On 4 August 2016 at 17:17, Vegard Nossum <[email protected]> wrote: > On 4 August 2016 at 14:37, Peter Zijlstra <[email protected]> wrote: >> On Fri, Jul 29, 2016 at 11:41:11PM +0200, Vegard Nossum wrote: >> >>> Digging a bit deeper into this, it seems the event itself is getting >>> created by perf_event_open() and it gets added to the pmu_event_list >>> through: >>> >>> perf_event_open() >>> - perf_event_alloc() >>> - account_event() >>> - account_pmu_sb_event() >>> - attach_sb_event() >>> > [...] >>> So I guess the question is... should the event be attached (= put on >>> the list) before ->ctx gets set? Or should the cgroup code check for a >>> NULL ->ctx? >> >> Does this fix it? Ordering is a bit of a mess, adding the events to the >> list _after_ they've been installed has the risk of missing things I >> think, nor does that result in particularly nice code. >> >> Then again, this isn't pretty either. > > Patch seems to fix it here, thanks! Feel free to add: > > Tested-by: Vegard Nossum <[email protected]>
BTW, this seems to show up slightly more frequently although I've seen it a couple of times before without your patch too so it's probably unrelated: WARNING: CPU: 0 PID: 1244 at arch/x86/kernel/hw_breakpoint.c:121 arch_install_hw_breakpoint+0x284/0x2f0 Can't find any breakpoint slot CPU: 0 PID: 1244 Comm: trinity-c0 Not tainted 4.7.0+ #73 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.9.3-0-ge2fc41e-prebuilt.qemu-project.org 04/01/20 14 ffffffff83a1a5a0 ffff880116b6f860 ffffffff81d75571 ffff880116b6f8d8 0000000000000000 ffff880116b6f8a8 ffffffff810fd28f ffff880115fb5a00 ffff880100000079 ffffed0022d6df17 0000000000000004 ffff88010e202a80 Call Trace: [<ffffffff81d75571>] dump_stack+0x65/0x84 [<ffffffff810fd28f>] __warn+0x17f/0x1a0 [<ffffffff810fd342>] warn_slowpath_fmt+0x92/0xb0 [<ffffffff810fd2b0>] ? __warn+0x1a0/0x1a0 [<ffffffff8135b5ba>] ? perf_event_update_userpage+0x3ca/0x660 [<ffffffff81064144>] arch_install_hw_breakpoint+0x284/0x2f0 [<ffffffff81371e44>] hw_breakpoint_add+0xd4/0x100 [<ffffffff81354d37>] event_sched_in.isra.100+0x3a7/0xa40 [<ffffffff813554d3>] group_sched_in+0x103/0x3e0 [<ffffffff81066579>] ? sched_clock+0x9/0x10 [<ffffffff81355fbd>] ctx_sched_in+0x80d/0x16f0 [<ffffffff81356f00>] perf_event_sched_in+0x60/0x80 [<ffffffff81356f80>] ctx_resched+0x60/0xa0 [<ffffffff81357d67>] __perf_install_in_context+0x247/0x320 [<ffffffff81357b20>] ? __perf_event_enable+0xb60/0xb60 [<ffffffff81347fa0>] ? perf_duration_warn+0x40/0x40 [<ffffffff813480b5>] remote_function+0x115/0x1a0 [<ffffffff81347fa0>] ? perf_duration_warn+0x40/0x40 [<ffffffff8125d801>] generic_exec_single+0x191/0x290 [<ffffffff81347fa0>] ? perf_duration_warn+0x40/0x40 [<ffffffff8125db2e>] smp_call_function_single+0xde/0x350 [<ffffffff8125da50>] ? generic_smp_call_function_single_interrupt+0x10/0x10 [<ffffffff81341f80>] perf_install_in_context+0x200/0x370 [<ffffffff81341d80>] ? perf_remove_from_context+0xc0/0xc0 [<ffffffff81357b20>] ? __perf_event_enable+0xb60/0xb60 [<ffffffff81361482>] SYSC_perf_event_open+0xd62/0x1cf0 [<ffffffff81360720>] ? perf_event_set_output+0x400/0x400 [<ffffffff81dd4603>] ? __this_cpu_preempt_check+0x13/0x20 [<ffffffff81369e80>] ? perf_pmu_unregister+0x470/0x470 [<ffffffff81369e89>] SyS_perf_event_open+0x9/0x10 [<ffffffff81005391>] do_syscall_64+0x1a1/0x460 [<ffffffff813742fa>] ? __context_tracking_enter+0xaa/0x200 [<ffffffff8389746a>] entry_SYSCALL64_slow_path+0x25/0x25 ---[ end trace 966c767fd836202d ]--- Vegard
