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Tue, 18 Aug 2026 00:23:25 -0700 (PDT) X-Received: by 2002:a17:90b:524b:b0:37f:bfa2:1887 with SMTP id 98e67ed59e1d1-3933cb3f7d3mr34521438a91.8.1787037805386; Tue, 18 Aug 2026 00:23:25 -0700 (PDT) Received: from [10.239.97.207] ([114.94.8.21]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-39339d00eafsm6844315a91.1.2026.08.18.00.23.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 18 Aug 2026 00:23:25 -0700 (PDT) Message-ID: <53126b4a-09a9-443b-bfb5-e7285494aa7a@oss.qualcomm.com> Date: Tue, 18 Aug 2026 15:23:20 +0800 Precedence: bulk X-Mailing-List: linux-serial@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] tty: n_tty: use kvzalloc/kvfree for line discipline data To: Jiri Slaby , gregkh@linuxfoundation.org Cc: linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, stable@vger.kernel.org, liulzhao@qti.qualcomm.com, cheng.jiang@oss.qualcomm.com, cxin@qti.qualcomm.com References: <20260817135526.386863-1-xin.chen2@oss.qualcomm.com> <20260818070324.136726-1-xin.chen2@oss.qualcomm.com> <2e072c67-9d42-409a-8c24-82e88dd01418@kernel.org> From: Xin Chen In-Reply-To: <2e072c67-9d42-409a-8c24-82e88dd01418@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Proofpoint-ORIG-GUID: 00de-S7VHK4WPKwx0LYzBofZEMMCgRYO X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODE4MDA1MiBTYWx0ZWRfX1N/5cTJvzWDs Z1pgZcTwv1OEKayFaJa3qj4g3yxy77gWGza2gJnyMy33uKaaGRa/3P6FUvBM6BmQnoepLU6hMQn gnvAfx/5djKe/oNxhVD6KefEEuodqvW2JgClBZQHFK3NhXzPkYmqXuxmi0n75JK0q9j/T8iU8me zCXgvnljzs00AfRoQQMfsFUlCrHcn32PXJNizsD7VOu/XdlZdujQ5OQNblhv+mU2cvLYjL/g+6L r2wNSInnMfKxvHPWjV5bjnTevONL+liYtNDMMDc9w8KxxV8F6dSUngHbhijYqHcYkPJBEK59/GN QKmSKwQo+jN9NZY8WyKcEVU6cIXdX+y8F96l5q0myoRSBLTnfvSsuYrIqdSyYun13nR6YpcHNqc MPQIDyqV3xnvtuKz+BFa4UrFPV8PPdUGNUR2TEWMXvmAIzy2ch4n9PAqo2AmBzmP/yzx9XEZDr0 hixxiOYiZUY6Les+nVA== X-Authority-Analysis: v=2.4 cv=K/IS2SWI c=1 sm=1 tr=0 ts=6a84086e cx=c_pps a=RP+M6JBNLl+fLTcSJhASfg==:117 a=Uz3yg00KUFJ2y2WijEJ4bw==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=3WHJM1ZQz_JShphwDgj5:22 a=tjhzb4fLYD-Z8NmU190A:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=iS9zxrgQBfv6-_F4QbHw:22 X-Proofpoint-Spam-Info: AW1haW4tMjYwODE4MDA1MiBTYWx0ZWRfXzAufpFDg8i87 +ETqZLYSZtmuaHohMIkLlP3xA1G0+5WF9ZclihdjesrYREZMJnb+Lp9AMKabAM2diNaq7HzVs40 5ZG7McjrQ81MFbJRpFYLF9gy7Xs2xdM= X-Proofpoint-GUID: 00de-S7VHK4WPKwx0LYzBofZEMMCgRYO X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-17_04,2026-08-12_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 suspectscore=0 clxscore=1015 impostorscore=0 lowpriorityscore=0 bulkscore=0 spamscore=0 priorityscore=1501 adultscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608180052 On Tue, Aug 18, 2026, Jiri Slaby wrote: > Switching from order-0 to order-2? If you ran out of vmspace on some > 32bit platform, perhaps. But you apparently did not. So all this > feels odd. To clarify: the concern is not vmalloc address space exhaustion. The issue is that vzalloc() allocates order-0 pages from the buddy allocator via the bulk allocation path (alloc_pages_bulk_noprof), which uses ALLOC_WMARK_LOW and does not perform direct reclaim. When two back-to-back vzalloc() calls drain enough order-0 pages to push the zone below the low watermark, a subsequent skb_clone(GFP_KERNEL) in hci_send_cmd_sync() fails silently, leaving hdev->req_skb NULL and causing BT enable to time out with -ETIMEDOUT. kvzalloc_obj() serves the ~10 KB n_tty_data from the kmalloc-16384 slab, which is backed by order-2 compound pages — a separate pool that does not deplete the order-0 free list that skb_clone() depends on.  The commit message could have been clearer on this point; I will improve it in the next version. Thanks, Xin Chen