[patch v4 2/2] x86, mtrr: use __stop_machine() for doing MTRR rendezvous

Suresh Siddha
2011-06-13T18:01:09Z

[-- Attachment #1: use_stop_machine_for_mtrr_rendezvous.patch --]
[-- Type: text/plain, Size: 7633 bytes --]

MTRR rendezvous seqeuence using stop_one_cpu_nowait() can potentially
happen in parallel with another system wide rendezvous using
stop_machine(). This can lead to deadlock (The order in which
works are queued can be different on different cpu's. Some cpu's
will be running the first rendezvous handler and others will be running
the second rendezvous handler. Each set waiting for the other set to join
for the system wide rendezvous, leading to a deadlock).

MTRR rendezvous sequence is not implemened using stop_machine() before, as this
gets called both from the process context aswell as the cpu online paths
(where the cpu has not come online and the interrupts are disabled etc).

Now that __stop_machine() works even when the calling cpu is not online,
use __stop_machine() to implement the MTRR rendezvous sequence. This
will consolidate the code aswell as avoid the above mentioned deadlock.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: stable@kernel.org # v2.6.35+
---
arch/x86/kernel/cpu/mtrr/main.c | 154 +++++++---------------------------------
1 file changed, 27 insertions(+), 127 deletions(-)

Index: linux-2.6-tip/arch/x86/kernel/cpu/mtrr/main.c
===================================================================
--- linux-2.6-tip.orig/arch/x86/kernel/cpu/mtrr/main.c
+++ linux-2.6-tip/arch/x86/kernel/cpu/mtrr/main.c
@@ -137,18 +137,15 @@ static void __init init_table(void)
}

struct set_mtrr_data {
- atomic_t count;
- atomic_t gate;
unsigned long smp_base;
unsigned long smp_size;
unsigned int smp_reg;
mtrr_type smp_type;
};

-static DEFINE_PER_CPU(struct cpu_stop_work, mtrr_work);
-
/**
- * mtrr_work_handler - Synchronisation handler. Executed by "other" CPUs.
+ * mtrr_work_handler - Work done in the synchronisation handler. Executed by
+ * all the CPUs.
* @info: pointer to mtrr configuration data
*
* Returns nothing.
@@ -157,35 +154,26 @@ static int mtrr_work_handler(void *info)
{
#ifdef CONFIG_SMP
struct set_mtrr_data *data = info;
- unsigned long flags;
-
- atomic_dec(&data->count);
- while (!atomic_read(&data->gate))
- cpu_relax();
-
- local_irq_save(flags);

- atomic_dec(&data->count);
- while (atomic_read(&data->gate))
- cpu_relax();
-
- /* The master has cleared me to execute */
+ /*
+ * We use this same function to initialize the mtrrs during boot,
+ * resume, runtime cpu online and on an explicit request to set a
+ * specific MTRR.
+ *
+ * During boot or suspend, the state of the boot cpu's mtrrs has been
+ * saved, and we want to replicate that across all the cpus that come
+ * online (either at the end of boot or resume or during a runtime cpu
+ * online). If we're doing that, @reg is set to something special and on
+ * all the cpu's we do mtrr_if->set_all() (On the logical cpu that
+ * started the boot/resume sequence, this might be a duplicate
+ * set_all()).
+ */
if (data->smp_reg != ~0U) {
mtrr_if->set(data->smp_reg, data->smp_base,
data->smp_size, data->smp_type);
- } else if (mtrr_aps_delayed_init) {
- /*
- * Initialize the MTRRs inaddition to the synchronisation.
- */
+ } else if (mtrr_aps_delayed_init || !cpu_online(smp_processor_id())) {
mtrr_if->set_all();
}
-
- atomic_dec(&data->count);
- while (!atomic_read(&data->gate))
- cpu_relax();
-
- atomic_dec(&data->count);
- local_irq_restore(flags);
#endif
return 0;
}
@@ -223,20 +211,11 @@ static inline int types_compatible(mtrr_
* 14. Wait for buddies to catch up
* 15. Enable interrupts.
*
- * What does that mean for us? Well, first we set data.count to the number
- * of CPUs. As each CPU announces that it started the rendezvous handler by
- * decrementing the count, We reset data.count and set the data.gate flag
- * allowing all the cpu's to proceed with the work. As each cpu disables
- * interrupts, it'll decrement data.count once. We wait until it hits 0 and
- * proceed. We clear the data.gate flag and reset data.count. Meanwhile, they
- * are waiting for that flag to be cleared. Once it's cleared, each
- * CPU goes through the transition of updating MTRRs.
- * The CPU vendors may each do it differently,
- * so we call mtrr_if->set() callback and let them take care of it.
- * When they're done, they again decrement data->count and wait for data.gate
- * to be set.
- * When we finish, we wait for data.count to hit 0 and toggle the data.gate flag
- * Everyone then enables interrupts and we all continue on.
+ * What does that mean for us? Well, __stop_machine() will ensure that
+ * the rendezvous handler is started on each CPU. And in lockstep they
+ * do the state transition of disabling interrupts, updating MTRR's
+ * (the CPU vendors may each do it differently, so we call mtrr_if->set()
+ * callback and let them take care of it.) and enabling interrupts.
*
* Note that the mechanism is the same for UP systems, too; all the SMP stuff
* becomes nops.
@@ -244,92 +223,13 @@ static inline int types_compatible(mtrr_
static void
set_mtrr(unsigned int reg, unsigned long base, unsigned long size, mtrr_type type)
{
- struct set_mtrr_data data;
- unsigned long flags;
- int cpu;
-
- preempt_disable();
-
- data.smp_reg = reg;
- data.smp_base = base;
- data.smp_size = size;
- data.smp_type = type;
- atomic_set(&data.count, num_booting_cpus() - 1);
-
- /* Make sure data.count is visible before unleashing other CPUs */
- smp_wmb();
- atomic_set(&data.gate, 0);
-
- /* Start the ball rolling on other CPUs */
- for_each_online_cpu(cpu) {
- struct cpu_stop_work *work = &per_cpu(mtrr_work, cpu);
-
- if (cpu == smp_processor_id())
- continue;
-
- stop_one_cpu_nowait(cpu, mtrr_work_handler, &data, work);
- }
-
-
- while (atomic_read(&data.count))
- cpu_relax();
-
- /* Ok, reset count and toggle gate */
- atomic_set(&data.count, num_booting_cpus() - 1);
- smp_wmb();
- atomic_set(&data.gate, 1);
-
- local_irq_save(flags);
-
- while (atomic_read(&data.count))
- cpu_relax();
-
- /* Ok, reset count and toggle gate */
- atomic_set(&data.count, num_booting_cpus() - 1);
- smp_wmb();
- atomic_set(&data.gate, 0);
-
- /* Do our MTRR business */
-
- /*
- * HACK!
- *
- * We use this same function to initialize the mtrrs during boot,
- * resume, runtime cpu online and on an explicit request to set a
- * specific MTRR.
- *
- * During boot or suspend, the state of the boot cpu's mtrrs has been
- * saved, and we want to replicate that across all the cpus that come
- * online (either at the end of boot or resume or during a runtime cpu
- * online). If we're doing that, @reg is set to something special and on
- * this cpu we still do mtrr_if->set_all(). During boot/resume, this
- * is unnecessary if at this point we are still on the cpu that started
- * the boot/resume sequence. But there is no guarantee that we are still
- * on the same cpu. So we do mtrr_if->set_all() on this cpu aswell to be
- * sure that we are in sync with everyone else.
- */
- if (reg != ~0U)
- mtrr_if->set(reg, base, size, type);
- else
- mtrr_if->set_all();
-
- /* Wait for the others */
- while (atomic_read(&data.count))
- cpu_relax();
-
- atomic_set(&data.count, num_booting_cpus() - 1);
- smp_wmb();
- atomic_set(&data.gate, 1);
-
- /*
- * Wait here for everyone to have seen the gate change
- * So we're the last ones to touch 'data'
- */
- while (atomic_read(&data.count))
- cpu_relax();
+ struct set_mtrr_data data = { .smp_reg = reg,
+ .smp_base = base,
+ .smp_size = size,
+ .smp_type = type
+ };

- local_irq_restore(flags);
- preempt_enable();
+ __stop_machine(mtrr_work_handler, &data, cpu_callout_mask);
}

/**