From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 91C6E2EA16A; Tue, 22 Jul 2025 13:52:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753192348; cv=none; b=NXj7EOsjcHFjGc/Icsuw3/VCUe3FDpwpxxdH+xqmyvS2AlOkRF7Bq02YzO9WAykiOXtuRTpR7u7zpcmRRJMsBvDA9hlue6WjZRGgsJFBMzgWO0Ds0ABA20+WQMDAmHfCviEiF/61jHfMioEBCX5cjK84ahXksbuHXWzeZYSLrog= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753192348; c=relaxed/simple; bh=0fo1TnrZrhHq2338lwMoyWuXELZPcx7vt5iUbpYYf8Y=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=KFu/wnxMdB81zJ0MRw18v83R19H9b6TGxbIvp+pzEL2bbgEHxSUGdfoM1Wn2P4N3/bgB2bHj2/+DhqIJHYgs0x/jc8aUEmCNr/iBJ488fukLqD8NdtpONa1wY9oYJx6ipAZtgDqKDo6jSD2Zr+BLpsavFpzTyvrAY6IrLoPVieU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Y16dfSB0; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="Y16dfSB0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EF8E2C4CEEB; Tue, 22 Jul 2025 13:52:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1753192348; bh=0fo1TnrZrhHq2338lwMoyWuXELZPcx7vt5iUbpYYf8Y=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Y16dfSB04q+FvXOX8fuWGpsHMniAG3kVUwfV23OCTMEJNaSKP+9s7VGLz7DiCEDMc xqu+ujrqc7JCOJ9zFysDsC8FDiWU4bZUBJEuP5BkYm2Dc75SyObv8obh8cqIn4Ro3Q zq85dBFP6iqlmzccJvq4XdjRYHaAnwumLbYf1cKw= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, stable@kernel.org, LongJun Tang , Yun Lu , Willem de Bruijn , "David S. Miller" Subject: [PATCH 6.6 032/111] af_packet: fix soft lockup issue caused by tpacket_snd() Date: Tue, 22 Jul 2025 15:44:07 +0200 Message-ID: <20250722134334.602295080@linuxfoundation.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250722134333.375479548@linuxfoundation.org> References: <20250722134333.375479548@linuxfoundation.org> User-Agent: quilt/0.68 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 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yun Lu commit 55f0bfc0370539213202f4ce1a07615327ac4713 upstream. When MSG_DONTWAIT is not set, the tpacket_snd operation will wait for pending_refcnt to decrement to zero before returning. The pending_refcnt is decremented by 1 when the skb->destructor function is called, indicating that the skb has been successfully sent and needs to be destroyed. If an error occurs during this process, the tpacket_snd() function will exit and return error, but pending_refcnt may not yet have decremented to zero. Assuming the next send operation is executed immediately, but there are no available frames to be sent in tx_ring (i.e., packet_current_frame returns NULL), and skb is also NULL, the function will not execute wait_for_completion_interruptible_timeout() to yield the CPU. Instead, it will enter a do-while loop, waiting for pending_refcnt to be zero. Even if the previous skb has completed transmission, the skb->destructor function can only be invoked in the ksoftirqd thread (assuming NAPI threading is enabled). When both the ksoftirqd thread and the tpacket_snd operation happen to run on the same CPU, and the CPU trapped in the do-while loop without yielding, the ksoftirqd thread will not get scheduled to run. As a result, pending_refcnt will never be reduced to zero, and the do-while loop cannot exit, eventually leading to a CPU soft lockup issue. In fact, skb is true for all but the first iterations of that loop, and as long as pending_refcnt is not zero, even if incremented by a previous call, wait_for_completion_interruptible_timeout() should be executed to yield the CPU, allowing the ksoftirqd thread to be scheduled. Therefore, the execution condition of this function should be modified to check if pending_refcnt is not zero, instead of check skb. - if (need_wait && skb) { + if (need_wait && packet_read_pending(&po->tx_ring)) { As a result, the judgment conditions are duplicated with the end code of the while loop, and packet_read_pending() is a very expensive function. Actually, this loop can only exit when ph is NULL, so the loop condition can be changed to while (1), and in the "ph = NULL" branch, if the subsequent condition of if is not met, the loop can break directly. Now, the loop logic remains the same as origin but is clearer and more obvious. Fixes: 89ed5b519004 ("af_packet: Block execution of tasks waiting for transmit to complete in AF_PACKET") Cc: stable@kernel.org Suggested-by: LongJun Tang Signed-off-by: Yun Lu Reviewed-by: Willem de Bruijn Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/packet/af_packet.c | 23 +++++++++++------------ 1 file changed, 11 insertions(+), 12 deletions(-) --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -2852,15 +2852,21 @@ static int tpacket_snd(struct packet_soc ph = packet_current_frame(po, &po->tx_ring, TP_STATUS_SEND_REQUEST); if (unlikely(ph == NULL)) { - if (need_wait && skb) { + /* Note: packet_read_pending() might be slow if we + * have to call it as it's per_cpu variable, but in + * fast-path we don't have to call it, only when ph + * is NULL, we need to check the pending_refcnt. + */ + if (need_wait && packet_read_pending(&po->tx_ring)) { timeo = wait_for_completion_interruptible_timeout(&po->skb_completion, timeo); if (timeo <= 0) { err = !timeo ? -ETIMEDOUT : -ERESTARTSYS; goto out_put; } - } - /* check for additional frames */ - continue; + /* check for additional frames */ + continue; + } else + break; } skb = NULL; @@ -2949,14 +2955,7 @@ tpacket_error: } packet_increment_head(&po->tx_ring); len_sum += tp_len; - } while (likely((ph != NULL) || - /* Note: packet_read_pending() might be slow if we have - * to call it as it's per_cpu variable, but in fast-path - * we already short-circuit the loop with the first - * condition, and luckily don't have to go that path - * anyway. - */ - (need_wait && packet_read_pending(&po->tx_ring)))); + } while (1); err = len_sum; goto out_put;