[PATCH bpf-next v2 2/4] bpf: Use this_cpu_{inc_return|dec} for prog->active

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From: Hou Tao <houtao1@xxxxxxxxxx>

Both __this_cpu_inc_return() and __this_cpu_dec() are not preemption
safe and now migrate_disable() doesn't disable preemption, so the update
of prog-active is not atomic and in theory under fully preemptible kernel
recurisve prevention may do not work.

Fixing by using the preemption-safe and IRQ-safe variants.

Fixes: ca06f55b9002 ("bpf: Add per-program recursion prevention mechanism")
Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
---
 kernel/bpf/trampoline.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index ff87e38af8a7..ad76940b02cc 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -895,7 +895,7 @@ u64 notrace __bpf_prog_enter(struct bpf_prog *prog, struct bpf_tramp_run_ctx *ru
 
 	run_ctx->saved_run_ctx = bpf_set_run_ctx(&run_ctx->run_ctx);
 
-	if (unlikely(__this_cpu_inc_return(*(prog->active)) != 1)) {
+	if (unlikely(this_cpu_inc_return(*(prog->active)) != 1)) {
 		inc_misses_counter(prog);
 		return 0;
 	}
@@ -930,7 +930,7 @@ void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start, struct bpf_tramp_
 	bpf_reset_run_ctx(run_ctx->saved_run_ctx);
 
 	update_prog_stats(prog, start);
-	__this_cpu_dec(*(prog->active));
+	this_cpu_dec(*(prog->active));
 	migrate_enable();
 	rcu_read_unlock();
 }
@@ -966,7 +966,7 @@ u64 notrace __bpf_prog_enter_sleepable(struct bpf_prog *prog, struct bpf_tramp_r
 	migrate_disable();
 	might_fault();
 
-	if (unlikely(__this_cpu_inc_return(*(prog->active)) != 1)) {
+	if (unlikely(this_cpu_inc_return(*(prog->active)) != 1)) {
 		inc_misses_counter(prog);
 		return 0;
 	}
@@ -982,7 +982,7 @@ void notrace __bpf_prog_exit_sleepable(struct bpf_prog *prog, u64 start,
 	bpf_reset_run_ctx(run_ctx->saved_run_ctx);
 
 	update_prog_stats(prog, start);
-	__this_cpu_dec(*(prog->active));
+	this_cpu_dec(*(prog->active));
 	migrate_enable();
 	rcu_read_unlock_trace();
 }
-- 
2.29.2




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