On Wed, 2013-06-19 at 22:13 -0500, Peter Bergner wrote:
> On Thu, 2013-06-20 at 00:51 +0200, Torvald Riegel wrote:
> > On Wed, 2013-06-19 at 14:43 -0500, Peter Bergner wrote:
> > >> I'm having trouble seeing why/when _ITM_inTransaction() is
> > >> returning something other than inIrrevocableTransaction. I'll see if I
> > >> can
> > >> determine why and will report back.
> > >
> > > Ok, we return outsideTransaction because the nesting level (tx->nesting)
> > > is zero.
> >
> > That's a second bug in libitm, sorry. Can you try with the attached
> > patch additionally to the previous one? Thanks!
>
> Ok, with this patch, plus adding a powerpc implementation of
> htm_transaction_active(), reentrant.c now executes correctly
> on both HTM and non-HTM hardware for me. Thanks for all of
> your help with this!
>
> I'd still like to hear from Andreas, whether the reentrant.c test case
> with both patches, now works on S390.
>
> I'll note unlike your x86 htm_transaction_active() implementation,
> my implementation has to check for htm_available() first before
> executing the htm instruction which tells me whether I'm in transaction
> state or not, otherwise I'll get a SIGILL on non-HTM hardware.
> Unfortunately, my htm_available() call uses getauxval() to query
> the AUXV for a hwcap bit. Is there a place I can stash the result
> of the first call, so that subsequent calls use the cached value?
> Normally, I could use a static var, but I doubt that is what we want
> to do in static inline functions.
You're right, that was missing for x86 as well. Please see the updated
second patch that is attached. It additionally checks htm_fastpath to
see whether we are actually using the HTM. This variable is initialized
to the value that htm_init() returns. This should do the right thing I
suppose.
Torvald
commit c8352d4d9fa5cfa3453a61c581956835de9753e5
Author: Torvald Riegel <trie...@redhat.com>
Date: Thu Jun 20 00:46:59 2013 +0200
libitm: Handle HTM fastpath in status query functions.
diff --git a/libitm/config/x86/target.h b/libitm/config/x86/target.h
index 77b627f..063c09e 100644
--- a/libitm/config/x86/target.h
+++ b/libitm/config/x86/target.h
@@ -125,6 +125,13 @@ htm_abort_should_retry (uint32_t begin_ret)
{
return begin_ret & _XABORT_RETRY;
}
+
+/* Returns true iff a hardware transaction is currently being executed. */
+static inline bool
+htm_transaction_active ()
+{
+ return _xtest() != 0;
+}
#endif
diff --git a/libitm/query.cc b/libitm/query.cc
index 5707321..39a35b3 100644
--- a/libitm/query.cc
+++ b/libitm/query.cc
@@ -43,6 +43,15 @@ _ITM_libraryVersion (void)
_ITM_howExecuting ITM_REGPARM
_ITM_inTransaction (void)
{
+#if defined(USE_HTM_FASTPATH)
+ // If we use the HTM fastpath, we cannot reliably detect whether we are
+ // in a transaction because this function can be called outside of
+ // a transaction and thus we can't deduce this by looking at just the serial
+ // lock. This function isn't used in practice currently, so the easiest
+ // way to handle it is to just abort.
+ if (htm_fastpath && htm_transaction_active())
+ htm_abort();
+#endif
struct gtm_thread *tx = gtm_thr();
if (tx && (tx->nesting > 0))
{
@@ -58,6 +67,11 @@ _ITM_inTransaction (void)
_ITM_transactionId_t ITM_REGPARM
_ITM_getTransactionId (void)
{
+#if defined(USE_HTM_FASTPATH)
+ // See ITM_inTransaction.
+ if (htm_fastpath && htm_transaction_active())
+ htm_abort();
+#endif
struct gtm_thread *tx = gtm_thr();
return (tx && (tx->nesting > 0)) ? tx->id : _ITM_noTransactionId;
}
