On Mon, 26 Jan 2026 18:11:45 -0500 Steven Rostedt <[email protected]> wrote:
> The current use of guard(preempt_notrace)() within __DECLARE_TRACE() > to protect invocation of __DO_TRACE_CALL() means that BPF programs > attached to tracepoints are non-preemptible. This is unhelpful in > real-time systems, whose users apparently wish to use BPF while also > achieving low latencies. > > Change the protection of tracepoints to use fast_srcu() instead. > This will allow the callbacks to be able to be preempted. This also > means that the callbacks themselves need to be able to handle this > new found preemption ability. > > For perf, add a guard(preempt) inside its handler too keep the old behavior > of perf events being called with preemption disabled. > > For BPF, add a migrate_disable() to its handler. Actually, just replace > the rcu_read_lock() with rcu_read_lock_dont_migrate() and make it > cover more of the BPF callback handler. My tests just triggered this, so I'm removing them from my queue for now. -- Steve [ 204.194772] ------------[ cut here ]------------ [ 204.194789] WARNING: kernel/rcu/srcutree.c:792 at __srcu_check_read_flavor+0x5c/0xb0, CPU#1: swapper/1/0 [ 204.194800] Modules linked in: [ 204.194817] CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Not tainted 6.19.0-rc7-test-00018-g2c774d6ad074-dirty #32 PREEMPT(voluntary) [ 204.194821] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.17.0-debian-1.17.0-1 04/01/2014 [ 204.194824] RIP: 0010:__srcu_check_read_flavor+0x5c/0xb0 [ 204.194829] Code: 84 c9 74 19 39 f1 74 45 0f 0b 85 c0 74 2e 39 c1 74 45 0f 0b 39 f0 75 3f c3 cc cc cc cc 85 c0 74 16 83 fe 04 75 ee 0f 0b eb ea <0f> 0b 8d 46 ff 85 f0 74 ba 0f 0b eb b6 83 fe 04 74 3a 31 c0 f0 0f [ 204.194832] RSP: 0018:fffffe4c48325b50 EFLAGS: 00010002 [ 204.194835] RAX: 0000000000000001 RBX: ffffffff8791e5a0 RCX: 0000000000000000 [ 204.194836] RDX: 00000000ffffffff RSI: 0000000000000004 RDI: ffffffff879f1180 [ 204.194838] RBP: ffff8e6453fd2000 R08: 0000000000000001 R09: 0000000000000000 [ 204.194839] R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000001 [ 204.194840] R13: fffffe4c48325ef8 R14: ffffffff85eeae93 R15: ffff8e6453906900 [ 204.194842] FS: 0000000000000000(0000) GS:ffff8e6533593000(0000) knlGS:0000000000000000 [ 204.194844] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 204.194845] CR2: 000055d1e7cf8cc0 CR3: 000000010b0cc004 CR4: 0000000000172ef0 [ 204.194850] Call Trace: [ 204.194866] <NMI> [ 204.194868] lock_release+0x215/0x320 [ 204.194886] ? arch_perf_update_userpage+0x6c/0xf0 [ 204.195214] perf_event_update_userpage+0x158/0x2e0 [ 204.195538] x86_perf_event_set_period+0xc1/0x180 [ 204.195811] handle_pmi_common+0x1ac/0x450 [ 204.198605] ? __get_next_timer_interrupt+0x185/0x370 [ 204.198914] intel_pmu_handle_irq+0x10e/0x510 [ 204.199032] ? nmi_handle.part.0+0x30/0x270 [ 204.199197] ? __get_next_timer_interrupt+0x185/0x370 [ 204.199404] perf_event_nmi_handler+0x34/0x60 [ 204.199523] nmi_handle.part.0+0xc9/0x270
