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xen/grant-table: Use put_page instead of free_page 

The page given to gnttab_end_foreign_access() to free could be a
compound page so use put_page() instead of free_page() since it can
handle both compound and single pages correctly.

This bug was discovered when migrating a Xen VM with several VIFs and
CONFIG_DEBUG_VM enabled. It hits a BUG usually after fewer than 10
iterations. All netfront devices disconnect from the backend during a
suspend/resume and this will call gnttab_end_foreign_access() if a
netfront queue has an outstanding skb. The mismatch between calling
get_page() and free_page() on a compound page causes a reference
counting error which is detected when DEBUG_VM is enabled.

Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
This commit is contained in:
Ross Lagerwall 2018-01-11 09:36:37 +00:00 committed by Juergen Gross
parent 4f277295e5
commit 3ac7292a25
1 changed files with 2 additions and 2 deletions
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4
drivers/xen/grant-table.c
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@ -382,7 +382,7 @@ static void gnttab_handle_deferred(struct timer_list *unused)
if (entry->page) { if (entry->page) {
pr_debug("freeing g.e. %#x (pfn %#lx)\n", pr_debug("freeing g.e. %#x (pfn %#lx)\n",
entry->ref, page_to_pfn(entry->page)); entry->ref, page_to_pfn(entry->page));
__free_page(entry->page); put_page(entry->page);
} else } else
pr_info("freeing g.e. %#x\n", entry->ref); pr_info("freeing g.e. %#x\n", entry->ref);
kfree(entry); kfree(entry);
@ -438,7 +438,7 @@ void gnttab_end_foreign_access(grant_ref_t ref, int readonly,
if (gnttab_end_foreign_access_ref(ref, readonly)) { if (gnttab_end_foreign_access_ref(ref, readonly)) {
put_free_entry(ref); put_free_entry(ref);
if (page != 0) if (page != 0)
free_page(page); put_page(virt_to_page(page));
} else } else
gnttab_add_deferred(ref, readonly, gnttab_add_deferred(ref, readonly,
page ? virt_to_page(page) : NULL); page ? virt_to_page(page) : NULL);