From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mo4-p02-ob.smtp.rzone.de (mo4-p02-ob.smtp.rzone.de [85.215.255.82]) (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 96E1E3C76A6 for ; Fri, 24 Jul 2026 08:39:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=pass smtp.client-ip=85.215.255.82 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784882346; cv=pass; b=h2mkQDjsnChYuVbvJpozEOnfFhDq7EMhXIOgKPv0R1z5I1SaGrM6ePGSgp+tVsMNWjvFSsrsOygRYqmZK1ialg7vXVw619d4Q4fnCl0TDIC6RyBrNwnM4qhxyebRIVtS1fJDAejBKTVU9gsdBEnh9bLpQHr2a5fikaA5T3IaSc8= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784882346; c=relaxed/simple; bh=n4mIYpVwgXfoP+it1cq45fgFfDXBtjqv/PorSWhrl7E=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=umRtbkpaP8Ex9/jQZdW31ibxflELBlb1GsK3eKh2n35h+SEDZ7Zhbi/q4G12aDGHDzPYsW09bMqOVnIB7HeI6WqSlrcPEJl8SjmL+ZbCPc9vYC0cHS0K8Wxb/9Ww9iDdVoNUCALWrh/6FlB4nRHyDJKsecYHrm//PHpUTk6CRw8= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=hartkopp.net; spf=fail smtp.mailfrom=hartkopp.net; dkim=pass (2048-bit key) header.d=hartkopp.net header.i=@hartkopp.net header.b=kMmcUc7c; dkim=permerror (0-bit key) header.d=hartkopp.net header.i=@hartkopp.net header.b=h/gTTcHX; arc=pass smtp.client-ip=85.215.255.82 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=hartkopp.net Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=hartkopp.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=hartkopp.net header.i=@hartkopp.net header.b="kMmcUc7c"; dkim=permerror (0-bit key) header.d=hartkopp.net header.i=@hartkopp.net header.b="h/gTTcHX" ARC-Seal: i=1; a=rsa-sha256; t=1784882341; cv=none; d=strato.com; s=strato-dkim-0002; b=ZHAWW4Q2gfhe35NZcJ3Uv2ITE6b3++D52onMwIunRaUPbWRBAWEN4ixke4ESn8glfj m8lzLBS59xjsWnLwg9BhPGxCEfvDNJiwKH/o02Yf7kVaLLSEb5gEHCdhxHHVVL3NaExP PJREwViTNQ9rXLieEu/XmumRqQiGjs54dQQU7wXU45PUw2F5v+hXwu4ien2ZNm2k+X+N /gbhCkrX1HU55fP2N30mG5LFhBtEMGDe7iPczkvCQ6MEF2GPTR89h+jQ0qZUB9b5cYws EbFc2Z6QQd0cTSXDmIC4IvoUQEYFVwXqYaZJbXzUbycjvh5P8UPQRaqRhC5p7e37NO92 3rqA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; t=1784882341; s=strato-dkim-0002; d=strato.com; h=References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From:Cc:Date: From:Subject:Sender; bh=+5CGd8nR5DBrkWQSbmek/90YFDpPOn7fZCqP21O1uZc=; b=Ldu7xzn4cDOX4ucBmqMf2DLJt7R77AWCJB+isOvOdL5k86A+ryiGK9Jr8O7qhRY51L GufEqbWQPPgWZNQ4XLMOvw7U2c1vlyF1XKVuLnBQz2Bo0HosGu0W36b1WNTbF5R6y7AK /IFWPZ/VJM8Q27YZpteUjfiiIjUP9WmhF1/x99MUJXJvSRItOx3R3AZWF09b39OkfqJp axiC6BqmntF3wGXgj5uo45TFppQVfEqPsKzGS6N2TLcvlMo8HYSrvagcn/h8OvE9UKDh Bc09J4swlDUUhbRSuEpVMrU8dPQNp88/FDNL444xPNMywiUQYnt1y+92H32Hbyqe8sDA IwSw== ARC-Authentication-Results: i=1; strato.com; arc=none; dkim=none X-RZG-CLASS-ID: mo02 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; t=1784882341; s=strato-dkim-0002; d=hartkopp.net; h=References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From:Cc:Date: From:Subject:Sender; bh=+5CGd8nR5DBrkWQSbmek/90YFDpPOn7fZCqP21O1uZc=; b=kMmcUc7cJII/qWfHiMdxAmYWXWiBsfOqTjnikDiMnQ0Kk1QUbHoZHqPVYrrWjqGdwl ArCqXrnQx3KkZFaZjfNfpET1HNOP06iOQLGkG1ikhJE2B3N/CSuIGaYFNd+XhaP21owT hlA3fn5bHDrBNh3blSYz9n56inmvbsDTE/jzOqglpfAdcW4TCLmbbaGZ82kBCQ1HDpXu F+weqvDA+fHZSkBmEFZOzUjmBouxRnhnTjSqnycofvXZ+Ued/QdKnPm2BvraVJf0EoDJ GKPecT2Xia/BdP+kiJCN85CrFKZwSa9R3JkjHRFjP9Q9HE50hy/Rcre2DcIsCHg1mx4D zJBA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; t=1784882341; s=strato-dkim-0003; d=hartkopp.net; h=References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From:Cc:Date: From:Subject:Sender; bh=+5CGd8nR5DBrkWQSbmek/90YFDpPOn7fZCqP21O1uZc=; b=h/gTTcHX3MvVTSYOHmu90wU8nAsTa624WdGOssRIx73Fw5PFBzE25Ek83zhILH+j/E KbwnzGv3N+x9WkdKkJCQ== X-RZG-AUTH: ":P2MHfkW8eP4Mre39l357AZT/I7AY/7nT2yrDxb8mjH4JKvMdQv2tRkI16oOSW1Ti/f4PoH8=" Received: from vivo.lan by smtp.strato.de (RZmta 55.5.6 SBL|AUTH) with ESMTPSA id K5281926O8d1rT0 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256 bits)) (Client did not present a certificate); Fri, 24 Jul 2026 10:39:01 +0200 (CEST) From: Oliver Hartkopp To: stable@vger.kernel.org Cc: Oliver Hartkopp , Marc Kleine-Budde Subject: [PATCH 2/8] can: bcm: fix CAN frame rx/tx statistics Date: Fri, 24 Jul 2026 10:38:45 +0200 Message-ID: <20260724083851.12603-3-socketcan@hartkopp.net> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026072046-absolve-unsorted-3f5d@gregkh> References: <2026072046-absolve-unsorted-3f5d@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="us-ascii" commit e6c24ba95fc3f1b5e1dcd28b1c6e59ef61a9daa5 upstream. KCSAN detected a data race within the bcm_rx_handler() when two CAN frames have been simultaneously received and processed in a single rx op by two different CPUs. Use atomic operations with (signed) long data types to access the statistics in the hot path to fix the KCSAN complaint. Additionally simplify the update and check of statistics overflow by using the atomic operations in separate bcm_update_[rx|tx]_stats() functions. The rx variant runs under bcm_rx_update_lock to prevent races when resetting the two rx counters; the tx variant runs under bcm_tx_lock and only needs to guard its own counter's overflow. As the rx path resets its values already at LONG_MAX / 100, there is no conflict between the two locking domains (bcm_rx_update_lock vs. bcm_tx_lock) even for ops that use both paths. The rx statistics update and the frames_filtered update in bcm_rx_changed() were previously performed in two separate bcm_rx_update_lock sections. For an rx op subscribed on all interfaces (ifindex == 0), bcm_rx_handler() can run concurrently on different CPUs, so a counter reset by one CPU between these two sections could leave frames_filtered larger than frames_abs on another CPU, producing a bogus (even negative) reduction percentage in procfs. Update the statistics in the same critical section as bcm_rx_changed() to close this gap, which also removes the now unneeded extra lock/unlock pair around the traffic_flags calculation. Fixes: ffd980f976e7 ("[CAN]: Add broadcast manager (bcm) protocol") Signed-off-by: Oliver Hartkopp Link: https://patch.msgid.link/20260714-bcm_fixes-v15-4-562f7e3e42da@hartkopp.net Cc: stable@kernel.org Signed-off-by: Marc Kleine-Budde Signed-off-by: Oliver Hartkopp --- net/can/bcm.c | 67 +++++++++++++++++++++++++++++++++++++++-------------------- 1 file changed, 45 insertions(+), 22 deletions(-) diff --git a/net/can/bcm.c b/net/can/bcm.c index fccb573..2ce83f8 100644 --- a/net/can/bcm.c +++ b/net/can/bcm.c @@ -109,7 +109,7 @@ struct bcm_op { int ifindex; canid_t can_id; u32 flags; - unsigned long frames_abs, frames_filtered; + atomic_long_t frames_abs, frames_filtered; struct bcm_timeval ival1, ival2; struct hrtimer timer, thrtimer; ktime_t rx_stamp, kt_ival1, kt_ival2, kt_lastmsg; @@ -216,10 +216,13 @@ static int bcm_proc_show(struct seq_file *m, void *v) list_for_each_entry_rcu(op, &bo->rx_ops, list) { - unsigned long reduction; + long reduction, frames_filtered, frames_abs; + + frames_filtered = atomic_long_read(&op->frames_filtered); + frames_abs = atomic_long_read(&op->frames_abs); /* print only active entries & prevent division by zero */ - if (!op->frames_abs) + if (!frames_abs) continue; seq_printf(m, "rx_op: %03X %-5s ", op->can_id, @@ -241,9 +244,9 @@ static int bcm_proc_show(struct seq_file *m, void *v) (long long)ktime_to_us(op->kt_ival2)); seq_printf(m, "# recv %ld (%ld) => reduction: ", - op->frames_filtered, op->frames_abs); + frames_filtered, frames_abs); - reduction = 100 - (op->frames_filtered * 100) / op->frames_abs; + reduction = 100 - (frames_filtered * 100) / frames_abs; seq_printf(m, "%s%ld%%\n", (reduction == 100) ? "near " : "", reduction); @@ -267,7 +270,8 @@ static int bcm_proc_show(struct seq_file *m, void *v) seq_printf(m, "t2=%lld ", (long long)ktime_to_us(op->kt_ival2)); - seq_printf(m, "# sent %ld\n", op->frames_abs); + seq_printf(m, "# sent %ld\n", + atomic_long_read(&op->frames_abs)); } seq_putc(m, '\n'); @@ -277,6 +281,24 @@ static int bcm_proc_show(struct seq_file *m, void *v) } #endif /* CONFIG_PROC_FS */ +static void bcm_update_rx_stats(struct bcm_op *op) +{ + /* prevent overflow of the reduction% calculation in bcm_proc_show() */ + if (atomic_long_inc_return(&op->frames_abs) > LONG_MAX / 100) { + atomic_long_set(&op->frames_filtered, 0); + atomic_long_set(&op->frames_abs, 0); + } +} + +static void bcm_update_tx_stats(struct bcm_op *op) +{ + /* tx_op has no reduction% calculation - use the full range and + * just keep the displayed counter non-negative on overflow + */ + if (atomic_long_inc_return(&op->frames_abs) == LONG_MAX) + atomic_long_set(&op->frames_abs, 0); +} + /* * bcm_can_tx - send the (next) CAN frame to the appropriate CAN interface * of the given bcm tx op @@ -328,7 +350,7 @@ static void bcm_can_tx(struct bcm_op *op, struct canfd_frame *cf) spin_lock_bh(&op->bcm_tx_lock); if (!err) - op->frames_abs++; + bcm_update_tx_stats(op); /* only advance the cyclic sequence if nothing reset currframe while * we were sending - a concurrent TX_RESET_MULTI_IDX means this @@ -473,12 +495,9 @@ static void bcm_rx_changed(struct bcm_op *op, struct canfd_frame *data) { struct bcm_msg_head head; - /* update statistics */ - op->frames_filtered++; - - /* prevent statistics overflow */ - if (op->frames_filtered > ULONG_MAX/100) - op->frames_filtered = op->frames_abs = 0; + /* update statistics (frames_filtered <= frames_abs) */ + if (atomic_long_read(&op->frames_abs)) + atomic_long_inc(&op->frames_filtered); /* this element is not throttled anymore */ data->flags &= (BCM_CAN_FLAGS_MASK|RX_RECV); @@ -718,25 +737,29 @@ static void bcm_rx_handler(struct sk_buff *skb, void *data) op->rx_stamp = skb->tstamp; /* save originator for recvfrom() */ op->rx_ifindex = skb->dev->ifindex; - /* update statistics */ - op->frames_abs++; - /* snapshot the flag under lock: op->flags/op->frames may be updated - * concurrently by bcm_rx_setup(). - */ + /* op->flags/op->frames may be updated concurrently by bcm_rx_setup() */ spin_lock_bh(&op->bcm_rx_update_lock); + rtr_frame = op->flags & RX_RTR_FRAME; - if (rtr_frame) + if (rtr_frame) { + bcm_update_rx_stats(op); + /* snapshot RTR content under lock */ memcpy(&rtrframe, op->frames, op->cfsiz); - spin_unlock_bh(&op->bcm_rx_update_lock); + spin_unlock_bh(&op->bcm_rx_update_lock); - if (rtr_frame) { /* send reply for RTR-request (placed in op->frames[0]) */ bcm_can_tx(op, &rtrframe); return; } - spin_lock_bh(&op->bcm_rx_update_lock); + /* update statistics in the same critical section as bcm_rx_changed() + * below: frames_filtered must never be checked/incremented against a + * frames_abs snapshot from a concurrent bcm_rx_handler() call on + * another CPU for the same (wildcard) op, or frames_filtered can end + * up larger than frames_abs. + */ + bcm_update_rx_stats(op); if (op->flags & RX_FILTER_ID) { /* the easiest case */ -- 2.43.0