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 64D0843C7DF for ; Wed, 15 Jul 2026 11:40:57 +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=1784115658; cv=none; b=fq7AFkN5QvmRZvkePtM1CTzXxmjrjlWOWbe77cOvGVxhATwZcbqODVvkchRSqpYZeTO/UkCmYzpL+yWWus+TZVB+zS0cg7FSEucfdYK3WH+Kk0cKhb+rDxH4s3jbJxCZ6WcBxglQxNKI3MVouJ8yCOtL852K+ckvo9bx1SxfERc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784115658; c=relaxed/simple; bh=yt3vKVXeFcUDAn6ddiTmk3lQl0xE6dIEjGp+LFCSq4E=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=XW0UEtQ67OwEm9iTbHZz6uzsqNN5B/ggBTPe8F7o5T9qSxudNrIxEJvEvVdFKtrBxQMbisSCrVOF/2082IJUsUGATX9uMjYay7Y6RXkUtUuOVyBPCCauDW+Fg3zcZZz5z67AqiIumZ+6ZcePBdWlk0ZgUDRqSmCqLIuWmjpdPgA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=BIAbf9sB; 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="BIAbf9sB" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6D22C1F00A3A; Wed, 15 Jul 2026 11:40:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784115657; bh=vbVXYwKqns8FptkaioibUYlxAvz6BA9DwrplP+SOKf8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=BIAbf9sBFKlsk+/BjlddOJWfiQojR+Xjx7ZesQZ2lUWwlyzONFIaxNPFms5BpzVjj kFEJCWgzPM++kic03ch7/gu02h13vqZJohdb6mSG9tNtXvovozH1Cun6w8F2NUnlMz PzNv55qhjXacu1kFt8kBhsVp0VI/iuO5TKYWVmgkRYEm0XswDkDR8/xbcrfD2V44Cq Dh7WFjIeksjdbP01AKQ5hLdSelhKtlLHzNjWf5/+6SiZkKE2ObNZkdr82WuziFzO2G +v+BzlDL8vBMGWmFe9pDN40jObDNJRnTIstZDAy1wUG+4HdSgxYTpY53nIdVpOhVfn 2VHUzh/tSR1dg== From: Sasha Levin To: stable@vger.kernel.org Cc: Runyu Xiao , James Clark , Suzuki K Poulose , Sasha Levin Subject: [PATCH 6.6.y] coresight: etb10: restore atomic_t for shared reading state Date: Wed, 15 Jul 2026 07:40:54 -0400 Message-ID: <20260715114054.728724-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026071323-clinking-armband-5963@gregkh> References: <2026071323-clinking-armband-5963@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 fa80039e0821f0..01ea3244cbdca9 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; @@ -604,7 +604,7 @@ 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__); @@ -642,7 +642,7 @@ 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