From nobody Mon Feb 9 06:24:12 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 04728274B5C; Fri, 10 Oct 2025 09:15:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760087704; cv=none; b=hoPHb3pi2Z/wvrkPrw8ZU/35pGvus8Fk74taGsTR45CVPMh+Cp5LwboW3ynTMZ4tiuLqbB6DpFxf0szU31/eWCngRTQJqsq+WQlvAey/9etAlc58IbrnMTC1KbNVcFXerzWfQ3J+TcXzsvNv5dlS5lPWEwcMV1RPtRonYWWbdBs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760087704; c=relaxed/simple; bh=ovGLFVCTGYuUOq4yNzliDM5OKa3CSQx0e3n0oSGzHFo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=SppcJl8F+we0LqxX76b7rJlMvtbspa6QrthD1iblenA0IIEfCXb5yt9/vZMnwi7APTe9fU3uFmxPdUKamKK8abLjwnhNwB39jC89xepncjElSwVamSM8YS6LE59fRcHsZyo6S96hqMQjaIS7OXG1U56Dh7uH63WtZdJqGUp9QbA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=puSKUgh7; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="puSKUgh7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D6D4CC4CEF1; Fri, 10 Oct 2025 09:15:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1760087703; bh=ovGLFVCTGYuUOq4yNzliDM5OKa3CSQx0e3n0oSGzHFo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=puSKUgh74qhPenhdcqpgluAILDfsmC+ftc5uyGPFAd+eYy+xWsCgA9OanqBdpAPcn XnM1VH4MeubcQ5NFdG5pudsTvnmAR0ytwnAyhwqYRigYUuHnrjhHHuwsMhL76wEwqt O4uGN1KEwmSV86kf2pTNUi2dvD6ObfgYxdNUcYeC8Xnc6ILbEDWda3QnRw7CjKPE6Y XaITSTbXkQ5QkNLtwPbJHamE/oYAH824F3HAjhmlg22Ij18UzYNCMtT/W2FxMDOtLT vJWTc+UR6TXC6+Obf0MHiL8HHGZquw/tLHy2mwbTQQdiKxzUHTfu/008IcKR6OcAlC 3LYUwRxXteCdw== From: Yu Kuai To: axboe@kernel.dk, tj@kernel.org, linux-block@vger.kernel.org, cgroups@vger.kernel.org, nilay@linux.ibm.com, bvanassche@acm.org, ming.lei@redhat.com, hch@lst.de Cc: linux-kernel@vger.kernel.org, Yu Kuai Subject: [PATCH v2 04/19] blk-cgroup: don't nest queue_lock under rcu in blkg_lookup_create() Date: Fri, 10 Oct 2025 17:14:29 +0800 Message-ID: <20251010091446.3048529-5-yukuai@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251010091446.3048529-1-yukuai@kernel.org> References: <20251010091446.3048529-1-yukuai@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Yu Kuai Changes to two step: 1) hold rcu lock and do blkg_lookup() from fast path; 2) hold queue_lock directly from slow path, and don't nest it under rcu lock; Prepare to convert protecting blkcg with blkcg_mutex instead of queue_lock; Signed-off-by: Yu Kuai --- block/blk-cgroup.c | 57 +++++++++++++++++++++++++++++----------------- 1 file changed, 36 insertions(+), 21 deletions(-) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index fb40262971c9..3363d2476fed 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -467,22 +467,17 @@ static struct blkcg_gq *blkg_lookup_create(struct blk= cg *blkcg, { struct request_queue *q =3D disk->queue; struct blkcg_gq *blkg; - unsigned long flags; - - WARN_ON_ONCE(!rcu_read_lock_held()); =20 - blkg =3D blkg_lookup(blkcg, q); - if (blkg) - return blkg; - - spin_lock_irqsave(&q->queue_lock, flags); + rcu_read_lock(); blkg =3D blkg_lookup(blkcg, q); if (blkg) { if (blkcg !=3D &blkcg_root && blkg !=3D rcu_dereference(blkcg->blkg_hint)) rcu_assign_pointer(blkcg->blkg_hint, blkg); - goto found; + rcu_read_unlock(); + return blkg; } + rcu_read_unlock(); =20 /* * Create blkgs walking down from blkcg_root to @blkcg, so that all @@ -514,8 +509,6 @@ static struct blkcg_gq *blkg_lookup_create(struct blkcg= *blkcg, break; } =20 -found: - spin_unlock_irqrestore(&q->queue_lock, flags); return blkg; } =20 @@ -2078,6 +2071,18 @@ void blkcg_add_delay(struct blkcg_gq *blkg, u64 now,= u64 delta) atomic64_add(delta, &blkg->delay_nsec); } =20 +static inline struct blkcg_gq *blkg_lookup_tryget(struct blkcg_gq *blkg) +{ +retry: + if (blkg_tryget(blkg)) + return blkg; + + blkg =3D blkg->parent; + if (blkg) + goto retry; + + return NULL; +} /** * blkg_tryget_closest - try and get a blkg ref on the closet blkg * @bio: target bio @@ -2090,20 +2095,30 @@ void blkcg_add_delay(struct blkcg_gq *blkg, u64 now= , u64 delta) static inline struct blkcg_gq *blkg_tryget_closest(struct bio *bio, struct cgroup_subsys_state *css) { - struct blkcg_gq *blkg, *ret_blkg =3D NULL; + struct request_queue *q =3D bio->bi_bdev->bd_queue; + struct blkcg *blkcg =3D css_to_blkcg(css); + struct blkcg_gq *blkg; =20 rcu_read_lock(); - blkg =3D blkg_lookup_create(css_to_blkcg(css), bio->bi_bdev->bd_disk); - while (blkg) { - if (blkg_tryget(blkg)) { - ret_blkg =3D blkg; - break; - } - blkg =3D blkg->parent; - } + blkg =3D blkg_lookup(blkcg, q); + if (likely(blkg)) + blkg =3D blkg_lookup_tryget(blkg); rcu_read_unlock(); =20 - return ret_blkg; + if (blkg) + return blkg; + + /* + * Fast path failed, we're probably issuing IO in this cgroup the first + * time, hold lock to create new blkg. + */ + spin_lock_irq(&q->queue_lock); + blkg =3D blkg_lookup_create(blkcg, bio->bi_bdev->bd_disk); + if (blkg) + blkg =3D blkg_lookup_tryget(blkg); + spin_unlock_irq(&q->queue_lock); + + return blkg; } =20 /** --=20 2.51.0