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Date: Tue, 29 Sep 2020 12:59:42 +0200 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, stable@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, Alexei Starovoitov <ast@...nel.org>, Sasha Levin <sashal@...nel.org> Subject: [PATCH 4.14 070/166] bpf: Remove recursion prevention from rcu free callback From: Thomas Gleixner <tglx@...utronix.de> [ Upstream commit 8a37963c7ac9ecb7f86f8ebda020e3f8d6d7b8a0 ] If an element is freed via RCU then recursion into BPF instrumentation functions is not a concern. The element is already detached from the map and the RCU callback does not hold any locks on which a kprobe, perf event or tracepoint attached BPF program could deadlock. Signed-off-by: Thomas Gleixner <tglx@...utronix.de> Signed-off-by: Alexei Starovoitov <ast@...nel.org> Link: https://lore.kernel.org/bpf/20200224145643.259118710@linutronix.de Signed-off-by: Sasha Levin <sashal@...nel.org> --- kernel/bpf/hashtab.c | 8 -------- 1 file changed, 8 deletions(-) diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c index 6cc090d015f66..ecc58137525bc 100644 --- a/kernel/bpf/hashtab.c +++ b/kernel/bpf/hashtab.c @@ -645,15 +645,7 @@ static void htab_elem_free_rcu(struct rcu_head *head) struct htab_elem *l = container_of(head, struct htab_elem, rcu); struct bpf_htab *htab = l->htab; - /* must increment bpf_prog_active to avoid kprobe+bpf triggering while - * we're calling kfree, otherwise deadlock is possible if kprobes - * are placed somewhere inside of slub - */ - preempt_disable(); - __this_cpu_inc(bpf_prog_active); htab_elem_free(htab, l); - __this_cpu_dec(bpf_prog_active); - preempt_enable(); } static void htab_put_fd_value(struct bpf_htab *htab, struct htab_elem *l) -- 2.25.1
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