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Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.1.2 Subject: Re: [ext4 io hang] buffered write io hang in balance_dirty_pages Content-Language: en-US To: Ming Lei CC: Matthew Wilcox , Theodore Ts'o , , Andreas Dilger , , Andrew Morton , , , Dave Chinner , Eric Sandeen , Christoph Hellwig , Zhang Yi , yangerkun , Baokun Li References: From: Baokun Li In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.174] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggpeml500021.china.huawei.com (7.185.36.21) X-CFilter-Loop: Reflected X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: D718340024 X-Stat-Signature: t9hppqpwn7fq6ikbcfmjorc5jhqtmdj5 X-HE-Tag: 1682596671-593342 X-HE-Meta: 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 +xRb+dCi WqoWReBR1XBopH0qGHj6M0gHomjQCGWR50/EZSIdyGJLLc33JJnEpRCnEyQOiO/o+qtXC8Noev00O3MnvKjV828MuTVPCBiroROLfX3Ilmieu4OFCgWh0d9NmXpiFkH9/5hjOZqUx4mr6Gu9/8jF6xKEk7vRcuyAnpz/2teyEtk9sJYKd93jKoXx3cw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2023/4/27 18:01, Ming Lei wrote: > On Thu, Apr 27, 2023 at 02:36:51PM +0800, Baokun Li wrote: >> On 2023/4/27 12:50, Ming Lei wrote: >>> Hello Matthew, >>> >>> On Thu, Apr 27, 2023 at 04:58:36AM +0100, Matthew Wilcox wrote: >>>> On Thu, Apr 27, 2023 at 10:20:28AM +0800, Ming Lei wrote: >>>>> Hello Guys, >>>>> >>>>> I got one report in which buffered write IO hangs in balance_dirty_pages, >>>>> after one nvme block device is unplugged physically, then umount can't >>>>> succeed. >>>> That's a feature, not a bug ... the dd should continue indefinitely? >>> Can you explain what the feature is? And not see such 'issue' or 'feature' >>> on xfs. >>> >>> The device has been gone, so IMO it is reasonable to see FS buffered write IO >>> failed. Actually dmesg has shown that 'EXT4-fs (nvme0n1): Remounting >>> filesystem read-only'. Seems these things may confuse user. >> >> The reason for this difference is that ext4 and xfs handle errors >> differently. >> >> ext4 remounts the filesystem as read-only or even just continues, vfs_write >> does not check for these. > vfs_write may not find anything wrong, but ext4 remount could see that > disk is gone, which might happen during or after remount, however. > >> xfs shuts down the filesystem, so it returns a failure at >> xfs_file_write_iter when it finds an error. >> >> >> ``` ext4 >> ksys_write >>  vfs_write >>   ext4_file_write_iter >>    ext4_buffered_write_iter >>     ext4_write_checks >>      file_modified >>       file_modified_flags >>        __file_update_time >>         inode_update_time >>          generic_update_time >>           __mark_inode_dirty >>            ext4_dirty_inode ---> 2. void func, No propagating errors out >>             __ext4_journal_start_sb >>              ext4_journal_check_start ---> 1. Error found, remount-ro >>     generic_perform_write ---> 3. No error sensed, continue >>      balance_dirty_pages_ratelimited >>       balance_dirty_pages_ratelimited_flags >>        balance_dirty_pages >>         // 4. Sleeping waiting for dirty pages to be freed >>         __set_current_state(TASK_KILLABLE) >>         io_schedule_timeout(pause); >> ``` >> >> ``` xfs >> ksys_write >>  vfs_write >>   xfs_file_write_iter >>    if (xfs_is_shutdown(ip->i_mount)) >>      return -EIO;    ---> dd fail >> ``` > Thanks for the info which is really helpful for me to understand the > problem. > >>>> balance_dirty_pages() is sleeping in KILLABLE state, so kill -9 of >>>> the dd process should succeed. >>> Yeah, dd can be killed, however it may be any application(s), :-) >>> >>> Fortunately it won't cause trouble during reboot/power off, given >>> userspace will be killed at that time. >>> >>> >>> >>> Thanks, >>> Ming >>> >> Don't worry about that, we always set the current thread to TASK_KILLABLE >> >> while waiting in balance_dirty_pages(). > I have another concern, if 'dd' isn't killed, dirty pages won't be cleaned, and > these (big amount)memory becomes not usable, and typical scenario could be USB HDD > unplugged. > > > thanks, > Ming Yes, it is unreasonable to continue writing data with the previously opened fd after the file system becomes read-only, resulting in dirty page accumulation. I provided a patch in another reply. Could you help test if it can solve your problem? If it can indeed solve your problem, I will officially send it to the email list. -- With Best Regards, Baokun Li .