xen/gnttab: add deferred freeing logic
Rather than just leaking pages that can't be freed at the point where access permission for the backend domain gets revoked, put them on a list and run a timer to (infrequently) retry freeing them. (This can particularly happen when unloading a frontend driver when devices are still present, and the backend still has them in non-closed state or hasn't finished closing them yet.) Signed-off-by: Jan Beulich <jbeulich@suse.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
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@ -426,10 +426,8 @@ static int gnttab_end_foreign_access_ref_v1(grant_ref_t ref, int readonly)
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nflags = *pflags;
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do {
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flags = nflags;
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if (flags & (GTF_reading|GTF_writing)) {
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printk(KERN_ALERT "WARNING: g.e. still in use!\n");
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if (flags & (GTF_reading|GTF_writing))
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return 0;
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}
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} while ((nflags = sync_cmpxchg(pflags, flags, 0)) != flags);
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return 1;
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@ -458,12 +456,103 @@ static int gnttab_end_foreign_access_ref_v2(grant_ref_t ref, int readonly)
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return 1;
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}
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int gnttab_end_foreign_access_ref(grant_ref_t ref, int readonly)
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static inline int _gnttab_end_foreign_access_ref(grant_ref_t ref, int readonly)
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{
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return gnttab_interface->end_foreign_access_ref(ref, readonly);
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}
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int gnttab_end_foreign_access_ref(grant_ref_t ref, int readonly)
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{
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if (_gnttab_end_foreign_access_ref(ref, readonly))
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return 1;
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pr_warn("WARNING: g.e. %#x still in use!\n", ref);
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return 0;
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}
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EXPORT_SYMBOL_GPL(gnttab_end_foreign_access_ref);
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struct deferred_entry {
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struct list_head list;
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grant_ref_t ref;
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bool ro;
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uint16_t warn_delay;
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struct page *page;
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};
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static LIST_HEAD(deferred_list);
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static void gnttab_handle_deferred(unsigned long);
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static DEFINE_TIMER(deferred_timer, gnttab_handle_deferred, 0, 0);
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static void gnttab_handle_deferred(unsigned long unused)
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{
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unsigned int nr = 10;
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struct deferred_entry *first = NULL;
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unsigned long flags;
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spin_lock_irqsave(&gnttab_list_lock, flags);
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while (nr--) {
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struct deferred_entry *entry
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= list_first_entry(&deferred_list,
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struct deferred_entry, list);
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if (entry == first)
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break;
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list_del(&entry->list);
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spin_unlock_irqrestore(&gnttab_list_lock, flags);
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if (_gnttab_end_foreign_access_ref(entry->ref, entry->ro)) {
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put_free_entry(entry->ref);
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if (entry->page) {
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pr_debug("freeing g.e. %#x (pfn %#lx)\n",
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entry->ref, page_to_pfn(entry->page));
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__free_page(entry->page);
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} else
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pr_info("freeing g.e. %#x\n", entry->ref);
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kfree(entry);
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entry = NULL;
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} else {
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if (!--entry->warn_delay)
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pr_info("g.e. %#x still pending\n",
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entry->ref);
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if (!first)
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first = entry;
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}
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spin_lock_irqsave(&gnttab_list_lock, flags);
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if (entry)
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list_add_tail(&entry->list, &deferred_list);
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else if (list_empty(&deferred_list))
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break;
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}
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if (!list_empty(&deferred_list) && !timer_pending(&deferred_timer)) {
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deferred_timer.expires = jiffies + HZ;
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add_timer(&deferred_timer);
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}
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spin_unlock_irqrestore(&gnttab_list_lock, flags);
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}
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static void gnttab_add_deferred(grant_ref_t ref, bool readonly,
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struct page *page)
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{
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struct deferred_entry *entry = kmalloc(sizeof(*entry), GFP_ATOMIC);
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const char *what = KERN_WARNING "leaking";
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if (entry) {
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unsigned long flags;
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entry->ref = ref;
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entry->ro = readonly;
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entry->page = page;
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entry->warn_delay = 60;
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spin_lock_irqsave(&gnttab_list_lock, flags);
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list_add_tail(&entry->list, &deferred_list);
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if (!timer_pending(&deferred_timer)) {
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deferred_timer.expires = jiffies + HZ;
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add_timer(&deferred_timer);
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}
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spin_unlock_irqrestore(&gnttab_list_lock, flags);
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what = KERN_DEBUG "deferring";
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}
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printk("%s g.e. %#x (pfn %#lx)\n",
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what, ref, page ? page_to_pfn(page) : -1);
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}
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void gnttab_end_foreign_access(grant_ref_t ref, int readonly,
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unsigned long page)
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{
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@ -471,12 +560,9 @@ void gnttab_end_foreign_access(grant_ref_t ref, int readonly,
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put_free_entry(ref);
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if (page != 0)
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free_page(page);
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} else {
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/* XXX This needs to be fixed so that the ref and page are
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placed on a list to be freed up later. */
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printk(KERN_WARNING
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"WARNING: leaking g.e. and page still in use!\n");
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}
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} else
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gnttab_add_deferred(ref, readonly,
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page ? virt_to_page(page) : NULL);
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}
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EXPORT_SYMBOL_GPL(gnttab_end_foreign_access);
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