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bpf: Remove recursion prevention from rcu free callback 

[ Upstream commit 8a37963c7a ]

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@linutronix.de>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200224145643.259118710@linutronix.de
Signed-off-by: Sasha Levin <sashal@kernel.org>
5.4-rM2-2.2.x-imx-squashed
Thomas Gleixner 2020-02-24 15:01:39 +01:00 committed by Greg Kroah-Hartman
parent e8b95c29cd
commit f60007c9e9
1 changed files with 0 additions and 8 deletions
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8
kernel/bpf/hashtab.c
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@ -664,15 +664,7 @@ 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)