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[2603:800c:1a02:1bae:a7fa:157f:969a:4cde]) by smtp.gmail.com with ESMTPSA id z14-20020a1709027e8e00b00176a2d23d1asm1914493pla.56.2022.11.30.12.20.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Nov 2022 12:20:16 -0800 (PST) Sender: Tejun Heo Date: Wed, 30 Nov 2022 10:20:15 -1000 From: Tejun Heo To: Li Nan Cc: josef@toxicpanda.com, axboe@kernel.dk, cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, yukuai3@huawei.com, yi.zhang@huawei.com Subject: Re: [PATCH -next v2 5/9] blk-iocost: fix divide by 0 error in calc_lcoefs() Message-ID: References: <20221130132156.2836184-1-linan122@huawei.com> <20221130132156.2836184-6-linan122@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221130132156.2836184-6-linan122@huawei.com> Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Wed, Nov 30, 2022 at 09:21:52PM +0800, Li Nan wrote: > echo max of u64 to cost.model can cause divide by 0 error. > > # echo 8:0 rbps=18446744073709551615 > /sys/fs/cgroup/io.cost.model > > divide error: 0000 [#1] PREEMPT SMP > RIP: 0010:calc_lcoefs+0x4c/0xc0 > Call Trace: > > ioc_refresh_params+0x2b3/0x4f0 > ioc_cost_model_write+0x3cb/0x4c0 > ? _copy_from_iter+0x6d/0x6c0 > ? kernfs_fop_write_iter+0xfc/0x270 > cgroup_file_write+0xa0/0x200 > kernfs_fop_write_iter+0x17d/0x270 > vfs_write+0x414/0x620 > ksys_write+0x73/0x160 > __x64_sys_write+0x1e/0x30 > do_syscall_64+0x35/0x80 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > calc_lcoefs() uses the input value of cost.model in DIV_ROUND_UP_ULL, > overflow would happen if bps plus IOC_PAGE_SIZE is greater than > ULLONG_MAX, it can cause divide by 0 error.I_LCOEF_MAX is introduced to > prevent it. > > Signed-off-by: Li Nan > --- > block/blk-iocost.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/block/blk-iocost.c b/block/blk-iocost.c > index 3a96cd557c47..f4a754b9d10f 100644 > --- a/block/blk-iocost.c > +++ b/block/blk-iocost.c > @@ -306,6 +306,9 @@ enum { > IOC_PAGE_SIZE = 1 << IOC_PAGE_SHIFT, > IOC_SECT_TO_PAGE_SHIFT = IOC_PAGE_SHIFT - SECTOR_SHIFT, > > + /* avoid overflow */ > + I_LCOEF_MAX = ULLONG_MAX - IOC_PAGE_SIZE, > + > /* if apart further than 16M, consider randio for linear model */ > LCOEF_RANDIO_PAGES = 4096, > }; > @@ -3431,6 +3434,8 @@ static ssize_t ioc_cost_model_write(struct kernfs_open_file *of, char *input, > goto out_unlock; > } > > + if (v > I_LCOEF_MAX) > + goto out_unlock; This is kinda round-about. Can you just make calc_lcoefs to not divide by zero (e.g. just make it 1 if zero)? Thanks. -- tejun