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([2a00:79e0:2e7c:8:b83:4858:813e:dbe7]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-304ed5d26d1sm10147252eec.30.2026.06.01.14.50.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 01 Jun 2026 14:50:10 -0700 (PDT) Message-ID: <8709b8e7-8328-47e8-950f-e5726bd70dbc@gmail.com> Date: Mon, 1 Jun 2026 14:50:08 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] blk-iocost: use irq-safe locking in cgroup handlers To: Yu Kuai , tj@kernel.org, josef@toxicpanda.com Cc: axboe@kernel.dk, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260601061312.896801-1-yukuai@fygo.io> Content-Language: en-US From: Bart Van Assche In-Reply-To: <20260601061312.896801-1-yukuai@fygo.io> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 5/31/26 11:13 PM, Yu Kuai wrote: > @@ -3378,14 +3378,14 @@ static u64 ioc_cost_model_prfill(struct seq_file *sf, > if (!dname) > return 0; > > - spin_lock(&ioc->lock); > + spin_lock_irq(&ioc->lock); > seq_printf(sf, "%s ctrl=%s model=linear " > "rbps=%llu rseqiops=%llu rrandiops=%llu " > "wbps=%llu wseqiops=%llu wrandiops=%llu\n", > dname, ioc->user_cost_model ? "user" : "auto", > u[I_LCOEF_RBPS], u[I_LCOEF_RSEQIOPS], u[I_LCOEF_RRANDIOPS], > u[I_LCOEF_WBPS], u[I_LCOEF_WSEQIOPS], u[I_LCOEF_WRANDIOPS]); > - spin_unlock(&ioc->lock); > + spin_unlock_irq(&ioc->lock); > return 0; > } This change is wrong. ioc_cost_model_prfill() only has one caller, namely blkcg_print_blkgs(). blkcg_print_blkgs() calls the above function with interrupts disabled. The spin_unlock_irq(&ioc->lock) at the end of the above function enables interrupts while q->queue_lock is held. If an interrupt happens on the same CPU core before q->queue_lock is unlocked, and that interrupt tries to lock q->queue_lock, a deadlock will occur. Bart.