Ls warn and stop nmi#11462
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While very unlikely, local storage theoretically may leak memory of the size of "struct bpf_local_storage" when destroy() fails to grab local_storage->lock and initializes selem->local_storage before other racing map_free() see it. Warn the user to allow debugging the issue instead of leaking the memory silently. Note that test_maps in bpf selftests already stress tested bpf_selem_unlink_nofail() by creating 4096 sockets and then immediately destroying them in multiple threads. With 64 threads, 64 x 4096 socket local storages were created and destroyed during the test and no warning in the function were triggered. Signed-off-by: Amery Hung <ameryhung@gmail.com>
Currently, local storage may deadlock when deferring freeing selem or local storage through kfree_rcu(), call_rcu() or call_rcu_tasks_trace() in NMI or reentrant. kfree_rcu() and call_rcu() have always been unsafe in NMI. call_rcu_tasks_trace() only became unsafe when it switched to call_srcu(). Since deleting selem in NMI is an unlikely use case, partially mitigate it by returning error when calling from bpf_xxx_storage_delete() helpers in NMI. The check is only added to bpf_selem_unlink(), which is used by helpers and syscalls. bpf_selem_unlink_nofail() is fine as it is called during map and owner tear down that never run in NMI or reentrant. The long-term solution requires _nolock versions of call_rcu. Another possible solution is to defer the free through irq_work, but it would grow the size of selem, which is non-ideal. Fixes: a10787e ("bpf: Enable task local storage for tracing programs") Signed-off-by: Amery Hung <ameryhung@gmail.com>
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