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[Bug 1572624] Comment bridged from LTC Bugzilla


------- Comment From tulioqm@xxxxxxxxxx 2016-06-09 16:53 EDT-------

I suspect you're using the first version of the patch.
The last version is available in comment #2 and is called 0001-powerpc-tm-backport-b4b56f-to-Abort-syscalls-in-acti.patch

> This patch does not work for a 3.13 kernel.
> ubuntu-trusty/arch/powerpc/include/asm/tm.h: Assembler messages:
> ubuntu-trusty/arch/powerpc/include/asm/tm.h:11: Error: unrecognized opcode:
> `extern'

It seems that CONFIG_PPC_TRANSACTIONAL_MEM started to be defined.
Could you provide more context on this error message, please?

Wei, any suggestions how to proceed with this?

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  Backport patch to abort syscalls in active transactions

Status in linux package in Ubuntu:
  Fix Released
Status in linux source package in Trusty:
  Won't Fix
Status in linux source package in Vivid:
  Fix Committed
Status in linux source package in Wily:
  Fix Released
Status in linux source package in Xenial:
  Fix Released
Status in linux source package in Yakkety:
  Fix Released

Bug description:
  == Comment: #0 - Tulio Magno Quites Machado Filho - 2016-02-23 12:47:09 ==
  ---Problem Description---
  This is happening on Ubuntu 14.04.3.
  User is creating stack structure using C++ transactional memory extension:

      int Pop(int)
          int ret = 0;
                          ret = stack_.top();
                  } else
                          ret = -1;
          return ret;

  While evaluating if(!stack_.empty()), this code calls a libitm function (GCC code), which calls malloc (glibc code) which ends up calling futex (a syscall).
  A syscall inside a transaction is forbidden by the kernel, but there is nothing the user can do to avoid this syscall.

  This will hang the user application inside the malloc(), which would
  be waiting for the futex to return.

  Ubuntu 14.04 provides glibc 2.19, which is too old to know about HTM.
  And this is probably happening with other libraries as well.

  Backporting commit b4b56f9e would solve this issue.
  ---uname output---
  Linux 3.13.0-66-generic #108-Ubuntu SMP Wed Oct 7 16:06:09 UTC 2015 ppc64le ppc64le ppc64le GNU/Linux
  ---Steps to Reproduce---
   Start a transaction, make a syscall.
  == Comment: #1 - Wei Guo - 2016-02-24 02:33:03 ==
  I already verfied that kernel with patch b4b56f9e (on Ubuntu14.04) will work.

  == Comment: #2 - Wei Guo - 2016-02-26 04:20:37 ==
  Backport patch for commit b4b56f9e is attached. The patch is based on tag Ubuntu-lts-3.19.0-25.26_14.04.1.

  Tested based on Ubuntu 14.04.4 LTS ( 3.19.0-25-generic).

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