This patch adds thread safety to the qemu_logfile handle.  This now
allows changing the logfile while logging is active, and also solves 
the issue of a seg fault while changing the logfile.

This patch adds use of RCU for handling the swap out of the 
old qemu_logfile file descriptor.

Also added a few tests for logfile including changing the logfile
and closing the logfile.

One change also added for a pre-existing double free issue in 
qemu_set_log_filename() uncovered with the new test.

We also cleaned up the flow of code in qemu_set_log().
---
v3
    - This version of the patch incorporates a few minor changes.
    - Change patch which adds qemu_logfile_mutex to remove the
      asserts that mutex is initialized, instead we will rely
      on the constructor.
    - Also added details to commit for patch adding mutex to explain some
      unavoidable temporary ugliness that we cleanup in a later patch. 
    - Change qemu_log_lock() to unconditionally hold the rcu_read_lock()
      until qemu_log_unlock().  
    - Also changed one use case in target/tilegx/translate.c
      to eliminate use of qemu_log_lock()/unlock().
---
v2
    - This version of the patch adds some cleanup of code in
      qemu_set_log().
    - Also changed the order of patches to move our fix for the
      double free issue in qemu_set_log_filename() up to the beginning
      of the patch.
---
v1
    - This version of the patch incorporates changes 
      from the first round of review.  
    - It also includes a fix for an issue in
      qemu_set_log_filename().  This issue was uncovered 
      by the test added for this patch.
---

Robert Foley (6):
  Fix double free issue in qemu_set_log_filename().
  Cleaned up flow of code in qemu_set_log(), to simplify and clarify.
  Add a mutex to guarantee single writer to qemu_logfile handle.
  qemu_log_lock/unlock now preserves the qemu_logfile handle.
  Add use of RCU for qemu_logfile.
  Added tests for close and change of logfile.

 accel/tcg/cpu-exec.c          |   4 +-
 accel/tcg/translate-all.c     |   4 +-
 accel/tcg/translator.c        |   4 +-
 exec.c                        |   4 +-
 hw/net/can/can_sja1000.c      |   4 +-
 include/exec/log.h            |  33 +++++++++--
 include/qemu/log.h            |  48 +++++++++++++---
 net/can/can_socketcan.c       |   5 +-
 target/cris/translate.c       |   4 +-
 target/i386/translate.c       |   5 +-
 target/lm32/translate.c       |   4 +-
 target/microblaze/translate.c |   4 +-
 target/nios2/translate.c      |   4 +-
 target/tilegx/translate.c     |   6 --
 target/unicore32/translate.c  |   4 +-
 tcg/tcg.c                     |  28 ++++++----
 tests/test-logging.c          |  80 +++++++++++++++++++++++++++
 util/log.c                    | 100 ++++++++++++++++++++++++++--------
 18 files changed, 268 insertions(+), 77 deletions(-)

-- 
2.17.1

Robert Foley <robert.foley@linaro.org> writes:

> This patch adds thread safety to the qemu_logfile handle.  This now
> allows changing the logfile while logging is active, and also solves
> the issue of a seg fault while changing the logfile.
>
> This patch adds use of RCU for handling the swap out of the
> old qemu_logfile file descriptor.
>
> Also added a few tests for logfile including changing the logfile
> and closing the logfile.
>
> One change also added for a pre-existing double free issue in
> qemu_set_log_filename() uncovered with the new test.
>
> We also cleaned up the flow of code in qemu_set_log().

This all looks good to me. As we are in hardfreeze now I think it's best
we wait for the tree to open before submitting the PR. If no one else
wants to pick this up I'll put together a PR.



> ---
> v3
>     - This version of the patch incorporates a few minor changes.
>     - Change patch which adds qemu_logfile_mutex to remove the
>       asserts that mutex is initialized, instead we will rely
>       on the constructor.
>     - Also added details to commit for patch adding mutex to explain some
>       unavoidable temporary ugliness that we cleanup in a later patch.
>     - Change qemu_log_lock() to unconditionally hold the rcu_read_lock()
>       until qemu_log_unlock().
>     - Also changed one use case in target/tilegx/translate.c
>       to eliminate use of qemu_log_lock()/unlock().
> ---
> v2
>     - This version of the patch adds some cleanup of code in
>       qemu_set_log().
>     - Also changed the order of patches to move our fix for the
>       double free issue in qemu_set_log_filename() up to the beginning
>       of the patch.
> ---
> v1
>     - This version of the patch incorporates changes
>       from the first round of review.
>     - It also includes a fix for an issue in
>       qemu_set_log_filename().  This issue was uncovered
>       by the test added for this patch.
> ---
>
> Robert Foley (6):
>   Fix double free issue in qemu_set_log_filename().
>   Cleaned up flow of code in qemu_set_log(), to simplify and clarify.
>   Add a mutex to guarantee single writer to qemu_logfile handle.
>   qemu_log_lock/unlock now preserves the qemu_logfile handle.
>   Add use of RCU for qemu_logfile.
>   Added tests for close and change of logfile.
>
>  accel/tcg/cpu-exec.c          |   4 +-
>  accel/tcg/translate-all.c     |   4 +-
>  accel/tcg/translator.c        |   4 +-
>  exec.c                        |   4 +-
>  hw/net/can/can_sja1000.c      |   4 +-
>  include/exec/log.h            |  33 +++++++++--
>  include/qemu/log.h            |  48 +++++++++++++---
>  net/can/can_socketcan.c       |   5 +-
>  target/cris/translate.c       |   4 +-
>  target/i386/translate.c       |   5 +-
>  target/lm32/translate.c       |   4 +-
>  target/microblaze/translate.c |   4 +-
>  target/nios2/translate.c      |   4 +-
>  target/tilegx/translate.c     |   6 --
>  target/unicore32/translate.c  |   4 +-
>  tcg/tcg.c                     |  28 ++++++----
>  tests/test-logging.c          |  80 +++++++++++++++++++++++++++
>  util/log.c                    | 100 ++++++++++++++++++++++++++--------
>  18 files changed, 268 insertions(+), 77 deletions(-)


--
Alex Bennée