bpf: Use recursion prevention helpers in hashtab code

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@linutronix.de>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200224145644.211208533@linutronix.de

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 431cef2..ef83b01 100644 (file)
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -1333,8 +1333,7 @@ alloc:
        }
 
 again:
-       preempt_disable();
-       this_cpu_inc(bpf_prog_active);
+       bpf_disable_instrumentation();
        rcu_read_lock();
 again_nocopy:
        dst_key = keys;
@@ -1362,8 +1361,7 @@ again_nocopy:
                 */
                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 @@ again_nocopy:
                 */
                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 @@ next_batch:
        }
 
        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,