File 18661-recursive-spinlocks.patch of Package xen

Overview Repositories Revisions Requests Users Attributes Meta

File 18661-recursive-spinlocks.patch of Package xen

# HG changeset patch
# User Keir Fraser <keir.fraser@citrix.com>
# Date 1224519405 -3600
# Node ID 54d74fc0037ce688e79759ca632d3918f7aaa399
# Parent  f4dab783b58b41f2c67a66d6d095887faec3c296
spinlock: Modify recursive spinlock definitions to support up to 4095 CPUs.
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>

--- a/xen/include/asm-x86/spinlock.h
+++ b/xen/include/asm-x86/spinlock.h
@@ -8,11 +8,11 @@
 
 typedef struct {
     volatile s16 lock;
-    s8 recurse_cpu;
-    u8 recurse_cnt;
+    u16 recurse_cpu:12;
+    u16 recurse_cnt:4;
 } spinlock_t;
 
-#define SPIN_LOCK_UNLOCKED /*(spinlock_t)*/ { 1, -1, 0 }
+#define SPIN_LOCK_UNLOCKED { 1, 0xfffu, 0 }
 
 #define spin_lock_init(x)	do { *(x) = (spinlock_t) SPIN_LOCK_UNLOCKED; } while(0)
 #define spin_is_locked(x)	(*(volatile char *)(&(x)->lock) <= 0)
@@ -59,11 +59,15 @@ static inline int _raw_spin_trylock(spin
 #define _raw_spin_lock_recursive(_lock)            \
     do {                                           \
         int cpu = smp_processor_id();              \
+        /* Don't allow overflow of recurse_cpu field. */ \
+        BUILD_BUG_ON(NR_CPUS > 0xfffu);            \
         if ( likely((_lock)->recurse_cpu != cpu) ) \
         {                                          \
             spin_lock(_lock);                      \
             (_lock)->recurse_cpu = cpu;            \
         }                                          \
+        /* We support only fairly shallow recursion, else the counter overflows. */ \
+        ASSERT((_lock)->recurse_cnt < 0xfu);       \
         (_lock)->recurse_cnt++;                    \
     } while ( 0 )
 
@@ -71,7 +75,7 @@ static inline int _raw_spin_trylock(spin
     do {                                           \
         if ( likely(--(_lock)->recurse_cnt == 0) ) \
         {                                          \
-            (_lock)->recurse_cpu = -1;             \
+            (_lock)->recurse_cpu = 0xfffu;         \
             spin_unlock(_lock);                    \
         }                                          \
     } while ( 0 )

Places

File 18661-recursive-spinlocks.patch of Package xen

Places