[Xen-devel] [PATCH 6/6] x86/smt: Don't use -EBUSY for smt_up_down_helper() continuations

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Tasklet context is now capable of using handling continuations.  Use this
rather than -EBUSY as it is a more efficient way to restart the hypercall.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/sysctl.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/sysctl.c b/xen/arch/x86/sysctl.c
index 4a76f0f47f..06955fdc3e 100644
--- a/xen/arch/x86/sysctl.c
+++ b/xen/arch/x86/sysctl.c
@@ -85,6 +85,9 @@ long cpu_up_helper(void *data)
         /* On EBUSY, flush RCU work and have one more go. */
         rcu_barrier();
         ret = cpu_up(cpu);
+
+        if ( ret == -EBUSY )
+            ret = -ERESTART;
     }
 
     if ( !ret && !opt_smt &&
@@ -110,6 +113,9 @@ long cpu_down_helper(void *data)
         /* On EBUSY, flush RCU work and have one more go. */
         rcu_barrier();
         ret = cpu_down(cpu);
+
+        if ( ret == -EBUSY )
+            ret = -ERESTART;
     }
     return ret;
 }
@@ -143,8 +149,7 @@ static long smt_up_down_helper(void *data)
          */
         if ( ret != -EEXIST && general_preempt_check() )
         {
-            /* In tasklet context - can't create a contination. */
-            ret = -EBUSY;
+            ret = -ERESTART;
             break;
         }
 
-- 
2.11.0


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