From patchwork Thu Oct 5 06:31:52 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Song Liu X-Patchwork-Id: 13410036 X-Patchwork-Delegate: bpf@iogearbox.net 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 1CBD725119 for ; Thu, 5 Oct 2023 13:52:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=none Received: from mx0a-00082601.pphosted.com (mx0b-00082601.pphosted.com [67.231.153.30]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DD2B6469B for ; Thu, 5 Oct 2023 06:52:03 -0700 (PDT) Received: from pps.filterd (m0089730.ppops.net [127.0.0.1]) by m0089730.ppops.net (8.17.1.19/8.17.1.19) with ESMTP id 395318KG004297 for ; Wed, 4 Oct 2023 23:32:02 -0700 Received: from maileast.thefacebook.com ([163.114.130.16]) by m0089730.ppops.net (PPS) with ESMTPS id 3thmv4s7w2-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Wed, 04 Oct 2023 23:32:01 -0700 Received: from twshared19681.14.frc2.facebook.com (2620:10d:c0a8:1c::11) by mail.thefacebook.com (2620:10d:c0a8:82::b) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.23; Wed, 4 Oct 2023 23:32:01 -0700 Received: by devbig932.frc1.facebook.com (Postfix, from userid 4523) id 0B213257863C4; Wed, 4 Oct 2023 23:31:54 -0700 (PDT) From: Song Liu To: CC: , , , , , Song Liu , Tejun Heo Subject: [PATCH v3 bpf-next] bpf: Avoid unnecessary -EBUSY from htab_lock_bucket Date: Wed, 4 Oct 2023 23:31:52 -0700 Message-ID: <20231005063152.3205800-1-song@kernel.org> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-FB-Internal: Safe X-Proofpoint-GUID: GZYTZUNP-H9g7lwQIfiiD5cqx_e1XR0_ X-Proofpoint-ORIG-GUID: GZYTZUNP-H9g7lwQIfiiD5cqx_e1XR0_ X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.267,Aquarius:18.0.980,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2023-10-05_03,2023-10-02_01,2023-05-22_02 X-Spam-Status: No, score=-1.6 required=5.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_BLOCKED,RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net X-Patchwork-Delegate: bpf@iogearbox.net htab_lock_bucket uses the following logic to avoid recursion: 1. preempt_disable(); 2. check percpu counter htab->map_locked[hash] for recursion; 2.1. if map_lock[hash] is already taken, return -BUSY; 3. raw_spin_lock_irqsave(); However, if an IRQ hits between 2 and 3, BPF programs attached to the IRQ logic will not able to access the same hash of the hashtab and get -EBUSY. This -EBUSY is not really necessary. Fix it by disabling IRQ before checking map_locked: 1. preempt_disable(); 2. local_irq_save(); 3. check percpu counter htab->map_locked[hash] for recursion; 3.1. if map_lock[hash] is already taken, return -BUSY; 4. raw_spin_lock(). Similarly, use raw_spin_unlock() and local_irq_restore() in htab_unlock_bucket(). Suggested-by: Tejun Heo Signed-off-by: Song Liu --- Changes in v3: 1. Use raw_local_irq_* APIs instead. Changes in v2: 1. Use raw_spin_unlock() and local_irq_restore() in htab_unlock_bucket(). (Andrii) --- kernel/bpf/hashtab.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c index a8c7e1c5abfa..74c8d1b41dd5 100644 --- a/kernel/bpf/hashtab.c +++ b/kernel/bpf/hashtab.c @@ -155,13 +155,15 @@ static inline int htab_lock_bucket(const struct bpf_htab *htab, hash = hash & min_t(u32, HASHTAB_MAP_LOCK_MASK, htab->n_buckets - 1); preempt_disable(); + raw_local_irq_save(flags); if (unlikely(__this_cpu_inc_return(*(htab->map_locked[hash])) != 1)) { __this_cpu_dec(*(htab->map_locked[hash])); + raw_local_irq_restore(flags); preempt_enable(); return -EBUSY; } - raw_spin_lock_irqsave(&b->raw_lock, flags); + raw_spin_lock(&b->raw_lock); *pflags = flags; return 0; @@ -172,8 +174,9 @@ static inline void htab_unlock_bucket(const struct bpf_htab *htab, unsigned long flags) { hash = hash & min_t(u32, HASHTAB_MAP_LOCK_MASK, htab->n_buckets - 1); - raw_spin_unlock_irqrestore(&b->raw_lock, flags); + raw_spin_unlock(&b->raw_lock); __this_cpu_dec(*(htab->map_locked[hash])); + raw_local_irq_restore(flags); preempt_enable(); }