On Sun, Sep 6, 2026 at 1:23 AM <[email protected]> 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: > > <TASK> > > 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 > > </TASK> > > > > 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 <[email protected]> > > 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. > > > --- > AI reviewed your patch. Please fix the bug or email reply why it's not a bug. > See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md > > CI run summary: https://github.com/kernel-patches/bpf/actions/runs/34020353095
