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 483C228725B for ; Wed, 15 Jul 2026 16:30:25 +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=1784133026; cv=none; b=IoyJ6a21E6LbOHtlAIlk0p+PY5yG/iijlleC6GDUC3pZqiqdLwlzdPuEcj2ccKHf/14fH2g7cHwR7aR1GudQ+8wqKt4fpS5mHA4ejVzk0PMELw1LqUFBh3cOkxLPvGUpA8Tw40F0qG8uKGQGE0Dha1rScqB21CX3NOHNxPoSQpQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784133026; c=relaxed/simple; bh=moPdQxzyaIDYjzOacpxcu40QF/X/9OYEZgi97wmvWJE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=QRtpT/HaoYh2t3XQAJPcHN95jmoHEJGrBZ4rvo5Tdy93pZXRrCaG7wwiPk1kyrw4MADDOvUNH7Eb7u1VRLHnhzR+p8Ii9iw7yONMIxUuztiCkTdqVCKciBqJ9NRkmseOM4cvOFGBa4krUzGpIrHpn9ePINwVeRnly6DdxlSz8vE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SpA27K+Q; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="SpA27K+Q" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 519B11F000E9; Wed, 15 Jul 2026 16:30:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784133024; bh=q/aldqVZpTg0JLZwPrvwr0RXlMrT6zFXrJzMDMafxqQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=SpA27K+QR4gAC+HG8DxvbG2PArFqwXIZixvokalCF96ILxi8f1caDsIZ/ok1IR7Hu Sk7Kn0bUwGFYGsA5PYYgDDQH5kIrUYmGoEkMnKQPRF4d15ONDGA8ORDJ7U4ijgy3nB QudZk+riX2THYF5YN6d8AsgpwnwJR+IjxyUDizksbYYsFcYUkMGyU3wDtXSWNkR8Y/ 1YoSE5rpIyPBvZqIewYKvYvbFCIBDSDf8OPeTRPLnCVr6Ktis43OoaOBxN7yl32K28 cMpSf6Nugw+ou0VV/MZkJrlr2ItDUmwdpy6FTgM90dTe3fwu5bnDrBbGC59xiMK3Dk I7htyEjT5NYsg== From: Sasha Levin To: stable@vger.kernel.org Cc: Runyu Xiao , James Clark , Suzuki K Poulose , Sasha Levin Subject: [PATCH 6.1.y] coresight: etb10: restore atomic_t for shared reading state Date: Wed, 15 Jul 2026 12:30:22 -0400 Message-ID: <20260715163022.950711-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026071324-animosity-zone-6759@gregkh> References: <2026071324-animosity-zone-6759@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Runyu Xiao [ Upstream commit fa09f08ede3db3050ae16ae1ed92c902d0cada23 ] 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: Sasha Levin --- drivers/hwtracing/coresight/coresight-etb10.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/hwtracing/coresight/coresight-etb10.c b/drivers/hwtracing/coresight/coresight-etb10.c index 8aa6e4f83e42b5..d73b2dec6937d7 100644 --- a/drivers/hwtracing/coresight/coresight-etb10.c +++ b/drivers/hwtracing/coresight/coresight-etb10.c @@ -86,7 +86,7 @@ struct etb_drvdata { struct coresight_device *csdev; struct miscdevice miscdev; spinlock_t spinlock; - local_t reading; + atomic_t reading; pid_t pid; u8 *buf; u32 mode; @@ -603,7 +603,7 @@ 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__); @@ -641,7 +641,7 @@ 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; -- 2.53.0