The required protection is that the caller cannot be migrated to a different CPU as these places take either a hash bucket lock or might trigger a kprobe inside the memory allocator. Both scenarios can lead to deadlocks. The deadlock prevention is per CPU by incrementing a per CPU variable which temporarily blocks the invocation of BPF programs from perf and kprobes. Replace the open coded preempt_disable/enable() and this_cpu_inc/dec() pairs with the new recursion prevention helpers to prepare BPF to work on PREEMPT_RT enabled kernels. On a non-RT kernel the migrate disable/enable in the helpers map to preempt_disable/enable(), i.e. no functional change. Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> --- V3: Use recursion prevention helpers consistently --- kernel/bpf/hashtab.c | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-) --- a/kernel/bpf/hashtab.c +++ b/kernel/bpf/hashtab.c @@ -1333,8 +1333,7 @@ static int } again: - preempt_disable(); - this_cpu_inc(bpf_prog_active); + bpf_disable_instrumentation(); rcu_read_lock(); again_nocopy: dst_key = keys; @@ -1362,8 +1361,7 @@ static int */ raw_spin_unlock_irqrestore(&b->lock, flags); rcu_read_unlock(); - this_cpu_dec(bpf_prog_active); - preempt_enable(); + bpf_enable_instrumentation(); goto after_loop; } @@ -1374,8 +1372,7 @@ static int */ raw_spin_unlock_irqrestore(&b->lock, flags); rcu_read_unlock(); - this_cpu_dec(bpf_prog_active); - preempt_enable(); + bpf_enable_instrumentation(); kvfree(keys); kvfree(values); goto alloc; @@ -1445,8 +1442,7 @@ static int } rcu_read_unlock(); - this_cpu_dec(bpf_prog_active); - preempt_enable(); + bpf_enable_instrumentation(); if (bucket_cnt && (copy_to_user(ukeys + total * key_size, keys, key_size * bucket_cnt) || copy_to_user(uvalues + total * value_size, values,
