The patch titled
stop_machine: implement stop_machine_from_inactive_cpu()
has been added to the -mm tree. Its filename is
stop_machine-implement-stop_machine_from_inactive_cpu.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: stop_machine: implement stop_machine_from_inactive_cpu()
From: Tejun Heo <tj@xxxxxxxxxx>
Currently, mtrr wants stop_machine functionality while a CPU is being
brought up. As stop_machine() requires the calling CPU to be active, mtrr
implements its own stop_machine using stop_one_cpu() on each online CPU.
This doesn't only unnecessarily duplicate complex logic but also
introduces a possibility of deadlock when it races against the generic
stop_machine().
This patch implements stop_machine_from_inactive_cpu() to serve such use
cases. Its functionality is basically the same as stop_machine();
however, it should be called from a CPU which isn't active and doesn't
depend on working scheduling on the calling CPU.
This is achieved by using busy loops for synchronization and open-coding
stop_cpus queuing and waiting with direct invocation of fn() for local CPU
inbetween.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Suresh Siddha <suresh.b.siddha@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/stop_machine.h | 14 ++++++-
kernel/stop_machine.c | 62 ++++++++++++++++++++++++++++++++-
2 files changed, 73 insertions(+), 3 deletions(-)
diff -puN include/linux/stop_machine.h~stop_machine-implement-stop_machine_from_inactive_cpu include/linux/stop_machine.h
--- a/include/linux/stop_machine.h~stop_machine-implement-stop_machine_from_inactive_cpu
+++ a/include/linux/stop_machine.h
@@ -126,15 +126,19 @@ int stop_machine(int (*fn)(void *), void
*/
int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus);
+int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data,
+ const struct cpumask *cpus);
+
#else /* CONFIG_STOP_MACHINE && CONFIG_SMP */
static inline int __stop_machine(int (*fn)(void *), void *data,
const struct cpumask *cpus)
{
+ unsigned long flags;
int ret;
- local_irq_disable();
+ local_irq_save(flags);
ret = fn(data);
- local_irq_enable();
+ local_irq_restore(flags);
return ret;
}
@@ -144,5 +148,11 @@ static inline int stop_machine(int (*fn)
return __stop_machine(fn, data, cpus);
}
+static inline int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data,
+ const struct cpumask *cpus)
+{
+ return __stop_machine(fn, data, cpus);
+}
+
#endif /* CONFIG_STOP_MACHINE && CONFIG_SMP */
#endif /* _LINUX_STOP_MACHINE */
diff -puN kernel/stop_machine.c~stop_machine-implement-stop_machine_from_inactive_cpu kernel/stop_machine.c
--- a/kernel/stop_machine.c~stop_machine-implement-stop_machine_from_inactive_cpu
+++ a/kernel/stop_machine.c
@@ -439,8 +439,15 @@ static int stop_machine_cpu_stop(void *d
struct stop_machine_data *smdata = data;
enum stopmachine_state curstate = STOPMACHINE_NONE;
int cpu = smp_processor_id(), err = 0;
+ unsigned long flags;
bool is_active;
+ /*
+ * When called from stop_machine_from_inactive_cpu(), irq might
+ * already be disabled. Save the state and restore it on exit.
+ */
+ local_save_flags(flags);
+
if (!smdata->active_cpus)
is_active = cpu == cpumask_first(cpu_online_mask);
else
@@ -468,7 +475,7 @@ static int stop_machine_cpu_stop(void *d
}
} while (curstate != STOPMACHINE_EXIT);
- local_irq_enable();
+ local_irq_restore(flags);
return err;
}
@@ -495,4 +502,57 @@ int stop_machine(int (*fn)(void *), void
}
EXPORT_SYMBOL_GPL(stop_machine);
+/**
+ * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
+ * @fn: the function to run
+ * @data: the data ptr for the @fn()
+ * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
+ *
+ * This is identical to stop_machine() but can be called from a CPU which
+ * is not active. The local CPU is in the process of hotplug (so no other
+ * CPU hotplug can start) and not marked active and doesn't have enough
+ * context to sleep.
+ *
+ * This function provides stop_machine() functionality for such state by
+ * using busy-wait for synchronization and executing @fn directly for local
+ * CPU.
+ *
+ * CONTEXT:
+ * Local CPU is inactive. Temporarily stops all active CPUs.
+ *
+ * RETURNS:
+ * 0 if all executions of @fn returned 0, any non zero return value if any
+ * returned non zero.
+ */
+int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data,
+ const struct cpumask *cpus)
+{
+ struct stop_machine_data smdata = { .fn = fn, .data = data,
+ .active_cpus = cpus };
+ struct cpu_stop_done done;
+ int ret;
+
+ /* Local CPU must be inactive and CPU hotplug in progress. */
+ BUG_ON(cpu_active(raw_smp_processor_id()));
+ smdata.num_threads = num_active_cpus() + 1; /* +1 for local */
+
+ /* No proper task established and can't sleep - busy wait for lock. */
+ while (!mutex_trylock(&stop_cpus_mutex))
+ cpu_relax();
+
+ /* Schedule work on other CPUs and execute directly for local CPU */
+ set_state(&smdata, STOPMACHINE_PREPARE);
+ cpu_stop_init_done(&done, num_active_cpus());
+ queue_stop_cpus_work(cpu_active_mask, stop_machine_cpu_stop, &smdata,
+ &done);
+ ret = stop_machine_cpu_stop(&smdata);
+
+ /* Busy wait for completion. */
+ while (!completion_done(&done.completion))
+ cpu_relax();
+
+ mutex_unlock(&stop_cpus_mutex);
+ return ret ?: done.ret;
+}
+
#endif /* CONFIG_STOP_MACHINE */
_
Patches currently in -mm which might be from tj@xxxxxxxxxx are
linux-next.patch
x86-mtrr-lock-stop-machine-during-mtrr-rendezvous-sequence.patch
stop_machine-reorganize-stop_cpus-implementation.patch
stop_machine-implement-stop_machine_from_inactive_cpu.patch
x86-mtrr-use-stop_machine-apis-for-doing-mtrr-rendezvous.patch
drivers-use-kzalloc-kcalloc-instead-of-kmallocmemset-where-possible.patch
devres-fix-possible-use-after-free.patch
ptrace-unify-show_regs-prototype.patch
ptrace-unify-show_regs-prototype-fix.patch
scatterlist-new-helper-functions.patch
scatterlist-new-helper-functions-update.patch
scatterlist-new-helper-functions-update-fix.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
