From mboxrd@z Thu Jan 1 00:00:00 1970 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 A73EBC2BB3F for ; Wed, 15 Nov 2023 19:39:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234766AbjKOTjw (ORCPT ); Wed, 15 Nov 2023 14:39:52 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58464 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234770AbjKOTjv (ORCPT ); Wed, 15 Nov 2023 14:39:51 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 77131CE for ; Wed, 15 Nov 2023 11:39:43 -0800 (PST) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D5DC7C433CC; Wed, 15 Nov 2023 19:39:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1700077183; bh=dkxPNGPCNErXWoiH6DESwT9n/vM5dMTGP3ic/f13KIw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=cZhGoubinI9eR7dKtgg4gkUd/9msLLEE6E0JKGoOCFeErOwHIcjP9j1Lv8QdxIkq0 17BDOGUatDa/lLBvAkFYB8Z+iNuu/Sij00r8vxFubjQUhZidgwlqm3alEr6oA13LJm mYQEqAbX0m0aq8cEyLnK/eLtP+LuNtrg40YsfPiE= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Tejun Heo , Song Liu , Andrii Nakryiko , Daniel Borkmann , Sasha Levin Subject: [PATCH 6.6 151/603] bpf: Fix unnecessary -EBUSY from htab_lock_bucket Date: Wed, 15 Nov 2023 14:11:36 -0500 Message-ID: <20231115191623.634125282@linuxfoundation.org> X-Mailer: git-send-email 2.42.1 In-Reply-To: <20231115191613.097702445@linuxfoundation.org> References: <20231115191613.097702445@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Song Liu [ Upstream commit d35381aa73f7e1e8b25f3ed5283287a64d9ddff5 ] 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(). Fixes: 20b6cc34ea74 ("bpf: Avoid hashtab deadlock with map_locked") Suggested-by: Tejun Heo Signed-off-by: Song Liu Signed-off-by: Andrii Nakryiko Signed-off-by: Daniel Borkmann Link: https://lore.kernel.org/bpf/7a9576222aa40b1c84ad3a9ba3e64011d1a04d41.camel@linux.ibm.com Link: https://lore.kernel.org/bpf/20231012055741.3375999-1-song@kernel.org Signed-off-by: Sasha Levin --- 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 a8c7e1c5abfac..fd8d4b0addfca 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(); + local_irq_save(flags); if (unlikely(__this_cpu_inc_return(*(htab->map_locked[hash])) != 1)) { __this_cpu_dec(*(htab->map_locked[hash])); + 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])); + local_irq_restore(flags); preempt_enable(); } -- 2.42.0