From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EB791430785 for ; Mon, 13 Jul 2026 13:46:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783950376; cv=none; b=VZwbC+8xwK5tt1Lg49Znoj6l4WFtA/MBpybSDGBygnpv9YNW5YOHaT3jslArr3TYV2dVr+Duf8fATF3SluhxQU1mYKo/P5FXXKNm80poXTwt/gR6JZxKsXpcy1weSB/H+UAROAUHM0osWbcDp+m9SfVOOgTBpEUMkzzA8HzbIyY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783950376; c=relaxed/simple; bh=Oa0Q1qNT1dXVjH+ViAMvtUdrDdzZgtwFLkPVXbBHXOM=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=LjymwxLvB/Ozpu4MRMmx8MxLEDfRcC4ZsciU0M+GPh4MiM5fI7nKUEes5tKIeCEWDbonO/gc4u/YjE8vUhyycz+jQAWxs4NxdIdPbsR/tEX5eu/PxoeJo/hpvFn/nhmRMAvzm2moP04MB51VeKnoK+W5iM5O1qDzQeJI1tfT2KY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=z2DIIpNf; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="z2DIIpNf" Received: by smtp.kernel.org (Postfix) with ESMTPSA id ECCA21F000E9; Mon, 13 Jul 2026 13:46:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1783950373; bh=I9x2nNVlF/CQ9OAMCsIC6JvnsR/9Bcf/3eBrzheuZcE=; h=Subject:To:Cc:From:Date; b=z2DIIpNfpuTuOywks24d5zzCCudfSDRQqlmFmXStuyCa42HPucv1QVdpqH/7PK4cw cXMKfPEqWGcwSN4t+oLxHKkiPJba3BX9xDvG14785ZUcOciLWMmQSIeWx1zs5TuHCM z38UToT1ZRCCto5ttM2mTYaT7hiU72w7IP72y0NY= Subject: FAILED: patch "[PATCH] coresight: etb10: restore atomic_t for shared reading state" failed to apply to 5.10-stable tree To: runyu.xiao@seu.edu.cn,james.clark@linaro.org,suzuki.poulose@arm.com Cc: From: Date: Mon, 13 Jul 2026 15:36:25 +0200 Message-ID: <2026071325-earthly-clothes-8ff0@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 5.10-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y git checkout FETCH_HEAD git cherry-pick -x fa09f08ede3db3050ae16ae1ed92c902d0cada23 # git commit -s git send-email --to '' --in-reply-to '2026071325-earthly-clothes-8ff0@gregkh' --subject-prefix 'PATCH 5.10.y' 'HEAD^..' Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From fa09f08ede3db3050ae16ae1ed92c902d0cada23 Mon Sep 17 00:00:00 2001 From: Runyu Xiao Date: Fri, 29 May 2026 00:52:01 +0800 Subject: [PATCH] coresight: etb10: restore atomic_t for shared reading state The etb10 miscdevice uses drvdata->reading as a shared exclusivity gate for userspace buffer access. etb_open() claims that gate with local_cmpxchg(), and etb_release() clears it with local_set(). That gate is shared per-device state rather than CPU-local state. A running system can reach it whenever /dev/ is opened, closed, and reopened by different tasks while the device remains registered, so the same drvdata->reading variable may be claimed on one CPU and later cleared on another. This code used to use atomic_t for the same gate, but commit 27b10da8fff2 ("coresight: etb10: moving to local atomic operations") changed it to local_t even though the access pattern remained cross-task and cross-CPU. Restore atomic_t together with atomic_cmpxchg() and atomic_set() so the exclusivity gate again uses a primitive intended for shared state. The issue was found on Linux v6.18.21 by our static analysis tool while scanning surviving local_t-on-shared-state sites, and then manually reviewed against the live etb10 file-op path. It was runtime-validated with a reproducible QEMU no-device KCSAN PoC that kept the same report-local contract: 1. use one shared struct etb_drvdata carrier and its drvdata->reading gate; 2. call etb_open() and etb_release() sequentially on that gate to confirm the original claim/clear path; 3. bind the open side to CPU0 and the release side to CPU1 for the same gate to show cross-CPU ownership; 4. run bound workers that repeatedly race etb_open() and etb_release() on the same gate until KCSAN reports a target hit. The harness recorded: L1 passed open=1 release=1 reading_after_open=1 reading_after_release=0 L2 passed open_cpu=0 release_cpu=1 cross_cpu_release=1 reading_after=0 open_ret=0 Representative KCSAN excerpt from the no-device validation run: BUG: KCSAN: data-race in etb_open.constprop.0.isra.0 [vuln_msv] write to 0xffffffffc0003810 of 4 bytes by task 216 on cpu 1: etb_open.constprop.0.isra.0+0x38/0x80 [vuln_msv] l3_worker_thread_fn+0x4f/0xf0 [vuln_msv] kthread+0x17e/0x1c0 ret_from_fork+0x22/0x30 read to 0xffffffffc0003810 of 4 bytes by task 215 on cpu 0: etb_open.constprop.0.isra.0+0x18/0x80 [vuln_msv] l3_worker_thread_fn+0x4f/0xf0 [vuln_msv] kthread+0x17e/0x1c0 ret_from_fork+0x22/0x30 value changed: 0x00000000 -> 0x00000001 Reported by Kernel Concurrency Sanitizer on: CPU: 0 PID: 215 Comm: etb10_l3_a Tainted: G O 6.1.66 #2 This no-device harness is not a real ETB10 hardware end-to-end run, but it preserves the same shared drvdata->reading gate and the same etb_open()/etb_release() claim/clear contract. No real ETB10 hardware was available for runtime testing. Build-tested with: make olddefconfig make -j"$(nproc)" drivers/hwtracing/coresight/coresight-etb10.o Fixes: 27b10da8fff2 ("coresight: etb10: moving to local atomic operations") Cc: stable@vger.kernel.org Signed-off-by: Runyu Xiao Reviewed-by: James Clark Signed-off-by: Suzuki K Poulose Link: https://lore.kernel.org/r/20260528165201.319452-1-runyu.xiao@seu.edu.cn diff --git a/drivers/hwtracing/coresight/coresight-etb10.c b/drivers/hwtracing/coresight/coresight-etb10.c index b952a1d47f12..a827f76b8144 100644 --- a/drivers/hwtracing/coresight/coresight-etb10.c +++ b/drivers/hwtracing/coresight/coresight-etb10.c @@ -83,7 +83,7 @@ struct etb_drvdata { struct coresight_device *csdev; struct miscdevice miscdev; raw_spinlock_t spinlock; - local_t reading; + atomic_t reading; pid_t pid; u8 *buf; u32 buffer_depth; @@ -601,7 +601,7 @@ static int etb_open(struct inode *inode, struct file *file) struct etb_drvdata *drvdata = container_of(file->private_data, struct etb_drvdata, miscdev); - if (local_cmpxchg(&drvdata->reading, 0, 1)) + if (atomic_cmpxchg(&drvdata->reading, 0, 1)) return -EBUSY; dev_dbg(&drvdata->csdev->dev, "%s: successfully opened\n", __func__); @@ -639,7 +639,7 @@ static int etb_release(struct inode *inode, struct file *file) { struct etb_drvdata *drvdata = container_of(file->private_data, struct etb_drvdata, miscdev); - local_set(&drvdata->reading, 0); + atomic_set(&drvdata->reading, 0); dev_dbg(&drvdata->csdev->dev, "%s: released\n", __func__); return 0;