From: Jan Beulich <jbeulich@suse.com>
Date: Wed, 16 Aug 2017 08:56:23 +0000 (+0200)
Subject: gnttab: drop useless locking
X-Git-Tag: archive/raspbian/4.11.1-1+rpi1~1^2~66^2~1682
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=25726f4269c742fd41ee0df733bbe7a3a05339ac;p=xen.git

gnttab: drop useless locking

Holding any lock while accessing the maptrack entry fields is
pointless, as these entries are protected by their associated active
entry lock (which is being acquired later, before re-validating the
fields read without holding the lock).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
---

diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
index 56082d8373..5e578c69ff 100644
--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -1143,19 +1143,14 @@ __gnttab_unmap_common(
     smp_rmb();
     map = &maptrack_entry(lgt, op->handle);
 
-    grant_read_lock(lgt);
-
     if ( unlikely(!read_atomic(&map->flags)) )
     {
-        grant_read_unlock(lgt);
         gdprintk(XENLOG_INFO, "Zero flags for handle %#x\n", op->handle);
         op->status = GNTST_bad_handle;
         return;
     }
 
     dom = map->domid;
-    grant_read_unlock(lgt);
-
     if ( unlikely((rd = rcu_lock_domain_by_id(dom)) == NULL) )
     {
         /* This can happen when a grant is implicitly unmapped. */