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NALASPPMTA02.qualcomm.com (8.17.1.5/8.17.1.5) with ESMTPS id 40MGT52M014482 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 22 Jan 2024 16:29:05 GMT Received: from [10.216.2.182] (10.80.80.8) by nalasex01a.na.qualcomm.com (10.47.209.196) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.40; Mon, 22 Jan 2024 08:29:02 -0800 Message-ID: Date: Mon, 22 Jan 2024 21:58:58 +0530 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH] fs: improve dump_mapping() robustness Content-Language: en-US To: Baolin Wang , Al Viro CC: , , , , , , References: <937ab1f87328516821d39be672b6bc18861d9d3e.1705391420.git.baolin.wang@linux.alibaba.com> <20240118013857.GO1674809@ZenIV> <8f52414c-e0f2-4931-9b32-5c22f1d581f0@linux.alibaba.com> From: Charan Teja Kalla In-Reply-To: <8f52414c-e0f2-4931-9b32-5c22f1d581f0@linux.alibaba.com> Content-Type: 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 s1qIxWgN kMu0Y/VnzbbdpMD2WjfSRsMaGUV+seLmLkBbAMcYOqmcpgmoZPjSLMjWMA7PKfno/Tx0BAP9QxEx/SDUcklhW6sj4nNHMTKaBHgWzIH+kVf3OPQjoOg+410p/RL1lRq2O1MiO+xdemg7mBurDj95jpxUln12sJXL34nNChSPQXs0DSvEumzLrcztP6GhLGyT32bP4At7KYDaqjqaq1M/XR26wZSdLHuvbTvXq+Ypk5BMqBwI0JGHWj0RTsO48n7kTIh7V7+JNlAJl+Ic+TxD9WVPr4lBYI4aUyiE+ 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: List-Subscribe: List-Unsubscribe: On 1/22/2024 12:47 PM, Baolin Wang wrote: >> >> We too seen the below crash while printing the dentry name. >> >> aops:shmem_aops ino:5e029 dentry name:"dev/zero" >> flags: >> 0x8000000000080006(referenced|uptodate|swapbacked|zone=2|kasantag=0x0) >> raw: 8000000000080006 ffffffc033b1bb60 ffffffc033b1bb60 ffffff8862537600 >> raw: 0000000000000001 0000000000000000 00000003ffffffff ffffff807fe64000 >> page dumped because: migration failure >> migrating pfn aef223 failed ret:1 >> page:000000009e72a120 refcount:3 mapcount:0 mapping:000000003325dda1 >> index:0x1 pfn:0xaef223 >> memcg:ffffff807fe64000 >> Unable to handle kernel NULL pointer dereference at virtual address >> 0000000000000000 >> Mem abort info: >>    ESR = 0x0000000096000005 >>    EC = 0x25: DABT (current EL), IL = 32 bits >>    SET = 0, FnV = 0 >>    EA = 0, S1PTW = 0 >>    FSC = 0x05: level 1 translation fault >> Data abort info: >>    ISV = 0, ISS = 0x00000005 >>    CM = 0, WnR = 0 >> user pgtable: 4k pages, 39-bit VAs, pgdp=000000090c12d000 >> [0000000000000000] pgd=0000000000000000, p4d=0000000000000000, >> pud=0000000000000000 >> Internal error: Oops: 0000000096000005 [#1] PREEMPT SMP >> >> dentry_name+0x1f8/0x3a8 >> pointer+0x3b0/0x6b8 >> vsnprintf+0x4a4/0x65c >> vprintk_store+0x168/0x4a8 >> vprintk_emit+0x98/0x218 >> vprintk_default+0x44/0x70 >> vprintk+0xf0/0x138 >> _printk+0x54/0x80 >> dump_mapping+0x17c/0x188 >> dump_page+0x1d0/0x2e8 >> offline_pages+0x67c/0x898 >> >> >> >> Not much comfortable with block layer internals, TMK, the below is what >> happening in the my case: >> memoffline                 dput() >> (offline_pages)         (as part of closing of the shmem file) >> ------------         -------------------------------------- >>                     ....... >>             1) dentry_unlink_inode() >>                   hlist_del_init(&dentry->d_u.d_alias); >> >>             2) iput(): >>                 a) inode->i_state |= I_FREEING >>                 ..... >>                 b) evict_inode()->..->shmem_undo_range >>                    1) get the folios with elevated refcount >> 3) do_migrate_range(): >>     a) Because of the elevated >>     refcount in 2.b.1, the >>     migration of this page will >>     be failed. >> >>                    2) truncate_inode_folio() -> >>                      filemap_remove_folio(): >>                   (deletes from the page cache, >>                  set page->mapping=NULL, >>                  decrement the refcount on folio) >>    b) Call dump_page(): >>       1) mapping = page_mapping(page); >>       2) dump_mapping(mapping) >>       a) We unlinked the dentry in 1) >>             thus dentry_ptr from host->i_dentry.first >>             is not a proper one. >> >>           b) dentry name print with %pd is resulting into >>        the mentioned crash. >> >> >> At least in this case, I think __this patchset in its current form can >> help us__. > > This looks another case of NULL pointer access. Thanks for the detailed > analysis. Could you provide a Tested-by or Reviewed-by tag if it can > solve your problem? Seen this issue couple of times, over 3 months back. Not sure if we ever encounter this issue again. Still, will pick this and let you know the side effects of this patch, after thorough testing. Thanks.