From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=95.215.58.190 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793268697; b=FIR5/a6PEUlnsxdWqs465a1jiE7GnUGwDRekPJ3NtJJlp+ct40LhPxM8Lfs1rGoDhfL5 5A8RMg39eTsrzXzYf0dS0rcoluMjLh8MUceB4VnQqzUqXbOtmB8yWeKYfLCYhePqheLhH FGBPkt4K9zqFB03u+p2LjWbCkVEspF6xl9mb/QH2k+kg+OOXocLgv5YlaDUn5BXFdibs/ YTDhvJLC4TUR01QuYuVXwMwBprUi5uH+v0uqMgRw5XLnQV0eqDWADY2eWe0ej2SdFOMJR QrDcHZGNGBqm1eTDgbr2iFnw4ChdQ3RAs51WEz+Rlv4br2kPHjPKHd3mJ53VzUmCNxQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793268697; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:Message-ID:Date:MIME-Version:User-Agent: Cc:Subject:To:References:From:In-Reply-To:Content-Type: Content-Transfer-Encoding; bh=FAoeFjOhHMIomvSZEyPcUceFOZEousEjiVEkUk7cB2Y=; b=BmEDXBI6++dyuWlYO5qOuQBiUpfjRL+y1SiXyq3nTCpnKwSCJQz62+ui2/0k7TS66ieZ iKnKkJ12Rf3CW/4BP/2scJRyrs6CR+xchr+pg0yoLbGv3JPnYui8IzSi3OftrlZAznALD /eMxfccj7DQOl9YV1W4Ono5cvCGNQTZSEc7v3AhWAInV+nY69Uj66Rf/dBw8UMJxSDFc1 YSzGGiutbTNTCScWoSdXn9QCphLaafXFKXrl0/AKsNulAwqMPiIs2D/w4bVVDgQJxlc5u El0IT1qql7G4iG0+g7Z/gdzZ+ckQ+kKRnQ3IzIaJs1LYAKxEJdhvS8trubdDgpQbA4A== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=W5WC4w0c; arc=none smtp.remote-ip=95.215.58.190 Received: from mta1.migadu.com (out-190.mta1.migadu.com [95.215.58.190]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 25C60606A326 for ; Thu, 29 Oct 2026 10:11:36 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 25C60606A326 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=W5WC4w0c X-Envelope-To: bpf@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=O6pECeJaIkk7IfSov1GVY8i4R6cQbSZNmIkkj1P7D6Q=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793268695; v=1; x=1793873495; b=W5WC4w0csS4VEBLZ2tQ0uytPiTEYb99WY1GvVsXg6l0O8ex/VRZXKkrvDBct7VCmR2++I9yt J1Tzsp1mH2e0cfsCaugOhV+bVlES9qtmuDXLzyvlpvaYXbNsekpoZ3NVes9FyZF9eS3QIzsbDxr 13N8iOXXWc173Mkp2JmAx2cA= X-Envelope-To: bpf@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 73988b42a70c48c5; Thu, 29 Oct 2026 10:11:34 +0000 X-Mizu-Trace-ID: 73988b42a70c48c5 X-Migadu-Flow: FLOW_OUT Message-ID: <895cb52c-1542-4ff7-abaf-844a73126fa8@linux.dev> Date: Thu, 29 Oct 2026 18:11:25 +0800 X-Mailing-List: bpf@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Cc: cui.tao@linux.dev, josef@toxicopanda.com, axboe@kernel.dk, cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, andrii@kernel.org, eddyz87@gmail.com, ast@kernel.org, daniel@iogearbox.net, linux-kselftest@vger.kernel.org, cuitao@kylinos.cn, ameryhung@gmail.com, alexei.starovoitov@gmail.com Subject: Re: [PATCH 2/5] blk-iocost: add BPF struct_ops cost model support To: Tejun Heo References: <20261028143534.135968-1-cui.tao@linux.dev> <20261028143534.135968-3-cui.tao@linux.dev> <0753eaa990c954aa56a0c5fa8ba302e2@kernel.org> From: Tao Cui In-Reply-To: <0753eaa990c954aa56a0c5fa8ba302e2@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hello Tejun, 在 2026/10/29 04:09, Tejun Heo 写道: > Hello, Tao. > > On Wed, Oct 28, 2026 at 10:35:31PM +0800, Tao Cui wrote: >> +/* >> +/* >> + * Deliver iocg_init()/iocg_free() to the cgroups already online on the > > The comment opens with "/*" twice. clang warns "'/*' within block comment > [-Wcomment]" and CONFIG_WERROR builds break. > A stray line was left over from an earlier edit. Sorry about that. >> + /* >> + * A blkg which never went online never reached the >> + * radix tree, so it must not receive an init either; >> ... >> + if (!iocg || !iocg->pd.online) >> + continue; > > blkg_create() adds a blkg to q->blkg_list only after radix_tree_insert() > succeeds, so the blkgs skipped here are the ones blkg_destroy() already > took offline, not ones that never reached the radix tree. > You're right, the comment described the wrong blkgs. It goes away with the walk, which I'll drop in v12 together with the callbacks. >> + if (!disk_live(disk)) { >> + mutex_unlock(&q->rq_qos_mutex); >> + blk_mq_unfreeze_queue(q, memflags); >> + blkdev_put_no_open(bdev); >> + return -ENODEV; >> + } > > The guard() suggestion from v10 was only partly applied. This unlock, > unfreeze and put sequence is repeated on three error paths. > I'll fold the reg error path into a single out label. Detach no longer needs the freeze after the v12 rework. >> + /* >> + * Scope the mutex so the tail bdev put runs with blkcg_mutex >> + * already released: dropping the last device reference can >> + * reach disk_release() -> blkcg_exit_disk() -> >> + * blkg_destroy_all(), which takes q->blkcg_mutex. >> + */ >> + { >> + guard(mutex)(&q->blkcg_mutex); > > The bare { } block isn't necessary, and ioc_bpf_detach() has the same > block with the same comment. Can you drop them? > I'll drop both. >> + /* >> + * The attachment is checked under rq_qos_mutex first, so an unmatched >> + * detach exits without freezing. >> + */ >> + mutex_lock(&q->rq_qos_mutex); >> + spin_lock_irq(&q->queue_lock); >> + ioc = q_to_ioc(q); >> + if (ioc) { >> + spin_lock(&ioc->lock); >> + matched = ioc_attached_model_locked(ioc) == ops && >> + ioc->bpf_link == link; >> ... > > The same 11 lines check the attachment again after the freeze. The check > under rq_qos_mutex after the freeze is the one that matters. > This goes away with the freeze removal: detach becomes a single mutex-critical section. >> +/* >> + * Pluggable cost model interface for blk-iocost. >> + * >> + * A BPF struct_ops implementation can take over the cost model of one device. >> ... >> + * offline and its free. Both callbacks are called with ioc->lock held and must >> + * not sleep; the delivery points nest inside queue_lock except for iocg_free() >> + * from ioc_pd_free() in blkg_free_workfn(). >> + */ > > This restates the attach mechanics and lists the call sites. The comments > and descriptions in general are still long and narrate mechanics. > v12 folds everything back into blk-iocost.c, so the private header and the long interface comment both go away. Thanks, Tao > Thanks. > > -- > tejun