[Xen-devel] [PATCH RFC 6/8] spinlock: Introduce _spin_lock_cond()

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

Because _spin_trylock() doesn't take lock ticket it may take a
long time until the lock is taken.

Add _spin_lock_cond() that waits for the lock while periodically
checking condition that may cause the lock request to be dropped.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---
 xen/common/spinlock.c      |   25 +++++++++++++++++++++++++
 xen/include/xen/spinlock.h |    3 +++
 2 files changed, 28 insertions(+), 0 deletions(-)

diff --git a/xen/common/spinlock.c b/xen/common/spinlock.c
index 2a06406..4fd46e5 100644
--- a/xen/common/spinlock.c
+++ b/xen/common/spinlock.c
@@ -129,6 +129,31 @@ static always_inline u16 observe_head(spinlock_tickets_t 
*t)
     return read_atomic(&t->head);
 }
 
+int _spin_lock_cond(spinlock_t *lock, bool_t (*cond)(void *), void *data)
+{
+    spinlock_tickets_t tickets = SPINLOCK_TICKET_INC;
+    LOCK_PROFILE_VAR;
+
+    check_lock(&lock->debug);
+    tickets.head_tail = arch_fetch_and_add(&lock->tickets.head_tail,
+                                           tickets.head_tail);
+    while ( tickets.tail != observe_head(&lock->tickets) )
+    {
+        LOCK_PROFILE_BLOCK;
+        arch_lock_relax();
+        if ( cond && !cond(data) )
+        {
+            add_sized(&lock->tickets.head, 1);
+            arch_lock_signal();
+            return 0;
+        }
+    }
+    LOCK_PROFILE_GOT;
+    preempt_disable();
+    arch_lock_acquire_barrier();
+    return 1;
+}
+
 void _spin_lock(spinlock_t *lock)
 {
     spinlock_tickets_t tickets = SPINLOCK_TICKET_INC;
diff --git a/xen/include/xen/spinlock.h b/xen/include/xen/spinlock.h
index c1883bd..b8bf72a 100644
--- a/xen/include/xen/spinlock.h
+++ b/xen/include/xen/spinlock.h
@@ -153,6 +153,7 @@ typedef struct spinlock {
 #define spin_lock_init(l) (*(l) = (spinlock_t)SPIN_LOCK_UNLOCKED)
 
 void _spin_lock(spinlock_t *lock);
+int _spin_lock_cond(spinlock_t *lock, bool_t (*cond)(void *), void *data);
 void _spin_lock_irq(spinlock_t *lock);
 unsigned long _spin_lock_irqsave(spinlock_t *lock);
 
@@ -169,6 +170,8 @@ void _spin_lock_recursive(spinlock_t *lock);
 void _spin_unlock_recursive(spinlock_t *lock);
 
 #define spin_lock(l)                  _spin_lock(l)
+#define spin_lock_cond(l, c, d)       _spin_lock_cond(l, c, d)
+#define spink_lock_kick(l)            arch_lock_signal()
 #define spin_lock_irq(l)              _spin_lock_irq(l)
 #define spin_lock_irqsave(l, f)                                 \
     ({                                                          \
-- 
1.7.1


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