From patchwork Sun Aug 21 03:32:21 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Hou Tao X-Patchwork-Id: 12949855 X-Patchwork-Delegate: bpf@iogearbox.net Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 79D8AC32792 for ; Sun, 21 Aug 2022 03:14:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229806AbiHUDO3 (ORCPT ); Sat, 20 Aug 2022 23:14:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50532 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231214AbiHUDOV (ORCPT ); Sat, 20 Aug 2022 23:14:21 -0400 Received: from dggsgout12.his.huawei.com (unknown [45.249.212.56]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6EE16101EE for ; Sat, 20 Aug 2022 20:14:19 -0700 (PDT) Received: from mail02.huawei.com (unknown [172.30.67.143]) by dggsgout12.his.huawei.com (SkyGuard) with ESMTP id 4M9LCL1dd7z6T4x8 for ; Sun, 21 Aug 2022 11:12:46 +0800 (CST) Received: from huaweicloud.com (unknown [10.175.124.27]) by APP2 (Coremail) with SMTP id Syh0CgAH8r0DowFjsgGLAg--.45130S5; Sun, 21 Aug 2022 11:14:17 +0800 (CST) From: Hou Tao To: bpf@vger.kernel.org, Song Liu Cc: Hao Sun , Sebastian Andrzej Siewior , Andrii Nakryiko , Yonghong Song , Alexei Starovoitov , Daniel Borkmann , Martin KaFai Lau , KP Singh , "David S . Miller" , Jakub Kicinski , Stanislav Fomichev , Hao Luo , Jiri Olsa , John Fastabend , Lorenz Bauer , houtao1@huawei.com Subject: [PATCH 1/3] bpf: Disable preemption when increasing per-cpu map_locked Date: Sun, 21 Aug 2022 11:32:21 +0800 Message-Id: <20220821033223.2598791-2-houtao@huaweicloud.com> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20220821033223.2598791-1-houtao@huaweicloud.com> References: <20220821033223.2598791-1-houtao@huaweicloud.com> MIME-Version: 1.0 X-CM-TRANSID: Syh0CgAH8r0DowFjsgGLAg--.45130S5 X-Coremail-Antispam: 1UD129KBjvJXoWxWFykXw17Aw1UWw1fKF4xXrb_yoW5Aw13pF 48GF9Yyw48XF9a9a9Fqr1Iqr15Jw1xK3yIy3ykGFW8Zr45Ar1fXr1xtFySqF1Fvr9xArsa vr42qa1Yyr4UAFDanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUB0b4IE77IF4wAFF20E14v26rWj6s0DM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6r1S6rWUM7CIcVAFz4kK6r1j6r18M28IrcIa0xkI8VA2jI8067AKxVWUGw A2048vs2IY020Ec7CjxVAFwI0_Gr0_Xr1l8cAvFVAK0II2c7xJM28CjxkF64kEwVA0rcxS w2x7M28EF7xvwVC0I7IYx2IY67AKxVWDJVCq3wA2z4x0Y4vE2Ix0cI8IcVCY1x0267AKxV W8Jr0_Cr1UM28EF7xvwVC2z280aVAFwI0_GcCE3s1l84ACjcxK6I8E87Iv6xkF7I0E14v2 6rxl6s0DM2AIxVAIcxkEcVAq07x20xvEncxIr21l5I8CrVACY4xI64kE6c02F40Ex7xfMc Ij6xIIjxv20xvE14v26r1j6r18McIj6I8E87Iv67AKxVWUJVW8JwAm72CE4IkC6x0Yz7v_ Jr0_Gr1lF7xvr2IYc2Ij64vIr41lFIxGxcIEc7CjxVA2Y2ka0xkIwI1l42xK82IYc2Ij64 vIr41l4I8I3I0E4IkC6x0Yz7v_Jr0_Gr1lx2IqxVAqx4xG67AKxVWUJVWUGwC20s026x8G jcxK67AKxVWUGVWUWwC2zVAF1VAY17CE14v26r4a6rW5MIIYrxkI7VAKI48JMIIF0xvE2I x0cI8IcVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2IY6xkF7I0E14v26r4j6F4UMIIF0xvE42xK 8VAvwI8IcIk0rVWUJVWUCwCI42IY6I8E87Iv67AKxVWUJVW8JwCI42IY6I8E87Iv6xkF7I 0E14v26r4j6r4UJbIYCTnIWIevJa73UjIFyTuYvjxU2mL9UUUUU X-CM-SenderInfo: xkrx3t3r6k3tpzhluzxrxghudrp/ X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net From: Hou Tao Per-cpu htab->map_locked is used to prohibit the concurrent accesses from both NMI and non-NMI contexts. But since 74d862b682f51 ("sched: Make migrate_disable/enable() independent of RT"), migrations_disable() is also preemptible under !PREEMPT_RT case, so now map_locked also disallows concurrent updates from normal contexts (e.g. userspace processes) unexpectedly as shown below: process A process B htab_map_update_elem() htab_lock_bucket() migrate_disable() /* return 1 */ __this_cpu_inc_return() /* preempted by B */ htab_map_update_elem() /* the same bucket as A */ htab_lock_bucket() migrate_disable() /* return 2, so lock fails */ __this_cpu_inc_return() return -EBUSY A fix that seems feasible is using in_nmi() in htab_lock_bucket() and only checking the value of map_locked for nmi context. But it will re-introduce dead-lock on bucket lock if htab_lock_bucket() is re-entered through non-tracing program (e.g. fentry program). So fixing it by using disable_preempt() instead of migrate_disable() when increasing htab->map_locked. However when htab_use_raw_lock() is false, bucket lock will be a sleepable spin-lock and it breaks disable_preempt(), so still use migrate_disable() for spin-lock case. Signed-off-by: Hou Tao Reviewed-by: Hao Luo --- kernel/bpf/hashtab.c | 23 ++++++++++++++++++----- 1 file changed, 18 insertions(+), 5 deletions(-) diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c index 6c530a5e560a..ad09da139589 100644 --- a/kernel/bpf/hashtab.c +++ b/kernel/bpf/hashtab.c @@ -162,17 +162,25 @@ static inline int htab_lock_bucket(const struct bpf_htab *htab, unsigned long *pflags) { unsigned long flags; + bool use_raw_lock; hash = hash & HASHTAB_MAP_LOCK_MASK; - migrate_disable(); + use_raw_lock = htab_use_raw_lock(htab); + if (use_raw_lock) + preempt_disable(); + else + migrate_disable(); if (unlikely(__this_cpu_inc_return(*(htab->map_locked[hash])) != 1)) { __this_cpu_dec(*(htab->map_locked[hash])); - migrate_enable(); + if (use_raw_lock) + preempt_enable(); + else + migrate_enable(); return -EBUSY; } - if (htab_use_raw_lock(htab)) + if (use_raw_lock) raw_spin_lock_irqsave(&b->raw_lock, flags); else spin_lock_irqsave(&b->lock, flags); @@ -185,13 +193,18 @@ static inline void htab_unlock_bucket(const struct bpf_htab *htab, struct bucket *b, u32 hash, unsigned long flags) { + bool use_raw_lock = htab_use_raw_lock(htab); + hash = hash & HASHTAB_MAP_LOCK_MASK; - if (htab_use_raw_lock(htab)) + if (use_raw_lock) raw_spin_unlock_irqrestore(&b->raw_lock, flags); else spin_unlock_irqrestore(&b->lock, flags); __this_cpu_dec(*(htab->map_locked[hash])); - migrate_enable(); + if (use_raw_lock) + preempt_enable(); + else + migrate_enable(); } static bool htab_lru_map_delete_node(void *arg, struct bpf_lru_node *node);