Commit 085fee1a authored Feb 24, 2020 by Thomas Gleixner Committed by Alexei Starovoitov Feb 24, 2020

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

parent c518cfa0

kernel/bpf/hashtab.c

+4 −8

Original line number	Diff line number	Diff line
		@@ -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,

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