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 B650542A17B; Thu, 16 Jul 2026 14:25:26 +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=1784211928; cv=none; b=pDrigDw76F1i0EezpNA1sPmGmu0f/cySwYnvcbP9hyBbv2RD0Kd89wUK9u3a1fLxZ35QqVL7BtXYki9zhaz+AJ8cmWApHEddNCnS1tsoPVVo4VWHVQNWPfvlJjAgxuJ7LH+5WAt4Epl7vKuc2bq0NDQNqrVOod19cyyYibpoYTQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784211928; c=relaxed/simple; bh=PqVkLcpxcUgr8SU5Xmz4memy7qpX6aat8kr9AGmut6U=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=kk1aFssSazGN2rckYb8TXIxuxIDxxVDcRPoB1qZ3aHV6anEtihciBNIk/dlGvsrf6wZsOVxelUYEmsqQvlkhCupxMW9OB+5JjjVD8/z/G8nvCaE11ShNmUN9/ib1zlXPdgLLii2pyGdrFptEPogs5DaXsd1QiqRlIiNIIMtpFAI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Y1AyxQar; 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="Y1AyxQar" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 268B31F000E9; Thu, 16 Jul 2026 14:25:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1784211926; bh=0bR9aqGlFuY5Kc0A+pUfE3aSz0RrEsklQuKIH+kX79Q=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Y1AyxQartj5cL9R6Uk0KOCuKst6HhQzMdf7B/LCb/3ig7DvEJ27RTjzWtxNv8a4no 4pPIcHfTJTLlA88uHwwk5qDCbpP/1rGcM2JDx+w6SXoJdb2O1gntN5hzZtnCUaIfEV Oble+iTCYkpgidppicj6xek41TkVHk9/bbBEAeIU= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Runyu Xiao , James Clark , Suzuki K Poulose Subject: [PATCH 6.12 132/349] coresight: etb10: restore atomic_t for shared reading state Date: Thu, 16 Jul 2026 15:31:06 +0200 Message-ID: <20260716133036.319712218@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260716133033.287196923@linuxfoundation.org> References: <20260716133033.287196923@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Runyu Xiao commit fa09f08ede3db3050ae16ae1ed92c902d0cada23 upstream. 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 Signed-off-by: Greg Kroah-Hartman --- drivers/hwtracing/coresight/coresight-etb10.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/drivers/hwtracing/coresight/coresight-etb10.c +++ b/drivers/hwtracing/coresight/coresight-etb10.c @@ -85,7 +85,7 @@ 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; @@ -603,7 +603,7 @@ static int etb_open(struct inode *inode, 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__); @@ -641,7 +641,7 @@ static int etb_release(struct inode *ino { 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;