Re: [patch] libitm: Fix handling of reentrancy in the HTM fastpath

[Peter Bergner]

On Wed, 2013-06-19 at 16:57 +0200, Torvald Riegel wrote:
> (Re-sending to the proper list. Sorry for the noise at gcc@.)
> 
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57643
> 
> The HTM fastpath didn't handle a situation in which a relaxed
> transaction executed unsafe code that in turn starts a transaction; it
> simply tried to wait for the "other" transaction, not checking whether
> the current thread started the other transaction.
[snip]
> Peter and/or Andreas: Could you please check that this fixes the bug you
> see on Power/s390?  Thanks.

This patch fixed the hang, but now I'm dying due to an abort in the
test case.  Specifically, the first abort in unsafe()

        int __attribute__((transaction_unsafe)) unsafe(int i)
         {
           if (_ITM_inTransaction() != inIrrevocableTransaction)
 dying here:  abort();
           __transaction_atomic {
             x++;
           }
           if (_ITM_inTransaction() != inIrrevocableTransaction)
             abort();
           return i+1;
         }

This is due to the following in _ITM_inTransaction():

47        if (tx && (tx->nesting > 0))
(gdb) p tx
$2 = (GTM::gtm_thread *) 0x10901bf0
(gdb) p tx->nesting
$3 = 1
(gdb) step
49            if (tx->state & gtm_thread::STATE_IRREVOCABLE)
(gdb) p tx->state
$4 = 3
(gdb) p gtm_thread::STATE_IRREVOCABLE
$5 = 2
(gdb) step
50              return inIrrevocableTransaction;

Peter