co_queue_wakeup is currently implemented in a recursive fashion.  Pathological
patterns of aio_co_enter() between coroutines can cause stack exhaustion.

This patch series implements co_queue_wakeup iteratively and avoids stack
exhaustion.

This issue was originally reported with qemu-img convert but I don't have a
good reproducer.  See Patch 3 for a test-aio test case instead.

Stefan Hajnoczi (3):
  queue: add QSIMPLEQ_PREPEND()
  coroutine: avoid co_queue_wakeup recursion
  coroutine: add test-aio coroutine queue chaining test case

 include/qemu/coroutine_int.h |   1 -
 include/qemu/queue.h         |   8 ++++
 block/io.c                   |   3 +-
 tests/test-aio.c             |  65 ++++++++++++++++++++-----
 util/qemu-coroutine-lock.c   |  34 -------------
 util/qemu-coroutine.c        | 110 +++++++++++++++++++++++--------------------
 6 files changed, 120 insertions(+), 101 deletions(-)

-- 
2.14.3

On 22/03/2018 16:28, Stefan Hajnoczi wrote:
> co_queue_wakeup is currently implemented in a recursive fashion.  Pathological
> patterns of aio_co_enter() between coroutines can cause stack exhaustion.
> 
> This patch series implements co_queue_wakeup iteratively and avoids stack
> exhaustion.
> 
> This issue was originally reported with qemu-img convert but I don't have a
> good reproducer.  See Patch 3 for a test-aio test case instead.
> 
> Stefan Hajnoczi (3):
>   queue: add QSIMPLEQ_PREPEND()
>   coroutine: avoid co_queue_wakeup recursion
>   coroutine: add test-aio coroutine queue chaining test case
> 
>  include/qemu/coroutine_int.h |   1 -
>  include/qemu/queue.h         |   8 ++++
>  block/io.c                   |   3 +-
>  tests/test-aio.c             |  65 ++++++++++++++++++++-----
>  util/qemu-coroutine-lock.c   |  34 -------------
>  util/qemu-coroutine.c        | 110 +++++++++++++++++++++++--------------------
>  6 files changed, 120 insertions(+), 101 deletions(-)
> 

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

I was a little surprised by the disappearing of the "do not use co
anymore" comments, but they seem unnecessary indeed with the new code.

Paolo

On Thu, Mar 22, 2018 at 03:28:31PM +0000, Stefan Hajnoczi wrote:
> co_queue_wakeup is currently implemented in a recursive fashion.  Pathological
> patterns of aio_co_enter() between coroutines can cause stack exhaustion.
> 
> This patch series implements co_queue_wakeup iteratively and avoids stack
> exhaustion.
> 
> This issue was originally reported with qemu-img convert but I don't have a
> good reproducer.  See Patch 3 for a test-aio test case instead.
> 
> Stefan Hajnoczi (3):
>   queue: add QSIMPLEQ_PREPEND()
>   coroutine: avoid co_queue_wakeup recursion
>   coroutine: add test-aio coroutine queue chaining test case
> 
>  include/qemu/coroutine_int.h |   1 -
>  include/qemu/queue.h         |   8 ++++
>  block/io.c                   |   3 +-
>  tests/test-aio.c             |  65 ++++++++++++++++++++-----
>  util/qemu-coroutine-lock.c   |  34 -------------
>  util/qemu-coroutine.c        | 110 +++++++++++++++++++++++--------------------
>  6 files changed, 120 insertions(+), 101 deletions(-)
> 
> -- 
> 2.14.3
> 

Thanks, applied to my block tree:
https://github.com/stefanha/qemu/commits/block

Stefan