On Mon, 17 Nov 2014, Thomas Gleixner wrote:
> On Mon, 17 Nov 2014, Linus Torvalds wrote:
> > llist_for_each_entry_safe(csd, csd_next, entry, llist) {
> > - csd->func(csd->info);
> > + smp_call_func_t func = csd->func;
> > + void *info = csd->info;
> > csd_unlock(csd);
> > +
> > + func(info);
>
> No, that won't work for synchronous calls:
>
> CPU 0 CPU 1
>
> csd_lock(csd);
> queue_csd();
> ipi();
> func = csd->func;
> info = csd->info;
> csd_unlock(csd);
> csd_lock_wait();
> func(info);
>
> The csd_lock_wait() side will succeed and therefor assume that the
> call has been completed while the function has not been called at
> all. Interesting explosions to follow.
>
> The proper solution is to revert that commit and properly analyze the
> problem which Jens was trying to solve and work from there.
So a combo of both (Jens and yours) might do the trick. Patch below.
I think what Jens was trying to solve is:
CPU 0 CPU 1
csd_lock(csd);
queue_csd();
ipi();
csd->func(csd->info);
wait_for_completion(csd);
complete(csd);
reuse_csd(csd);
csd_unlock(csd);
Thanks,
tglx
Index: linux/kernel/smp.c
===================================================================
--- linux.orig/kernel/smp.c
+++ linux/kernel/smp.c
@@ -126,7 +126,7 @@ static void csd_lock(struct call_single_
static void csd_unlock(struct call_single_data *csd)
{
- WARN_ON((csd->flags & CSD_FLAG_WAIT) && !(csd->flags & CSD_FLAG_LOCK));
+ WARN_ON(!(csd->flags & CSD_FLAG_LOCK));
/*
* ensure we're all done before releasing data:
@@ -250,8 +250,23 @@ static void flush_smp_call_function_queu
}
llist_for_each_entry_safe(csd, csd_next, entry, llist) {
- csd->func(csd->info);
- csd_unlock(csd);
+
+ /*
+ * For synchronous calls we are not allowed to unlock
+ * before the callback returned. For the async case
+ * its the responsibility of the caller to keep
+ * csd->info consistent while the callback runs.
+ */
+ if (csd->flags & CSD_FLAG_WAIT) {
+ csd->func(csd->info);
+ csd_unlock(csd);
+ } else {
+ smp_call_func_t func = csd->func;
+ void *info = csd->info;
+
+ csd_unlock(csd);
+ func(info);
+ }
}
/*
--
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