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GET /api/patches/2227437/?format=api
{ "id": 2227437, "url": "http://patchwork.ozlabs.org/api/patches/2227437/?format=api", "web_url": "http://patchwork.ozlabs.org/project/linux-ext4/patch/20260423173700.GA2187084@chcpu16/", "project": { "id": 8, "url": "http://patchwork.ozlabs.org/api/projects/8/?format=api", "name": "Linux ext4 filesystem development", "link_name": "linux-ext4", "list_id": "linux-ext4.vger.kernel.org", "list_email": "linux-ext4@vger.kernel.org", "web_url": null, "scm_url": null, "webscm_url": null, "list_archive_url": "", "list_archive_url_format": "", "commit_url_format": "" }, "msgid": "<20260423173700.GA2187084@chcpu16>", "list_archive_url": null, "date": "2026-04-23T17:37:16", "name": "[BUG] ext4: KCSAN: lockless i_es_all_nr reads in es_shrinker_info", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "36f03a33f6c68130a49b37bfbb3789c1b16af3c5", "submitter": { "id": 91564, "url": "http://patchwork.ozlabs.org/api/people/91564/?format=api", "name": "Shuhao Fu", "email": "sfual@cse.ust.hk" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/linux-ext4/patch/20260423173700.GA2187084@chcpu16/mbox/", "series": [ { "id": 501229, "url": "http://patchwork.ozlabs.org/api/series/501229/?format=api", "web_url": "http://patchwork.ozlabs.org/project/linux-ext4/list/?series=501229", "date": "2026-04-23T17:37:16", "name": "[BUG] ext4: KCSAN: lockless i_es_all_nr reads in es_shrinker_info", "version": 1, "mbox": "http://patchwork.ozlabs.org/series/501229/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2227437/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2227437/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "\n <SRS0=D6qC=CW=vger.kernel.org=linux-ext4+bounces-16069-patchwork-incoming=ozlabs.org@ozlabs.org>", "X-Original-To": [ "incoming@patchwork.ozlabs.org", "linux-ext4@vger.kernel.org" ], "Delivered-To": [ "patchwork-incoming@legolas.ozlabs.org", "patchwork-incoming@ozlabs.org" ], "Authentication-Results": [ "legolas.ozlabs.org;\n\tdkim=fail reason=\"signature verification failed\" (1024-bit key;\n unprotected) header.d=cse.ust.hk header.i=@cse.ust.hk header.a=rsa-sha256\n header.s=cseusthk header.b=lePdqm4q;\n\tdkim-atps=neutral", "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=ozlabs.org\n (client-ip=2404:9400:2221:ea00::3; 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t=1776965848;\n\th=DKIM-Signature:Date:From:To:Subject:Message-ID:MIME-Version;\n\tbh=ooBVeHO5BNHGyWf9t7ZufVl29d6IT3b4Z7fohAbfVwc=;\n\tb=ZbWEHSL0T/fII8NM4r/zhxiWvhf6D2UYNsBUabgJfepQpQpZPtEJ4B/egsb8mOX9xnFn\n\t 028uS9esS5+iz+9lcXNauKtpde6grj8I9F3VItQpF0gNTgQOFkPOvvWPPRViaQ0zGERPh\n\t eUKbexZBOi+vPQt890sADqcc4J4pE1Y5l8=" ], "ARC-Authentication-Results": [ "i=2; smtp.subspace.kernel.org;\n dmarc=pass (p=none dis=none) header.from=cse.ust.hk;\n spf=pass smtp.mailfrom=cse.ust.hk;\n dkim=fail (1024-bit key) header.d=cse.ust.hk header.i=@cse.ust.hk\n header.b=lePdqm4q reason=\"signature verification failed\";\n arc=fail smtp.client-ip=143.89.41.157", "i=1; cse.ust.hk;\n arc=none smtp.remote-ip=143.89.191.45" ], "DKIM-Signature": "v=1; a=rsa-sha256; c=relaxed/relaxed; d=cse.ust.hk;\n\ts=cseusthk; t=1776965848;\n\tbh=ooBVeHO5BNHGyWf9t7ZufVl29d6IT3b4Z7fohAbfVwc=;\n\th=Date:From:To:Cc:Subject:From;\n\tb=lePdqm4qB7eWJYQqIPHt9brQXb3SuRd91nj6sGelvFEovd3IICbaMLCqYMUwOfDnd\n\t DZh1/AOXe3Uek/B2JI3o56S9yIaY7VcaoTDxinZi8E/Ite3YXlkps61XDv1OkefZtM\n\t p+QyBDqYU0kvXG5tO2FM/0pfJ8wHv8ZzV9mZ3XLk=", "Date": "Fri, 24 Apr 2026 01:37:16 +0800", "From": "Shuhao Fu <sfual@cse.ust.hk>", "To": "\"Theodore Ts'o\" <tytso@mit.edu>, linux-ext4@vger.kernel.org", "Cc": "linux-kernel@vger.kernel.org", "Subject": "[BUG] ext4: KCSAN: lockless i_es_all_nr reads in es_shrinker_info", "Message-ID": "<20260423173700.GA2187084@chcpu16>", "Precedence": "bulk", "X-Mailing-List": "linux-ext4@vger.kernel.org", "List-Id": "<linux-ext4.vger.kernel.org>", "List-Subscribe": "<mailto:linux-ext4+subscribe@vger.kernel.org>", "List-Unsubscribe": "<mailto:linux-ext4+unsubscribe@vger.kernel.org>", "MIME-Version": "1.0", "Content-Type": "text/plain; charset=us-ascii", "Content-Disposition": "inline", "X-Env-From": "sfual", "X-Spam-Status": "No, score=0.0 required=5.0 tests=ARC_SIGNED,ARC_VALID,\n\tDKIM_INVALID,DKIM_SIGNED,DMARC_NONE,HEADER_FROM_DIFFERENT_DOMAINS,\n\tMAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=disabled\n\tversion=4.0.1", "X-Spam-Checker-Version": "SpamAssassin 4.0.1 (2024-03-25) on gandalf.ozlabs.org" }, "content": "Hi,\n\nReading /proc/fs/ext4/<sb>/es_shrinker_info can overlap with extent-status\nupdates and trigger KCSAN reports on the per-inode ES counters (I saw this on\ni_es_all_nr; i_es_shk_nr is read the same way in this proc path). From what I\ncan see, the user-visible impact appears limited to stale/inconsistent procfs\nstats output (I do not have evidence of corruption or crash from this path).\n\nI reproduced this on a local KCSAN-instrumented tree based on linux commit\nd8a9a4b11a13, using an x86_64 QEMU workload with userspace reader/writer loops.\nTo increase the race window, I added small debug-only hooks in my local tree:\nafter the writer updates the counter, it briefly delays and records which inode\nit just touched; the proc reader then samples that inode's counters during the\ns_es_list walk. I also wrapped the i_es_all_nr load in a local helper\next4_es_shrinker_read_all_nr() so the read-side stack has a stable symbol;\nupstream reads happen directly in ext4_seq_es_shrinker_info_show().\n\nWith that setup, KCSAN prints the following summary line (naming the two\nracing functions):\n\n BUG: KCSAN: data-race in ext4_es_init_extent / ext4_es_shrinker_read_all_nr\n\nThe first clean hit in my local log was:\n\n read to 0xffff917cc15222c8 of 4 bytes by task 107 on cpu 0:\n ext4_es_shrinker_read_all_nr+0x26/0x50\n ext4_es_kcsan_probe_hot_inode+0x2b9/0x400\n ext4_seq_es_shrinker_info_show+0x9b/0xd40\n ...\n __x64_sys_sendfile64+0xc2/0x100\n do_syscall_64+0x13f/0x3c0\n\n write (reordered) to 0xffff917cc15222c8 of 4 bytes by task 108 on cpu 2:\n ext4_es_init_extent+0x6aa/0xa00\n __es_insert_extent+0x477/0xaa0\n ...\n ext4_do_fallocate+0x127/0x310\n __x64_sys_fallocate+0x75/0xb0\n\nI then saw the same pair again later in the same run (for example around\n129.529391 and 129.579938), still on the same 4-byte address.\n\nIt looks like i_es_all_nr and i_es_shk_nr are documented as protected by\ni_es_lock, and writers update them under i_es_lock, but\next4_seq_es_shrinker_info_show() reads them while walking the list under\ns_es_lock (the list lock), not i_es_lock.\n\nThe reproducer shape from normal userspace APIs is one reader loop running\ncat /proc/fs/ext4/<sb>/es_shrinker_info while a writer loop runs fallocate,\nbuffered writes, punch-hole, and truncate on the same filesystem.\n\nSince this appears to be an observational procfs stats path, would you prefer\nmarking these loads with data_race(...) so the intentionally approximate reads\nare explicit and this path stops generating repeated KCSAN warnings?\n\nThe rough change I had in mind is:\n\n+++ b/fs/ext4/extents_status.c\n@@\n int ext4_seq_es_shrinker_info_show(struct seq_file *seq, void *v)\n {\n \t...\n \tlist_for_each_entry(ei, &sbi->s_es_list, i_es_list) {\n \t\tinode_cnt++;\n \t\tei_all_nr = data_race(ei->i_es_all_nr);\n \t\tei_shk_nr = data_race(ei->i_es_shk_nr);\n \t\t...\n }\n\nIf this direction is preferred, I can send a formal patch.\n\nThanks,\nShuhao", "diff": "diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c\nindex ... .. ...\n--- a/fs/ext4/extents_status.c\n", "prefixes": [ "BUG" ] }