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Wed, 13 May 2026 02:22:58 -0700 (PDT) Received: from r912.lan.4v1.in ([182.70.116.80]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2baf1d27002sm167791555ad.8.2026.05.13.02.22.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 May 2026 02:22:58 -0700 (PDT) From: Avinash Duduskar To: netdev@vger.kernel.org Cc: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH net-next] llc: avoid sparse cast-truncates warning in counter clamps Date: Wed, 13 May 2026 14:52:53 +0530 Message-ID: <20260513092253.3035961-1-avinash.duduskar@gmail.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" llc_conn_ac_inc_npta_value() and llc_conn_ac_inc_tx_win_size() clamp their counters to the maximum valid 7-bit value via (u8) ~LLC_2_SEQ_NBR_MODULO. LLC_2_SEQ_NBR_MODULO is defined as ((u8) 128) in include/net/llc_pdu.h, but the (u8) cast does not prevent integer promotion of the operand of ~: ~128 is computed as int (0xffffff7f), and the surrounding (u8) cast truncates back to 0x7f. The result is correct (127), but the implicit truncation is flagged by sparse: net/llc/llc_c_ac.c:1008:38: warning: cast truncates bits from constant value (ffffff7f becomes 7f) (and three more at lines 1009, 1099, 1100) Replace the (u8) ~LLC_2_SEQ_NBR_MODULO expression with LLC_2_SEQ_NBR_MODULO - 1, which evaluates to 127 directly and silences sparse. The same ~LLC_2_SEQ_NBR_MODULO pattern also appears in include/net/llc_pdu.h:148 as part of PDU_GET_NEXT_Vr, but there the result is immediately &-masked, so the int promotion is harmless and sparse does not flag it; it is left alone. This patch is the minimum diff to silence the warning. The counter-clamp idiom itself could be modernized to min_t(u8, ..., LLC_2_SEQ_NBR_MODULO - 1), but that is a separate cleanup left for another patch. No functional change. Signed-off-by: Avinash Duduskar --- Built with CONFIG_LLC2=3Dm; full kernel build clean, sparse no longer warns on the touched lines. net/llc/llc_c_ac.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/net/llc/llc_c_ac.c b/net/llc/llc_c_ac.c index 0779daa8aa8f..ab86c720b3ec 100644 --- a/net/llc/llc_c_ac.c +++ b/net/llc/llc_c_ac.c @@ -1005,8 +1005,8 @@ static int llc_conn_ac_inc_npta_value(struct sock *sk= , struct sk_buff *skb) llc->dec_step =3D 0; llc->dec_cntr =3D llc->inc_cntr =3D 2; ++llc->npta; - if (llc->npta > (u8) ~LLC_2_SEQ_NBR_MODULO) - llc->npta =3D (u8) ~LLC_2_SEQ_NBR_MODULO; + if (llc->npta > LLC_2_SEQ_NBR_MODULO - 1) + llc->npta =3D LLC_2_SEQ_NBR_MODULO - 1; } else --llc->inc_cntr; return 0; @@ -1096,8 +1096,8 @@ int llc_conn_ac_inc_tx_win_size(struct sock *sk, stru= ct sk_buff *skb) struct llc_sock *llc =3D llc_sk(sk); =20 llc->k +=3D 1; - if (llc->k > (u8) ~LLC_2_SEQ_NBR_MODULO) - llc->k =3D (u8) ~LLC_2_SEQ_NBR_MODULO; + if (llc->k > LLC_2_SEQ_NBR_MODULO - 1) + llc->k =3D LLC_2_SEQ_NBR_MODULO - 1; return 0; } =20 base-commit: 8ebd24a7822cbae25beeafba49b2159d6a68a5f2 --=20 2.54.0