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>
---
drivers/xen/grant-table.c | 106 +++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 96 insertions(+), 10 deletions(-)
--- 3.4-rc1/drivers/xen/grant-table.c
+++ 3.4-rc1-xen-gnttab-deferred-end-access/drivers/xen/grant-table.c
@@ -426,10 +426,8 @@ static int gnttab_end_foreign_access_ref
nflags = *pflags;
do {
flags = nflags;
- if (flags & (GTF_reading|GTF_writing)) {
- printk(KERN_ALERT "WARNING: g.e. still in use!\n");
+ if (flags & (GTF_reading|GTF_writing))
return 0;
- }
} while ((nflags = sync_cmpxchg(pflags, flags, 0)) != flags);
return 1;
@@ -458,12 +456,103 @@ static int gnttab_end_foreign_access_ref
return 1;
}
-int gnttab_end_foreign_access_ref(grant_ref_t ref, int readonly)
+static inline int _gnttab_end_foreign_access_ref(grant_ref_t ref, int readonly)
{
return gnttab_interface->end_foreign_access_ref(ref, readonly);
}
+
+int gnttab_end_foreign_access_ref(grant_ref_t ref, int readonly)
+{
+ if (_gnttab_end_foreign_access_ref(ref, readonly))
+ return 1;
+ pr_warn("WARNING: g.e. %#x still in use!\n", ref);
+ return 0;
+}
EXPORT_SYMBOL_GPL(gnttab_end_foreign_access_ref);
+struct deferred_entry {
+ struct list_head list;
+ grant_ref_t ref;
+ bool ro;
+ uint16_t warn_delay;
+ struct page *page;
+};
+static LIST_HEAD(deferred_list);
+static void gnttab_handle_deferred(unsigned long);
+static DEFINE_TIMER(deferred_timer, gnttab_handle_deferred, 0, 0);
+
+static void gnttab_handle_deferred(unsigned long unused)
+{
+ unsigned int nr = 10;
+ struct deferred_entry *first = NULL;
+ unsigned long flags;
+
+ spin_lock_irqsave(&gnttab_list_lock, flags);
+ while (nr--) {
+ struct deferred_entry *entry
+ = list_first_entry(&deferred_list,
+ struct deferred_entry, list);
+
+ if (entry == first)
+ break;
+ list_del(&entry->list);
+ spin_unlock_irqrestore(&gnttab_list_lock, flags);
+ if (_gnttab_end_foreign_access_ref(entry->ref, entry->ro)) {
+ put_free_entry(entry->ref);
+ if (entry->page) {
+ pr_debug("freeing g.e. %#x (pfn %#lx)\n",
+ entry->ref, page_to_pfn(entry->page));
+ __free_page(entry->page);
+ } else
+ pr_info("freeing g.e. %#x\n", entry->ref);
+ kfree(entry);
+ entry = NULL;
+ } else {
+ if (!--entry->warn_delay)
+ pr_info("g.e. %#x still pending\n",
+ entry->ref);
+ if (!first)
+ first = entry;
+ }
+ spin_lock_irqsave(&gnttab_list_lock, flags);
+ if (entry)
+ list_add_tail(&entry->list, &deferred_list);
+ else if (list_empty(&deferred_list))
+ break;
+ }
+ if (!list_empty(&deferred_list) &&
!timer_pending(&deferred_timer)) {
+ deferred_timer.expires = jiffies + HZ;
+ add_timer(&deferred_timer);
+ }
+ spin_unlock_irqrestore(&gnttab_list_lock, flags);
+}
+
+static void gnttab_add_deferred(grant_ref_t ref, bool readonly,
+ struct page *page)
+{
+ struct deferred_entry *entry = kmalloc(sizeof(*entry), GFP_ATOMIC);
+ const char *what = KERN_WARNING "leaking";
+
+ if (entry) {
+ unsigned long flags;
+
+ entry->ref = ref;
+ entry->ro = readonly;
+ entry->page = page;
+ entry->warn_delay = 60;
+ spin_lock_irqsave(&gnttab_list_lock, flags);
+ list_add_tail(&entry->list, &deferred_list);
+ if (!timer_pending(&deferred_timer)) {
+ deferred_timer.expires = jiffies + HZ;
+ add_timer(&deferred_timer);
+ }
+ spin_unlock_irqrestore(&gnttab_list_lock, flags);
+ what = KERN_DEBUG "deferring";
+ }
+ printk("%s g.e. %#x (pfn %#lx)\n",
+ what, ref, page ? page_to_pfn(page) : -1);
+}
+
void gnttab_end_foreign_access(grant_ref_t ref, int readonly,
unsigned long page)
{
@@ -471,12 +560,9 @@ void gnttab_end_foreign_access(grant_ref
put_free_entry(ref);
if (page != 0)
free_page(page);
- } else {
- /* XXX This needs to be fixed so that the ref and page are
- placed on a list to be freed up later. */
- printk(KERN_WARNING
- "WARNING: leaking g.e. and page still in use!\n");
- }
+ } else
+ gnttab_add_deferred(ref, readonly,
+ page ? virt_to_page(page) : NULL);
}
EXPORT_SYMBOL_GPL(gnttab_end_foreign_access);
