From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-23.mta0.migadu.com [91.218.175.23]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 301E13AA9E2 for ; Tue, 8 Sep 2026 08:08:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.23 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788854892; cv=none; b=pTi6aaA1UxfgATDKgfIO+rnl8YEZerm27FSxFSZHuh+zER3J8lbon+STdsgKkaQtwPinrEAvjNpGn9hhDQ1L325T+FWIDUzQM0vsVADwGQhyA+oxat/g9m9wS6sPlkLtn0XP2qM97xj79kx0FQP/cY5YXOsg3DSGF8cLXM6UCtc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788854892; c=relaxed/simple; bh=17Qpr2HZAfjTf+fUY0bEYiBsyBtJXKQkXqw9F9jXj84=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=BqWhU9cprP341NymGWUGAsNo4aZozegq915BHFZA7RKM/BPg01pJrVplNIxab6edFrMnsyxEnxxHZvw0agUNPY6JPIH2WH0DCfa8UanhGkxCfppASvslTxA+wVvHZq4sFPuJH798+tuq99/xlek7sj5kTt2tJM0cblzFc2ptx6w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=YhKPa69D; arc=none smtp.client-ip=91.218.175.23 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="YhKPa69D" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=17Qpr2HZAfjTf+fUY0bEYiBsyBtJXKQkXqw9F9jXj84=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1788854886; v=1; x=1789459686; b=YhKPa69DdS5qZIl1G+SGZx4cR2YVxx0k6mS3QpgPwciPPwYelLamurWlQsD5W+ZQZsA6u7g1 IrmvqGHkQNvFrE/Bum+vIYjfi6jVrBlqGmZYwySvi8xOekOZMLm8guERo+N5LfGFU7f0zQoNeR8 M36VdzpZO26Hl6or04k7N/xM= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id f75abea937d6cb6f; Tue, 08 Sep 2026 08:08:06 +0000 X-Mizu-Trace-ID: f75abea937d6cb6f X-Migadu-Flow: FLOW_OUT Message-ID: Date: Tue, 8 Sep 2026 16:07:48 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH bpf v2 2/3] tcp: Skip cond_resched() in inet_csk_listen_stop() under BPF context To: Kuniyuki Iwashima , bot+bpf-ci@kernel.org Cc: bpf@vger.kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com, sdf@fomichev.me, martin.lau@linux.dev, ast@kernel.org, andrii@kernel.org, eddyz87@gmail.com, memxor@gmail.com, song@kernel.org, yonghong.song@linux.dev, jolsa@kernel.org, emil@etsalapatis.com, ihor.solodrai@linux.dev, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, ncardwell@google.com, shuah@kernel.org, aditi.ghag@isovalent.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, martin.lau@kernel.org, mason@kernel.org References: <20260906074135.185212-3-jiayuan.chen@linux.dev> <0aa6425f9e8f32705ae827f6325b29079234c3f3d0c7b2cdefba3e5b50432766@mail.kernel.org> From: Jiayuan Chen In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 9/8/26 7:34 AM, Kuniyuki Iwashima wrote: > On Sun, Sep 6, 2026 at 1:23 AM wrote: >>> tcp: Skip cond_resched() in inet_csk_listen_stop() under BPF context >>> >>> bpf_sock_destroy() runs from the tcp iterator, under rcu_read_lock(). If >>> the sock is a listener that still has children in its accept queue, >>> tcp_abort() ends up in inet_csk_listen_stop() and the cond_resched() >>> there trips the debug check: >>> >>> BUG: sleeping function called from invalid context at net/ipv4/inet_connection_sock.c:1523 >>> in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 628, name: test_progs >>> preempt_count: 0, expected: 0 >>> RCU nest depth: 1, expected: 0 >>> locks held by test_progs/628: 3, last CPU#3: >>> #0: ffff8881158cee18 (&p->lock){+.+.}-{4:4}, at: bpf_seq_read+0x56/0x1210 >>> #1: ffff8881106bb858 (sk_lock-AF_INET6){+.+.}-{0:0}, at: bpf_iter_tcp_seq_show+0x32b/0x4b0 >>> #2: ffffffffb435af20 (rcu_read_lock){....}-{1:3}, at: bpf_iter_run_prog+0x46b/0xde0 >>> CPU: 3 UID: 0 PID: 628 Comm: test_progs Tainted: G W 7.2.0+ #65 PREEMPT >>> Tainted: [W]=WARN >>> Call Trace: >>> >>> dump_stack_lvl+0xc1/0xf0 >>> dump_stack+0x10/0x20 >>> __might_resched+0x3d2/0x610 >>> inet_csk_listen_stop+0x7b/0xbf0 >>> tcp_abort+0x23b/0x3b0 >>> bpf_sock_destroy+0xfc/0x140 >>> bpf_prog_448133d24601754f_iter_tcp6_server+0x81/0x8a >>> bpf_iter_run_prog+0x538/0xde0 >>> bpf_iter_tcp_seq_show+0x26b/0x4b0 >>> bpf_seq_read+0x424/0x1210 >>> vfs_read+0x197/0xe40 >>> ksys_read+0x119/0x240 >>> __x64_sys_read+0x72/0xc0 >>> x64_sys_call+0x647/0x27e0 >>> do_syscall_64+0xe5/0x610 >>> entry_SYSCALL_64_after_hwframe+0x76/0x7e >>> RIP: 0033:0x7fad39b28aca >>> RSP: 002b:00007ffc381c61c0 EFLAGS: 00000246 ORIG_RAX: 0000000000000000 >>> RAX: ffffffffffffffda RBX: 00007ffc381c6a88 RCX: 00007fad39b28aca >>> RDX: 0000000000000032 RSI: 00007ffc381c6250 RDI: 0000000000000014 >>> RBP: 00007ffc381c61e0 R08: 0000000000000000 R09: 0000000000000000 >>> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003 >>> R13: 0000000000000000 R14: 000055f077c1bbb0 R15: 00007fad3a0f3000 >>> >>> >>> The commit that added the kfunc already guards lock_sock() in tcp_abort() >>> and udp_abort() with has_current_bpf_ctx(), but missed the listener path. >>> Do the same for the cond_resched(), it can't reschedule there anyway. >>> >>> Fixes: 4ddbcb886268 ("bpf: Add bpf_sock_destroy kfunc") >>> Signed-off-by: Jiayuan Chen >> Is the justification "it can't reschedule there anyway" accurate? >> >> With CONFIG_PREEMPT_DYNAMIC=y booted with preempt=none or preempt=voluntary, >> cond_resched() expands to __cond_resched() which can actually reschedule. >> The splat in the commit message confirms preempt_count is 0 while RCU nest >> depth is 1. With preempt_count==0, should_resched(0) can be true and >> __cond_resched() will call preempt_schedule_common() for a real reschedule. >> >> Additionally, in configurations with CONFIG_PREEMPT_RCU=n where >> rcu_read_lock() is preempt_disable(), __cond_resched() falls through to >> rcu_all_qs() which calls rcu_qs() to report a quiescent state from inside >> an RCU read-side critical section. That's a correctness problem beyond just >> the debug check. >> >> So the call can either reschedule (PREEMPT_DYNAMIC none/voluntary) or report >> a bogus quiescent state (non-preemptible RCU). Could the justification be >> reworded to explain that the loop runs inside the iterator's RCU read-side >> critical section and must not reschedule or report a quiescent state there? >> The code change itself is correct and matches the existing pattern in >> tcp_abort() and udp_abort(). > or maybe simply remove cond_resched(), hoping 7dadeaa6e851 would > resolve the scheduling issue. > Good suggestion. cond_resched has become old practice under CONFIG_PREEMPT_LAZY