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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: davem@davemloft.net
Cc: daniel@iogearbox.net, andrii@kernel.org, netdev@vger.kernel.org,
	bpf@vger.kernel.org, kernel-team@fb.com
Subject: [PATCH v7 bpf-next 01/11] bpf: Prepare bpf_prog_put() to be called from irq context.
Date: Wed, 14 Jul 2021 17:54:07 -0700	[thread overview]
Message-ID: <20210715005417.78572-2-alexei.starovoitov@gmail.com> (raw)
In-Reply-To: <20210715005417.78572-1-alexei.starovoitov@gmail.com>

From: Alexei Starovoitov <ast@kernel.org>

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 <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
---
 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 e343f158e556..5d1fee634be8 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);
+		}
 	}
 }
 
-- 
2.30.2


  reply	other threads:[~2021-07-15  0:54 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-15  0:54 [PATCH v7 bpf-next 00/11] bpf: Introduce BPF timers Alexei Starovoitov
2021-07-15  0:54 ` Alexei Starovoitov [this message]
2021-07-15  0:54 ` [PATCH v7 bpf-next 02/11] bpf: Factor out bpf_spin_lock into helpers Alexei Starovoitov
2021-07-15  0:54 ` [PATCH v7 bpf-next 03/11] bpf: Introduce bpf timers Alexei Starovoitov
2021-07-15  0:54 ` [PATCH v7 bpf-next 04/11] bpf: Add map side support for " Alexei Starovoitov
2021-07-15  0:54 ` [PATCH v7 bpf-next 05/11] bpf: Prevent pointer mismatch in bpf_timer_init Alexei Starovoitov
2021-07-15  0:54 ` [PATCH v7 bpf-next 06/11] bpf: Remember BTF of inner maps Alexei Starovoitov
2021-07-15  0:54 ` [PATCH v7 bpf-next 07/11] bpf: Relax verifier recursion check Alexei Starovoitov
2021-07-15  0:54 ` [PATCH v7 bpf-next 08/11] bpf: Implement verifier support for validation of async callbacks Alexei Starovoitov
2022-01-04 17:15   ` Kris Van Hees
2022-01-04 18:19     ` Alexei Starovoitov
2021-07-15  0:54 ` [PATCH v7 bpf-next 09/11] bpf: Teach stack depth check about " Alexei Starovoitov
2021-07-15  0:54 ` [PATCH v7 bpf-next 10/11] selftests/bpf: Add bpf_timer test Alexei Starovoitov
2021-07-15  0:54 ` [PATCH v7 bpf-next 11/11] selftests/bpf: Add a test with bpf_timer in inner map Alexei Starovoitov
2021-07-15 20:40 ` [PATCH v7 bpf-next 00/11] bpf: Introduce BPF timers patchwork-bot+netdevbpf

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