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GET /api/1.2/patches/2221870/?format=api
{ "id": 2221870, "url": "http://patchwork.ozlabs.org/api/1.2/patches/2221870/?format=api", "web_url": "http://patchwork.ozlabs.org/project/linux-ext4/patch/20260410120318.862164111@kernel.org/", "project": { "id": 8, "url": "http://patchwork.ozlabs.org/api/1.2/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": "<20260410120318.862164111@kernel.org>", "list_archive_url": null, "date": "2026-04-10T12:20:01", "name": "[19/38] kcsan: Replace get_cycles() usage", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "e5fa9bbabd307c9bf414f962883ac06e512535a8", "submitter": { "id": 92397, "url": "http://patchwork.ozlabs.org/api/1.2/people/92397/?format=api", "name": "Thomas Gleixner", "email": "tglx@kernel.org" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/linux-ext4/patch/20260410120318.862164111@kernel.org/mbox/", "series": [ { "id": 499451, "url": "http://patchwork.ozlabs.org/api/1.2/series/499451/?format=api", "web_url": "http://patchwork.ozlabs.org/project/linux-ext4/list/?series=499451", "date": "2026-04-10T12:18:27", "name": "treewide: Cleanup LATCH, CLOCK_TICK_RATE and get_cycles() [ab]use", "version": 1, "mbox": "http://patchwork.ozlabs.org/series/499451/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2221870/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2221870/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "\n <SRS0=Ntkm=CJ=vger.kernel.org=linux-ext4+bounces-15754-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=pass (2048-bit key;\n unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256\n header.s=k20201202 header.b=SQFHopbF;\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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arc=none smtp.client-ip=10.30.226.201" ], "DKIM-Signature": "v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org;\n\ts=k20201202; t=1775823604;\n\tbh=OJyrwmrX6lIri0LIdsFu5GdqSG8VG/nHQeslgTl5R4k=;\n\th=Date:From:To:Cc:Subject:References:From;\n\tb=SQFHopbFA4avzkQltPCDvONKOyWmV73pxkcg27G4tKW1mNfy7PYVk0h6FRJhlowhk\n\t TQQGbFN8xcNa+loyfTw/Ao/LMW9fb2z9STU9hSKk0Q9e4TyhUmpic8YPBLcUkWvS5H\n\t AbfS/R5YsMQyaoKc/WDlm6lhBx4bXYBfs3B4LA3Z/Y/SjzAwbFrEIx6rz/PfITLKPl\n\t d1tT7WhENbDQpyhAelqaE4x97qqSWFBpW6gFyL/Wzy4bWcES9cochVgZgvdNMg3UtL\n\t W9F79+f3Gx3pjpImzUkKb/YiEF7KogJM+PPf5Wjs2H8jaVYTBcG1Ittd3E5H9zOpng\n\t +M493bQX3+83g==", "Date": "Fri, 10 Apr 2026 14:20:01 +0200", "Message-ID": "<20260410120318.862164111@kernel.org>", "User-Agent": "quilt/0.68", "From": "Thomas Gleixner <tglx@kernel.org>", "To": "LKML <linux-kernel@vger.kernel.org>", "Cc": "Marco Elver <elver@google.com>,\n Dmitry Vyukov <dvyukov@google.com>,\n kasan-dev@googlegroups.com,\n Arnd Bergmann <arnd@arndb.de>,\n x86@kernel.org,\n Lu Baolu <baolu.lu@linux.intel.com>,\n iommu@lists.linux.dev,\n Michael Grzeschik <m.grzeschik@pengutronix.de>,\n netdev@vger.kernel.org,\n linux-wireless@vger.kernel.org,\n Herbert Xu <herbert@gondor.apana.org.au>,\n linux-crypto@vger.kernel.org,\n Vlastimil Babka <vbabka@kernel.org>,\n linux-mm@kvack.org,\n David Woodhouse <dwmw2@infradead.org>,\n Bernie Thompson <bernie@plugable.com>,\n linux-fbdev@vger.kernel.org,\n \"Theodore Tso\" <tytso@mit.edu>,\n linux-ext4@vger.kernel.org,\n Andrew Morton <akpm@linux-foundation.org>,\n Uladzislau Rezki <urezki@gmail.com>,\n Andrey Ryabinin <ryabinin.a.a@gmail.com>,\n Thomas Sailer <t.sailer@alumni.ethz.ch>,\n linux-hams@vger.kernel.org,\n \"Jason A. Donenfeld\" <Jason@zx2c4.com>,\n Richard Henderson <richard.henderson@linaro.org>,\n linux-alpha@vger.kernel.org,\n Russell King <linux@armlinux.org.uk>,\n linux-arm-kernel@lists.infradead.org,\n Catalin Marinas <catalin.marinas@arm.com>,\n Huacai Chen <chenhuacai@kernel.org>,\n loongarch@lists.linux.dev,\n Geert Uytterhoeven <geert@linux-m68k.org>,\n linux-m68k@lists.linux-m68k.org,\n Dinh Nguyen <dinguyen@kernel.org>,\n Jonas Bonn <jonas@southpole.se>,\n linux-openrisc@vger.kernel.org,\n Helge Deller <deller@gmx.de>,\n linux-parisc@vger.kernel.org,\n Michael Ellerman <mpe@ellerman.id.au>,\n linuxppc-dev@lists.ozlabs.org,\n Paul Walmsley <pjw@kernel.org>,\n linux-riscv@lists.infradead.org,\n Heiko Carstens <hca@linux.ibm.com>,\n linux-s390@vger.kernel.org,\n \"David S. Miller\" <davem@davemloft.net>,\n sparclinux@vger.kernel.org", "Subject": "[patch 19/38] kcsan: Replace get_cycles() usage", "References": "<20260410120044.031381086@kernel.org>", "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=UTF-8", "X-Spam-Status": "No, score=-1.2 required=5.0 tests=ARC_SIGNED,ARC_VALID,\n\tDKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DMARC_PASS,\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": "KCSAN uses get_cycles() for two purposes:\n\n 1) Seeding the random state with get_cycles() is a historical leftover.\n\n 2) The microbenchmark uses get_cycles(), which provides an unit less\n counter value and is not guaranteed to be functional on all\n systems/platforms.\n\nUse random_get_entropy() for seeding the random state and ktime_get() which\nis universaly functional and provides at least a comprehensible unit.\n\nThis is part of a larger effort to remove get_cycles() usage from\nnon-architecture code.\n\nSigned-off-by: Thomas Gleixner <tglx@kernel.org>\nCc: Marco Elver <elver@google.com>\nCc: Dmitry Vyukov <dvyukov@google.com>\nCc: kasan-dev@googlegroups.com\n---\n kernel/kcsan/core.c | 2 +-\n kernel/kcsan/debugfs.c | 8 ++++----\n 2 files changed, 5 insertions(+), 5 deletions(-)", "diff": "--- a/kernel/kcsan/core.c\n+++ b/kernel/kcsan/core.c\n@@ -798,7 +798,7 @@ void __init kcsan_init(void)\n \tBUG_ON(!in_task());\n \n \tfor_each_possible_cpu(cpu)\n-\t\tper_cpu(kcsan_rand_state, cpu) = (u32)get_cycles();\n+\t\tper_cpu(kcsan_rand_state, cpu) = (u32)random_get_entropy();\n \n \t/*\n \t * We are in the init task, and no other tasks should be running;\n--- a/kernel/kcsan/debugfs.c\n+++ b/kernel/kcsan/debugfs.c\n@@ -58,7 +58,7 @@ static noinline void microbenchmark(unsi\n {\n \tconst struct kcsan_ctx ctx_save = current->kcsan_ctx;\n \tconst bool was_enabled = READ_ONCE(kcsan_enabled);\n-\tu64 cycles;\n+\tktime_t nsecs;\n \n \t/* We may have been called from an atomic region; reset context. */\n \tmemset(¤t->kcsan_ctx, 0, sizeof(current->kcsan_ctx));\n@@ -70,16 +70,16 @@ static noinline void microbenchmark(unsi\n \n \tpr_info(\"%s begin | iters: %lu\\n\", __func__, iters);\n \n-\tcycles = get_cycles();\n+\tnsecs = ktime_get();\n \twhile (iters--) {\n \t\tunsigned long addr = iters & ((PAGE_SIZE << 8) - 1);\n \t\tint type = !(iters & 0x7f) ? KCSAN_ACCESS_ATOMIC :\n \t\t\t\t(!(iters & 0xf) ? KCSAN_ACCESS_WRITE : 0);\n \t\t__kcsan_check_access((void *)addr, sizeof(long), type);\n \t}\n-\tcycles = get_cycles() - cycles;\n+\tnsecs = ktime_get() - nsecs;\n \n-\tpr_info(\"%s end | cycles: %llu\\n\", __func__, cycles);\n+\tpr_info(\"%s end | nsecs: %llu\\n\", __func__, nsecs);\n \n \tWRITE_ONCE(kcsan_enabled, was_enabled);\n \t/* restore context */\n", "prefixes": [ "19/38" ] }