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["Kevin W. Rudd" <kevinr@xxxxxxxxxxxxxxxxxx>]

** Package changed: ubuntu => linux (Ubuntu)

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https://bugs.launchpad.net/bugs/1572624

Title:
  Backport patch to abort syscalls in active transactions

Status in linux package in Ubuntu:
  New

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;
          __transaction_atomic
          {
                  if(!stack_.empty())
                  {
                          ret = stack_.top();
                          stack_.pop();
                  } 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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