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 A3067349AFF; Wed, 20 May 2026 17:50:16 +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=1779299417; cv=none; b=SCiXC6QGVLEL6QDohRshdZEbKlsVvaoWucaNsMCFFuVlag2jxYvJob0M3lXC/YJT3Qvp+rNRDsooZbejFd0LyBqftX6McTPerINytns0KXZM+axWKAyJ2vNkAsmpFAP/9SjqOXdObnAKJe+0PUS7qdgv65tjqUUXMjJup52IG3I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779299417; c=relaxed/simple; bh=M4lOwg/xZ13mqxH8CYLxgDiuC1WgrGZC/Xx5cokHzbo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Ks1ikLGFrpc4i7j82Tjn1crVBWAdgEPu/2JZoo90vPqnF0Fumqbx4xkTpXSdEr6QtLuPWS9WKpNufrh8W5inqEOvxJg5wlImcKZwNy5y4Y1aTLzanDnGYn8NWySDPofFioGP2E4w5Wh5JSoya6zf7IIBlx7/olB+P1CwNG+XFqg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=10TjWN18; 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="10TjWN18" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CB9221F000E9; Wed, 20 May 2026 17:50:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1779299416; bh=JKqKawmZJpbx7Y1dIX/jVcwWbPRclydU8H4XbIMqzKU=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=10TjWN18nQyoBbpiS9i94pOgNsMDDXmOAjCmhDSFADnCT+aYIdTC/XPoaRR/9i+10 eKirHuk+DOn9MgYIxpPx+xCO6m4EQKkK/S5uTLBeUzlzgtKhj6qHg7ARoTc3qVkBV8 hjp4hxI7QcJEAjodN+bQpYxm7ujrmF/z9KTIzdlg= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Stephen Hemminger , Simon Horman , Jakub Kicinski , Sasha Levin Subject: [PATCH 6.18 765/957] net/sched: netem: fix probability gaps in 4-state loss model Date: Wed, 20 May 2026 18:20:48 +0200 Message-ID: <20260520162151.154003996@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260520162134.554764788@linuxfoundation.org> References: <20260520162134.554764788@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 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Stephen Hemminger [ Upstream commit 732b463449fd0ef90acd13cda68eab1c91adb00c ] The 4-state Markov chain in loss_4state() has gaps at the boundaries between transition probability ranges. The comparisons use: if (rnd < a4) else if (a4 < rnd && rnd < a1 + a4) When rnd equals a boundary value exactly, neither branch matches and no state transition occurs. The redundant lower-bound check (a4 < rnd) is already implied by being in the else branch. Remove the unnecessary lower-bound comparisons so the ranges are contiguous and every random value produces a transition, matching the GI (General and Intuitive) loss model specification. This bug goes back to original implementation of this model. Fixes: 661b79725fea ("netem: revised correlated loss generator") Signed-off-by: Stephen Hemminger Reviewed-by: Simon Horman Link: https://patch.msgid.link/20260418032027.900913-2-stephen@networkplumber.org Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/sched/sch_netem.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c index 6f8fcc4b504ce..4eb6ed60ee9b6 100644 --- a/net/sched/sch_netem.c +++ b/net/sched/sch_netem.c @@ -227,10 +227,10 @@ static bool loss_4state(struct netem_sched_data *q) if (rnd < clg->a4) { clg->state = LOST_IN_GAP_PERIOD; return true; - } else if (clg->a4 < rnd && rnd < clg->a1 + clg->a4) { + } else if (rnd < clg->a1 + clg->a4) { clg->state = LOST_IN_BURST_PERIOD; return true; - } else if (clg->a1 + clg->a4 < rnd) { + } else { clg->state = TX_IN_GAP_PERIOD; } @@ -247,9 +247,9 @@ static bool loss_4state(struct netem_sched_data *q) case LOST_IN_BURST_PERIOD: if (rnd < clg->a3) clg->state = TX_IN_BURST_PERIOD; - else if (clg->a3 < rnd && rnd < clg->a2 + clg->a3) { + else if (rnd < clg->a2 + clg->a3) { clg->state = TX_IN_GAP_PERIOD; - } else if (clg->a2 + clg->a3 < rnd) { + } else { clg->state = LOST_IN_BURST_PERIOD; return true; } -- 2.53.0