[Xen-devel] [PATCH RESEND 2/8] gnttab: avoid spurious maptrack handle allocation failures

["Jan Beulich" <JBeulich@xxxxxxxx>]

When no memory is available in the hypervisor, rather than immediately
failing the request, try to steal a handle from another vCPU.

Reported-by: George Dunlap <george.dunlap@xxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -411,7 +411,7 @@ get_maptrack_handle(
     struct vcpu          *curr = current;
     unsigned int          i, head;
     grant_handle_t        handle;
-    struct grant_mapping *new_mt;
+    struct grant_mapping *new_mt = NULL;
 
     handle = __get_maptrack_handle(lgt, curr);
     if ( likely(handle != -1) )
@@ -422,8 +422,13 @@ get_maptrack_handle(
     /*
      * If we've run out of frames, try stealing an entry from another
      * VCPU (in case the guest isn't mapping across its VCPUs evenly).
+     * Also use this path in case we're out of memory, to avoid spurious
+     * failures.
      */
-    if ( nr_maptrack_frames(lgt) >= max_maptrack_frames )
+    if ( nr_maptrack_frames(lgt) < max_maptrack_frames )
+        new_mt = alloc_xenheap_page();
+
+    if ( !new_mt )
     {
         spin_unlock(&lgt->maptrack_lock);
 
@@ -446,12 +451,6 @@ get_maptrack_handle(
         return steal_maptrack_handle(lgt, curr);
     }
 
-    new_mt = alloc_xenheap_page();
-    if ( !new_mt )
-    {
-        spin_unlock(&lgt->maptrack_lock);
-        return -1;
-    }
     clear_page(new_mt);
 
     /*




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