[Xen-changelog] [xen-unstable] x86/IRQ: fix create_irq() after c/s 24068:6928172f7ded

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User Jan Beulich <jbeulich@xxxxxxxx>
# Date 1320418550 -3600
# Node ID 659c800d7edf433c188917bf6faff177dd118c07
# Parent  974b00c7c2d070bcd3b107623f7cb3dff78cd79e
x86/IRQ: fix create_irq() after c/s 24068:6928172f7ded

init_one_irq_desc() must be called with interrupts enabled (as it may
call functions from the xmalloc() group). Rather than mis-using
vector_lock to also protect the finding of an unused IRQ, make this
lockless through using cmpxchg(), and obtain the lock only around the
actual assignment of the vector.

Also fold find_unassigned_irq() into its only caller.

It is, btw, questionable whether create_irq() calling
__assign_irq_vector() (rather than assign_irq_vector()) is actually
correct - desc->affinity appears to not get initialized properly in
this case.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Keir Fraser <keir@xxxxxxx>
---


diff -r 974b00c7c2d0 -r 659c800d7edf xen/arch/x86/irq.c
--- a/xen/arch/x86/irq.c        Fri Nov 04 14:24:07 2011 +0000
+++ b/xen/arch/x86/irq.c        Fri Nov 04 15:55:50 2011 +0100
@@ -151,16 +151,6 @@
     return ret;
 }
 
-static inline int find_unassigned_irq(void)
-{
-    int irq;
-
-    for (irq = nr_irqs_gsi; irq < nr_irqs; irq++)
-        if (irq_to_desc(irq)->arch.used == IRQ_UNUSED)
-            return irq;
-    return -ENOSPC;
-}
-
 /*
  * Dynamic irq allocate and deallocation for MSI
  */
@@ -170,19 +160,28 @@
     int irq, ret;
     struct irq_desc *desc;
 
-    spin_lock_irqsave(&vector_lock, flags);
+    for (irq = nr_irqs_gsi; irq < nr_irqs; irq++)
+    {
+        desc = irq_to_desc(irq);
+        if (cmpxchg(&desc->arch.used, IRQ_UNUSED, IRQ_RESERVED) == IRQ_UNUSED)
+           break;
+    }
 
-    irq = find_unassigned_irq();
-    if (irq < 0)
-         goto out;
-    desc = irq_to_desc(irq);
+    if (irq >= nr_irqs)
+         return -ENOSPC;
+
     ret = init_one_irq_desc(desc);
     if (!ret)
+    {
+        spin_lock_irqsave(&vector_lock, flags);
         ret = __assign_irq_vector(irq, desc, TARGET_CPUS);
+        spin_unlock_irqrestore(&vector_lock, flags);
+    }
     if (ret < 0)
+    {
+        desc->arch.used = IRQ_UNUSED;
         irq = ret;
-out:
-     spin_unlock_irqrestore(&vector_lock, flags);
+    }
 
     return irq;
 }
diff -r 974b00c7c2d0 -r 659c800d7edf xen/include/asm-x86/irq.h
--- a/xen/include/asm-x86/irq.h Fri Nov 04 14:24:07 2011 +0000
+++ b/xen/include/asm-x86/irq.h Fri Nov 04 15:55:50 2011 +0100
@@ -39,12 +39,13 @@
         unsigned move_cleanup_count;
         vmask_t *used_vectors;
         u8 move_in_progress : 1;
-        u8 used: 1;
+        s8 used;
 };
 
 /* For use with irq_cfg.used */
 #define IRQ_UNUSED      (0)
 #define IRQ_USED        (1)
+#define IRQ_RESERVED    (-1)
 
 #define IRQ_VECTOR_UNASSIGNED (-1)
 

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