x86, irq: Allow 0xff for /proc/irq/[n]/smp_affinity on an 8-cpu system

John Blackwood reported:
> on an older Dell PowerEdge 6650 system with 8 cpus (4 are hyper-threaded),
> and  32 bit (x86) kernel, once you change the irq smp_affinity of an irq
> to be less than all cpus in the system, you can never change really the
> irq smp_affinity back to be all cpus in the system (0xff) again,
> even though no error status is returned on the "/bin/echo ff >
> /proc/irq/[n]/smp_affinity" operation.
>
> This is due to that fact that BAD_APICID has the same value as
> all cpus (0xff) on 32bit kernels, and thus the value returned from
> set_desc_affinity() via the cpu_mask_to_apicid_and() function is treated
> as a failure in set_ioapic_affinity_irq_desc(), and no affinity changes
> are made.

set_desc_affinity() is already checking if the incoming cpu mask
intersects with the cpu online mask or not. So there is no need
for the apic op cpu_mask_to_apicid_and() to check again
and return BAD_APICID.

Remove the BAD_APICID return value from cpu_mask_to_apicid_and()
and also fix set_desc_affinity() to return -1 instead of using BAD_APICID
to represent error conditions (as cpu_mask_to_apicid_and() can return
logical or physical apicid values and BAD_APICID is really to represent
bad physical apic id).

Reported-by: John Blackwood <john.blackwood@ccur.com>
Root-caused-by: John Blackwood <john.blackwood@ccur.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
LKML-Reference: <1261103386.2535.409.camel@sbs-t61>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 14 insertions, 18 deletions

diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index d5d498fbee4b..98ced709e829 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -2276,26 +2276,28 @@ static void __target_IO_APIC_irq(unsigned int irq, unsigned int dest, struct irq
 
 /*
  * Either sets desc->affinity to a valid value, and returns
- * ->cpu_mask_to_apicid of that, or returns BAD_APICID and
+ * ->cpu_mask_to_apicid of that in dest_id, or returns -1 and
  * leaves desc->affinity untouched.
  */
 unsigned int
-set_desc_affinity(struct irq_desc *desc, const struct cpumask *mask)
+set_desc_affinity(struct irq_desc *desc, const struct cpumask *mask,
+                  unsigned int *dest_id)
 {
         struct irq_cfg *cfg;
         unsigned int irq;
 
         if (!cpumask_intersects(mask, cpu_online_mask))
-                return BAD_APICID;
+                return -1;
 
         irq = desc->irq;
         cfg = desc->chip_data;
         if (assign_irq_vector(irq, cfg, mask))
-                return BAD_APICID;
+                return -1;
 
         cpumask_copy(desc->affinity, mask);
 
-        return apic->cpu_mask_to_apicid_and(desc->affinity, cfg->domain);
+        *dest_id = apic->cpu_mask_to_apicid_and(desc->affinity, cfg->domain);
+        return 0;
 }
 
 static int
@@ -2311,12 +2313,11 @@ set_ioapic_affinity_irq_desc(struct irq_desc *desc, const struct cpumask *mask)
         cfg = desc->chip_data;
 
         spin_lock_irqsave(&ioapic_lock, flags);
-        dest = set_desc_affinity(desc, mask);
-        if (dest != BAD_APICID) {
+        ret = set_desc_affinity(desc, mask, &dest);
+        if (!ret) {
                 /* Only the high 8 bits are valid. */
                 dest = SET_APIC_LOGICAL_ID(dest);
                 __target_IO_APIC_irq(irq, dest, cfg);
-                ret = 0;
         }
         spin_unlock_irqrestore(&ioapic_lock, flags);
 
@@ -3351,8 +3352,7 @@ static int set_msi_irq_affinity(unsigned int irq, const struct cpumask *mask)
         struct msi_msg msg;
         unsigned int dest;
 
-        dest = set_desc_affinity(desc, mask);
-        if (dest == BAD_APICID)
+        if (set_desc_affinity(desc, mask, &dest))
                 return -1;
 
         cfg = desc->chip_data;
@@ -3384,8 +3384,7 @@ ir_set_msi_irq_affinity(unsigned int irq, const struct cpumask *mask)
         if (get_irte(irq, &irte))
                 return -1;
 
-        dest = set_desc_affinity(desc, mask);
-        if (dest == BAD_APICID)
+        if (set_desc_affinity(desc, mask, &dest))
                 return -1;
 
         irte.vector = cfg->vector;
@@ -3567,8 +3566,7 @@ static int dmar_msi_set_affinity(unsigned int irq, const struct cpumask *mask)
         struct msi_msg msg;
         unsigned int dest;
 
-        dest = set_desc_affinity(desc, mask);
-        if (dest == BAD_APICID)
+        if (set_desc_affinity(desc, mask, &dest))
                 return -1;
 
         cfg = desc->chip_data;
@@ -3623,8 +3621,7 @@ static int hpet_msi_set_affinity(unsigned int irq, const struct cpumask *mask)
         struct msi_msg msg;
         unsigned int dest;
 
-        dest = set_desc_affinity(desc, mask);
-        if (dest == BAD_APICID)
+        if (set_desc_affinity(desc, mask, &dest))
                 return -1;
 
         cfg = desc->chip_data;
@@ -3730,8 +3727,7 @@ static int set_ht_irq_affinity(unsigned int irq, const struct cpumask *mask)
         struct irq_cfg *cfg;
         unsigned int dest;
 
-        dest = set_desc_affinity(desc, mask);
-        if (dest == BAD_APICID)
+        if (set_desc_affinity(desc, mask, &dest))
                 return -1;
 
         cfg = desc->chip_data;