a862192e92
Prefetch work in mlx5_ib_prefetch_mr_work can be queued and able to run
concurrently with destruction of the implicit MR. The num_deferred_work
was intended to serialize this, but there is a race:
CPU0 CPU1
mlx5_ib_free_implicit_mr()
xa_erase(odp_mkeys)
synchronize_srcu()
__xa_erase(implicit_children)
mlx5_ib_prefetch_mr_work()
pagefault_mr()
pagefault_implicit_mr()
implicit_get_child_mr()
xa_cmpxchg()
atomic_dec_and_test(num_deferred_mr)
wait_event(imr->q_deferred_work)
ib_umem_odp_release(odp_imr)
kfree(odp_imr)
At this point in mlx5_ib_free_implicit_mr() the implicit_children list is
supposed to be empty forever so that destroy_unused_implicit_child_mr()
and related are not and will not be running.
Since it is not empty the destroy_unused_implicit_child_mr() flow ends up
touching deallocated memory as mlx5_ib_free_implicit_mr() already tore down the
imr parent.
The solution is to flush out the prefetch wq by driving num_deferred_work
to zero after creation of new prefetch work is blocked.
Fixes:
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| .. | ||
| core | ||
| hw | ||
| sw | ||
| ulp | ||
| Kconfig | ||
| Makefile | ||