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In PR122314 we noticed that our implementation of a barrier could execute tasks from the next "Task scheduling" region. This was because of a race condition where a barrier could be "completed", and some thread raced ahead to schedule another task on the "next" barrier all before some other thread checks for a bit on the generation number to tell if there is a task pending. The solution provided here is to check whether the generation number has "incremented" past the state that this barrier was entered with. As it happens the `state` variable already provided to `gomp_barrier_handle_tasks` is enough for the targets to tell whether the current global generation has incremented from the existing one. This requires some changes in the two loops in bar.c that are waiting on tasks being available. These loops now need to check for "generation has incremented" rather than "generation is identical to one increment forward". Without such an adjustment of the check a thread that is refusing to execute tasks because they have been scheduled for the next barrier will not continue into the next region until some other thread has completed the task (and removed the BAR_TASK_PENDING flag). This problem could be seen by a hang in testcases like task-reduction-13.c. Testing done: - Bootstrap & regtest on aarch64 and x86_64. - With & without _LIBGOMP_CHECKING_. - Testsuite with & without OMP_WAIT_POLICY=passive - Cross compilation & regtest on arm. - TSAN done on this as part of all my upstream patches. libgomp/ChangeLog: PR libgomp/122314 PR libgomp/88707 * config/gcn/bar.c (gomp_team_barrier_wait_end): Use gomp_barrier_state_is_incremented. (gomp_team_barrier_wait_cancel_end): Likewise. * config/gcn/bar.h (gomp_barrier_state_is_incremented, gomp_barrier_has_completed): New. * config/linux/bar.c (gomp_team_barrier_wait_end): Use gomp_barrier_state_is_incremented. (gomp_team_barrier_wait_cancel_end): Likewise. * config/linux/bar.h (gomp_barrier_state_is_incremented, gomp_barrier_has_completed): New. * config/nvptx/bar.h (gomp_barrier_state_is_incremented, gomp_barrier_has_completed): New. * config/posix/bar.c (gomp_team_barrier_wait_end): Use gomp_barrier_state_is_incremented. (gomp_team_barrier_wait_cancel_end): Likewise * config/posix/bar.h (gomp_barrier_state_is_incremented, gomp_barrier_has_completed): New. * config/rtems/bar.h (gomp_barrier_state_is_incremented, gomp_barrier_has_completed): New. * task.c (gomp_barrier_handle_tasks): Use gomp_barrier_has_completed. * testsuite/libgomp.c/pr122314.c: New test. Signed-off-by: Matthew Malcomson <mmalcomson@nvidia.com>
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