not yet
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sync_page is called without that PageLock held. This means that,
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for example, PageSwapCache can be cleared at any time.
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We need to be careful not to put much trust any any part of the page.
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So allow page_swap_info to return NULL of the page is no longer
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in a SwapCache, and handle the NULL gracefully in swap_sync_page.
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No other calls need to handle the NULL as that all hold PageLock,
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so PageSwapCache cannot be cleared by surprise. Add a WARN_ON to
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document this fact and help find out if I am wrong.
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Acked-by: Miklos Szeredi <mszeredi@suse.cz>
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Signed-off-by: NeilBrown <neilb@suse.de>
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Signed-off-by: Suresh Jayaraman <sjayaraman@suse.de>
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---
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mm/page_io.c | 5 +++++
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mm/swapfile.c | 8 +++++++-
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2 files changed, 12 insertions(+), 1 deletion(-)
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--- a/mm/page_io.c
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+++ b/mm/page_io.c
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@@ -128,10 +128,15 @@ out:
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return ret;
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}
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+/* this comment ensure the patch applies to swap_sync_page
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+ * and not swap_set_page_dirty by mistake
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+ */
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void swap_sync_page(struct page *page)
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{
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struct swap_info_struct *sis = page_swap_info(page);
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+ if (!sis)
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+ return;
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if (sis->flags & SWP_FILE) {
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struct address_space *mapping = sis->swap_file->f_mapping;
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--- a/mm/swapfile.c
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+++ b/mm/swapfile.c
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@@ -2302,7 +2302,13 @@ int swapcache_prepare(swp_entry_t entry)
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struct swap_info_struct *page_swap_info(struct page *page)
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{
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swp_entry_t swap = { .val = page_private(page) };
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- BUG_ON(!PageSwapCache(page));
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+ if (!PageSwapCache(page) || !swap.val) {
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+ /* This should only happen from sync_page.
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+ * In other cases the page should be locked and
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+ * should be in a SwapCache
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+ */
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+ return NULL;
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+ }
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return swap_info[swp_type(swap)];
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}
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