[SYCL] Fix unsafe usage of raw pointer to command in addHostAccessor

[KseniyaTikhomirova]

Command may be destroyed by cleanup process in another thread

Signed-off-by: Tikhomirova, Kseniya [email protected]

[bader]

@alexbatashev, how is it possible to have "build" directory in the image?

CMake configuration
  mkdir: cannot create directory 'build': File exists
  Error: Process completed with exit code 1.

https://github.com/intel/llvm/runs/5512042627?check_suite_focus=true

[cperkinsintel]

Is this premature exit the original problem?

[KseniyaTikhomirova]

no, original problem was that addHostAccessor (update requirement cmd and empty command creation) - the code under write lock here may be called by multiple threads (cmd1 for thread1 and command2 for thread2) and cmd1 may be removed from leaves and deleted under lock for cmd2 while code under read lock here that uses this raw pointer to cmd1 is not executed yet (enqueue is done but in in releaseHostAccessor in another thread that enqueue unblocked commands). In this case here we have not null but not valid pointer. So we receive - seg fault (rarely) or hang (frequently) because that memory block is reused for new cmd3 and is dependent on empty cmd for cmd1 that leads to closed dependency.

[cperkinsintel]

LGTM

[alexbatashev]

@alexbatashev, how is it possible to have "build" directory in the image?

CMake configuration
  mkdir: cannot create directory 'build': File exists
  Error: Process completed with exit code 1.

https://github.com/intel/llvm/runs/5512042627?check_suite_focus=true

The previous job that ran on this runner was terminated abnormally. Restart will help.

[bader]

@alexbatashev, how is it possible to have "build" directory in the image?

CMake configuration
  mkdir: cannot create directory 'build': File exists
  Error: Process completed with exit code 1.

https://github.com/intel/llvm/runs/5512042627?check_suite_focus=true

The previous job that ran on this runner was terminated abnormally. Restart will help.

I think we should handle this situation w/o restart.