On Wednesday, 12 of November 2008, Rusty Russell wrote:
> On Tuesday 11 November 2008 21:22:14 Ingo Molnar wrote:
> > * Rafael J. Wysocki <rjw@xxxxxxx> wrote:
> > > So, it evidently fails while re-enabling the non-boot CPU and not
> > > during disabling it as I thought before.
>
> (Resend, due to HTML version previously)
>
> But what is calling stop_machine in that path?
>
> There *is* a race, but I don't think it could cause this (we should make a
> copy of active.fnret inside the lock before returning it).
Still, that seems to be the case.
> Two patches: one fixes that race, the next adds debugging spew.
>
> stop_machine: fix race with return value
With this patch applied (reproduced below for clarity) the problem is not
reproducible any more.
Care to push it upstream ASAP?
Thanks,
Rafael
---
stop_machine: fix race with return value
We should not access active.fnret outside the lock; in theory the next
stop_machine could overwrite it.
Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
---
kernel/stop_machine.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff -r d7c9a15da615 kernel/stop_machine.c
--- a/kernel/stop_machine.c Mon Nov 10 09:47:45 2008 +1100
+++ b/kernel/stop_machine.c Tue Nov 11 23:19:47 2008 +1030
@@ -112,7 +112,7 @@
int __stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus)
{
struct work_struct *sm_work;
- int i;
+ int i, ret;
/* Set up initial state. */
mutex_lock(&lock);
@@ -137,8 +137,9 @@
/* This will release the thread on our CPU. */
put_cpu();
flush_workqueue(stop_machine_wq);
+ ret = active.fnret;
mutex_unlock(&lock);
- return active.fnret;
+ return ret;
}
int stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus)
--
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