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Fri, 9 Apr 2021 11:28:10 +0000 (GMT) Received: from b06wcsmtp001.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id E5531A405C; Fri, 9 Apr 2021 11:28:09 +0000 (GMT) Received: from localhost (unknown [9.85.70.102]) by b06wcsmtp001.portsmouth.uk.ibm.com (Postfix) with ESMTP; Fri, 9 Apr 2021 11:28:09 +0000 (GMT) Date: Fri, 9 Apr 2021 16:58:09 +0530 From: riteshh To: Jan Kara Cc: Wen Yang , adilger@dilger.ca, tytso@mit.edu, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, baoyou.xie@alibaba-inc.com Subject: Re: [PATCH] ext4: add a configurable parameter to prevent endless loop in ext4_mb_discard_group_p Message-ID: <20210409112809.n4d6kar62zwzr6af@riteshh-domain> References: <20210409054733.avv3ofqpka4m6xe5@riteshh-domain> <20210409101811.GB20833@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210409101811.GB20833@quack2.suse.cz> X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: w-WGFj3QsyYxPskAxtbyvTE61KTHvx3Q X-Proofpoint-GUID: Iu6q2NcVvLi76SvglBLqgskT11yqGUxo X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.761 definitions=2021-04-09_05:2021-04-09,2021-04-09 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 adultscore=0 suspectscore=0 phishscore=0 lowpriorityscore=0 clxscore=1015 priorityscore=1501 malwarescore=0 mlxlogscore=999 spamscore=0 mlxscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104060000 definitions=main-2104090081 Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On 21/04/09 12:18PM, Jan Kara wrote: > On Fri 09-04-21 11:17:33, riteshh wrote: > > On 21/04/09 02:50AM, Wen Yang wrote: > > > > On Apr 7, 2021, at 5:16 AM, riteshh wrote: > > > >> > > > >> On 21/04/07 03:01PM, Wen Yang wrote: > > > >>> From: Wen Yang > > > >>> > > > >>> The kworker has occupied 100% of the CPU for several days: > > > >>> PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND > > > >>> 68086 root 20 0 0 0 0 R 100.0 0.0 9718:18 kworker/u64:11 > > > >>> > > > >>> And the stack obtained through sysrq is as follows: > > > >>> [20613144.850426] task: ffff8800b5e08000 task.stack: ffffc9001342c000 > > > >>> [20613144.850438] Call Trace: > > > >>> [20613144.850439] []ext4_mb_new_blocks+0x429/0x550 > > > [ext4] > > > >>> [20613144.850439] [] ext4_ext_map_blocks+0xb5e/0xf30 > > > [ext4] > > > >>> [20613144.850441] [] ext4_map_blocks+0x172/0x620 > > > [ext4] > > > >>> [20613144.850442] [] ext4_writepages+0x7e5/0xf00 > > > [ext4] > > > >>> [20613144.850443] [] do_writepages+0x1e/0x30 > > > >>> [20613144.850444] [] > > > __writeback_single_inode+0x45/0x320 > > > >>> [20613144.850444] [] writeback_sb_inodes+0x272/0x600 > > > >>> [20613144.850445] [] __writeback_inodes_wb+0x92/0xc0 > > > >>> [20613144.850445] [] wb_writeback+0x268/0x300 > > > >>> [20613144.850446] [] wb_workfn+0xb4/0x380 > > > >>> [20613144.850447] [] process_one_work+0x189/0x420 > > > >>> [20613144.850447] [] worker_thread+0x4e/0x4b0 > > > >>> > > > >>> The cpu resources of the cloud server are precious, and the server > > > >>> cannot be restarted after running for a long time, so a configuration > > > >>> parameter is added to prevent this endless loop. > > > >> > > > >> Strange, if there is a endless loop here. Then I would definitely see > > > >> if there is any accounting problem in pa->pa_count. Otherwise busy=1 > > > >> should not be set everytime. ext4_mb_show_pa() function may help debug > > > this. > > > >> > > > >> If yes, then that means there always exists either a file preallocation > > > >> or a group preallocation. Maybe it is possible, in some use case. > > > >> Others may know of such use case, if any. > > > > > > > If this code is broken, then it doesn't make sense to me that we would > > > > leave it in the "run forever" state after the patch, and require a sysfs > > > > tunable to be set to have a properly working system? > > > > > > > Is there anything particularly strange about the workload/system that > > > > might cause this? Filesystem is very full, memory is very low, etc? > > > > > > Hi Ritesh and Andreas, > > > > > > Thank you for your reply. Since there is still a faulty machine, we have > > > analyzed it again and found it is indeed a very special case: > > > > > > > > > crash> struct ext4_group_info ffff8813bb5f72d0 > > > struct ext4_group_info { > > > bb_state = 0, > > > bb_free_root = { > > > rb_node = 0x0 > > > }, > > > bb_first_free = 1681, > > > bb_free = 0, > > > > Not related to this issue, but above two variables values doesn't looks > > consistent. > > > > > bb_fragments = 0, > > > bb_largest_free_order = -1, > > > bb_prealloc_list = { > > > next = 0xffff880268291d78, > > > prev = 0xffff880268291d78 ---> *** The list is empty > > > }, > > > > Ok. So when you collected the dump this list was empty. > > No, it is not empty. It has a single element. Note that the structure is at > ffff8813bb5f72d0 so the pointers would have to be like ffff8813bb5f7xxx. Errr, yes right. So the list is not empty. But I guess the other arguments discussed in that mail should still be valid. -ritesh