Re: BUG_ON(!cpus_equal(cpumask, tmp));

Andy Whitcroft
2004-04-01T11:37:47Z

--On 01 April 2004 10:34 +0530 Srivatsa Vaddagiri <vatsa@in.ibm.com> wrote:

> Hmm ..Doesn't it need to drop tlbstate_lock before returning?
> The second lock should be call_lock?

Yes and Yes. I don't know how Andrew copes with 300 odd patches.
I don't seem to be able to keep track of the versions on 3 of them?
Seems I sent out an old version. Doh. Explicit version numbers
from now on.

Below is tested version of the patch. If anyone can reproduce the
issue I would be interested in knowing if this passes a reboot on
that system.

Apologies for the confusion. And thanks for reviewing!

-apw

---
smp.c | 48 ++++++++++++++++++++++++++++++++++++++----------
1 files changed, 38 insertions(+), 10 deletions(-)

diff -upN reference/arch/i386/kernel/smp.c current/arch/i386/kernel/smp.c
--- reference/arch/i386/kernel/smp.c 2004-03-11 20:47:12.000000000 +0000
+++ current/arch/i386/kernel/smp.c 2004-04-01 12:35:40.000000000 +0100
@@ -355,8 +355,6 @@ static void flush_tlb_others(cpumask_t c
*/
BUG_ON(cpus_empty(cpumask));

- cpus_and(tmp, cpumask, cpu_online_map);
- BUG_ON(!cpus_equal(cpumask, tmp));
BUG_ON(cpu_isset(smp_processor_id(), cpumask));
BUG_ON(!mm);

@@ -367,16 +365,24 @@ static void flush_tlb_others(cpumask_t c
* detected by the NMI watchdog.
*/
spin_lock(&tlbstate_lock);
+
+ /* Subtle, mask the request mask with the currently online cpu's.
+ * Sample this under the lock; cpus in the the middle of going
+ * offline will wait until there is noone in this critical section
+ * before disabling IPI handling. */
+ cpus_and(tmp, cpumask, cpu_online_map);
+ if(cpus_empty(tmp))
+ goto out_unlock;

flush_mm = mm;
flush_va = va;
#if NR_CPUS <= BITS_PER_LONG
- atomic_set_mask(cpumask, &flush_cpumask);
+ atomic_set_mask(tmp, &flush_cpumask);
#else
{
int k;
unsigned long *flush_mask = (unsigned long *)&flush_cpumask;
- unsigned long *cpu_mask = (unsigned long *)&cpumask;
+ unsigned long *cpu_mask = (unsigned long *)&tmp;
for (k = 0; k < BITS_TO_LONGS(NR_CPUS); ++k)
atomic_set_mask(cpu_mask[k], &flush_mask[k]);
}
@@ -385,7 +391,7 @@ static void flush_tlb_others(cpumask_t c
* We have to send the IPI only to
* CPUs affected.
*/
- send_IPI_mask(cpumask, INVALIDATE_TLB_VECTOR);
+ send_IPI_mask(tmp, INVALIDATE_TLB_VECTOR);

while (!cpus_empty(flush_cpumask))
/* nothing. lockup detection does not belong here */
@@ -393,6 +399,7 @@ static void flush_tlb_others(cpumask_t c

flush_mm = NULL;
flush_va = 0;
+out_unlock:
spin_unlock(&tlbstate_lock);
}

@@ -514,11 +521,8 @@ int smp_call_function (void (*func) (voi
*/
{
struct call_data_struct data;
- int cpus = num_online_cpus()-1;
-
- if (!cpus)
- return 0;
-
+ int cpus;
+
data.func = func;
data.info = info;
atomic_set(&data.started, 0);
@@ -527,6 +531,15 @@ int smp_call_function (void (*func) (voi
atomic_set(&data.finished, 0);

spin_lock(&call_lock);
+
+ /* Subtle, get the current number of online cpus.
+ * Sample this under the lock; cpus in the the middle of going
+ * offline will wait until there is noone in this critical section
+ * before disabling IPI handling. */
+ cpus = num_online_cpus()-1;
+ if (!cpus)
+ goto out_unlock;
+
call_data = &data;
mb();

@@ -540,6 +553,7 @@ int smp_call_function (void (*func) (voi
if (wait)
while (atomic_read(&data.finished) != cpus)
barrier();
+out_unlock:
spin_unlock(&call_lock);

return 0;
@@ -551,6 +565,20 @@ static void stop_this_cpu (void * dummy)
* Remove this CPU:
*/
cpu_clear(smp_processor_id(), cpu_online_map);
+
+ /* Subtle, IPI users assume that they will be able to get IPI's
+ * though to the cpus listed in cpu_online_map. To ensure this
+ * we add the requirement that they check cpu_online_map within
+ * the IPI critical sections. Here we remove ourselves from the
+ * map, then ensure that all other cpus have left the relevant
+ * critical sections since the change. We do this by aquiring
+ * the relevant section locks, if we have them none else is in
+ * them. Once this is done we can go offline. */
+ spin_lock(&tlbstate_lock);
+ spin_unlock(&tlbstate_lock);
+ spin_lock(&call_lock);
+ spin_unlock(&call_lock);
+
local_irq_disable();
disable_local_APIC();
if (cpu_data[smp_processor_id()].hlt_works_ok)