From d809e134be7a1fdd9f5b99ab3291c6da5c0b8240 Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Wed, 14 Jul 2021 17:54:07 -0700 Subject: [PATCH] bpf: Prepare bpf_prog_put() to be called from irq context. MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Currently bpf_prog_put() is called from the task context only. With addition of bpf timers the timer related helpers will start calling bpf_prog_put() from irq-saved region and in rare cases might drop the refcnt to zero. To address this case, first, convert bpf_prog_free_id() to be irq-save (this is similar to bpf_map_free_id), and, second, defer non irq appropriate calls into work queue. For example: bpf_audit_prog() is calling kmalloc and wake_up_interruptible, bpf_prog_kallsyms_del_all()->bpf_ksym_del()->spin_unlock_bh(). They are not safe with irqs disabled. Signed-off-by: Alexei Starovoitov Signed-off-by: Daniel Borkmann Acked-by: Martin KaFai Lau Acked-by: Andrii Nakryiko Acked-by: Toke Høiland-Jørgensen Link: https://lore.kernel.org/bpf/20210715005417.78572-2-alexei.starovoitov@gmail.com --- kernel/bpf/syscall.c | 32 ++++++++++++++++++++++++++------ 1 file changed, 26 insertions(+), 6 deletions(-) diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index e343f15..5d1fee6 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -1699,6 +1699,8 @@ static int bpf_prog_alloc_id(struct bpf_prog *prog) void bpf_prog_free_id(struct bpf_prog *prog, bool do_idr_lock) { + unsigned long flags; + /* cBPF to eBPF migrations are currently not in the idr store. * Offloaded programs are removed from the store when their device * disappears - even if someone grabs an fd to them they are unusable, @@ -1708,7 +1710,7 @@ void bpf_prog_free_id(struct bpf_prog *prog, bool do_idr_lock) return; if (do_idr_lock) - spin_lock_bh(&prog_idr_lock); + spin_lock_irqsave(&prog_idr_lock, flags); else __acquire(&prog_idr_lock); @@ -1716,7 +1718,7 @@ void bpf_prog_free_id(struct bpf_prog *prog, bool do_idr_lock) prog->aux->id = 0; if (do_idr_lock) - spin_unlock_bh(&prog_idr_lock); + spin_unlock_irqrestore(&prog_idr_lock, flags); else __release(&prog_idr_lock); } @@ -1752,14 +1754,32 @@ static void __bpf_prog_put_noref(struct bpf_prog *prog, bool deferred) } } +static void bpf_prog_put_deferred(struct work_struct *work) +{ + struct bpf_prog_aux *aux; + struct bpf_prog *prog; + + aux = container_of(work, struct bpf_prog_aux, work); + prog = aux->prog; + perf_event_bpf_event(prog, PERF_BPF_EVENT_PROG_UNLOAD, 0); + bpf_audit_prog(prog, BPF_AUDIT_UNLOAD); + __bpf_prog_put_noref(prog, true); +} + static void __bpf_prog_put(struct bpf_prog *prog, bool do_idr_lock) { - if (atomic64_dec_and_test(&prog->aux->refcnt)) { - perf_event_bpf_event(prog, PERF_BPF_EVENT_PROG_UNLOAD, 0); - bpf_audit_prog(prog, BPF_AUDIT_UNLOAD); + struct bpf_prog_aux *aux = prog->aux; + + if (atomic64_dec_and_test(&aux->refcnt)) { /* bpf_prog_free_id() must be called first */ bpf_prog_free_id(prog, do_idr_lock); - __bpf_prog_put_noref(prog, true); + + if (in_irq() || irqs_disabled()) { + INIT_WORK(&aux->work, bpf_prog_put_deferred); + schedule_work(&aux->work); + } else { + bpf_prog_put_deferred(&aux->work); + } } } -- 2.7.4