From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7DE9920186 for ; Tue, 22 Aug 2023 19:46:47 +0000 (UTC) Received: from mail-pl1-x632.google.com (mail-pl1-x632.google.com [IPv6:2607:f8b0:4864:20::632]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 64995CCB for ; Tue, 22 Aug 2023 12:46:46 -0700 (PDT) Received: by mail-pl1-x632.google.com with SMTP id d9443c01a7336-1bc0d39b52cso32292495ad.2 for ; Tue, 22 Aug 2023 12:46:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20221208; t=1692733606; x=1693338406; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=mpUd4Xvv/qtthQLCrnM4XyQiw1F8WSpBmS6+o7vPpS0=; b=Am0OEo6geCDvXWXr4jXbYYjDBEEl+IGnfvWf9JdN6wyHzKXOp+AO6y+DLzvR21c9gH BXiJC2XGDAUIa4+TSxBjwNtu1EBde8lYmZcX3n4u+j8vGQ4bS4vB0Iltbcbp3ZImuShr hu/AmgY7+gL5JPEXfZ4+fFhepSrlpNRLVq4sVvEXDyiA9+WXxpas6rNWRytdzCxQwTuP 7+tVtBjyvxFt2s7fD/fQxQ+XMYX3EysMAaQGQKKZDB9sfapwOhr4ZPaSv8vQDR9kjTeu 0+ZH1sd86+5qwbgvJm321TzllU07ap0eWKOeClWu5VcRJZiwMrC5M3TfYDir8HFmclYz H/VA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1692733606; x=1693338406; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=mpUd4Xvv/qtthQLCrnM4XyQiw1F8WSpBmS6+o7vPpS0=; b=ew1A/sgEhuAL/znjEC+uCD4oNBd5C1XNB/kCt9JSjAQZAkJZnZSg1Gs6+H3s/8EQyL 2mmwKTcRevT+DPCUCk3KNXeoIBMY63wjrv3GJjr/a6YopQCDmpfKZcysIG58eizP0l3w HA03LG8aoyZvsHHvaTANWg5hypbRSrFh3Inyjb8qa1FYFKi3TNX1vmt4YSBhg6bqEQtC 2FZkUrN5aihOQNF15wq5ZCOt85Y3nzZbBVmBlDaMUgFgvt5zKadj3kh/Qq3TT0jjXWqW NDfX+VBnLbyUAV0fiswRhIm//1TmtHcA55BEa4HdZMWoKr1znxxNOanRvDOWKtmPri1K 7vDw== X-Gm-Message-State: AOJu0Yy15pq2YEPjViFJ8kO+u7N0VENecRNug9QddGr8nHPJUn6VIdzc kXijkWdqFE0HJlwK/LpyURSl32GHLjQ= X-Google-Smtp-Source: AGHT+IGvplrUEBZ81iw8Mwug+Zg+A7HBtFgHZgbpZTgPBJpjp/pcX0R3m73UM29nXsXRH/4rGUlKkA== X-Received: by 2002:a17:902:e5d2:b0:1bc:81f2:ddf0 with SMTP id u18-20020a170902e5d200b001bc81f2ddf0mr8949705plf.67.1692733605647; Tue, 22 Aug 2023 12:46:45 -0700 (PDT) Received: from MacBook-Pro-8.local ([2620:10d:c090:500::6:2150]) by smtp.gmail.com with ESMTPSA id y6-20020a17090322c600b001b8a3dd5a4asm9371831plg.283.2023.08.22.12.46.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Aug 2023 12:46:45 -0700 (PDT) Date: Tue, 22 Aug 2023 12:46:42 -0700 From: Alexei Starovoitov To: Yonghong Song Cc: Dave Marchevsky , bpf@vger.kernel.org, Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Kernel Team Subject: Re: [PATCH v2 bpf-next 6/7] bpf: Allow bpf_spin_{lock,unlock} in sleepable progs Message-ID: <20230822194642.rt4plvim7m77tlkh@MacBook-Pro-8.local> References: <20230821193311.3290257-1-davemarchevsky@fb.com> <20230821193311.3290257-7-davemarchevsky@fb.com> <3a24babf-c4e0-11a2-e4a7-3d14b8858d88@linux.dev> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3a24babf-c4e0-11a2-e4a7-3d14b8858d88@linux.dev> X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM, RCVD_IN_DNSWL_BLOCKED,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net On Mon, Aug 21, 2023 at 07:53:22PM -0700, Yonghong Song wrote: > > > On 8/21/23 12:33 PM, Dave Marchevsky wrote: > > Commit 9e7a4d9831e8 ("bpf: Allow LSM programs to use bpf spin locks") > > disabled bpf_spin_lock usage in sleepable progs, stating: > > > > Sleepable LSM programs can be preempted which means that allowng spin > > locks will need more work (disabling preemption and the verifier > > ensuring that no sleepable helpers are called when a spin lock is > > held). > > > > This patch disables preemption before grabbing bpf_spin_lock. The second > > requirement above "no sleepable helpers are called when a spin lock is > > held" is implicitly enforced by current verifier logic due to helper > > calls in spin_lock CS being disabled except for a few exceptions, none > > of which sleep. > > > > Due to above preemption changes, bpf_spin_lock CS can also be considered > > a RCU CS, so verifier's in_rcu_cs check is modified to account for this. > > > > Signed-off-by: Dave Marchevsky > > --- > > kernel/bpf/helpers.c | 2 ++ > > kernel/bpf/verifier.c | 9 +++------ > > 2 files changed, 5 insertions(+), 6 deletions(-) > > > > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c > > index 945a85e25ac5..8bd3812fb8df 100644 > > --- a/kernel/bpf/helpers.c > > +++ b/kernel/bpf/helpers.c > > @@ -286,6 +286,7 @@ static inline void __bpf_spin_lock(struct bpf_spin_lock *lock) > > compiletime_assert(u.val == 0, "__ARCH_SPIN_LOCK_UNLOCKED not 0"); > > BUILD_BUG_ON(sizeof(*l) != sizeof(__u32)); > > BUILD_BUG_ON(sizeof(*lock) != sizeof(__u32)); > > + preempt_disable(); > > arch_spin_lock(l); > > } > > @@ -294,6 +295,7 @@ static inline void __bpf_spin_unlock(struct bpf_spin_lock *lock) > > arch_spinlock_t *l = (void *)lock; > > arch_spin_unlock(l); > > + preempt_enable(); > > } > > preempt_disable()/preempt_enable() is not needed. Is it possible we can preempt_disable is needed in all cases. This mistake slipped in when we converted preempt disabled bpf progs into migrate disabled. For example, see how raw_spin_lock is doing it.