perf: WARNING: kernel/events/core.c:4893 perf_mmap_close

[Vince Weaver]

Hello

running the perf_fuzzer on Haswell, this is a new warning I don't think 
I've seen before.

It works out to be this code here:

                /* this has to be the last one */
                rb_free_aux(rb);
                WARN_ON_ONCE(atomic_read(&rb->aux_refcount));

                mutex_unlock(&event->mmap_mutex);

[ 1102.250898] ------------[ cut here ]------------
[ 1102.257316] WARNING: CPU: 5 PID: 26043 at kernel/events/core.c:4893 perf_mmap_close+0x389/0x390
[ 1102.269074] Modules linked in: binfmt_misc intel_rapl iosf_mbi x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel kvm irqbypass crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel snd_hda_codec_hdmi aes_x86_64 lrw gf128mul glue_helper snd_hda_codec_realtek snd_hda_codec_generic ablk_helper ppdev iTCO_wdt snd_hda_intel snd_hda_codec snd_hda_core cryptd evdev iTCO_vendor_support snd_hwdep snd_pcm snd_timer snd i915 drm_kms_helper parport_pc wmi parport psmouse tpm_tis tpm_tis_core pcspkr serio_raw sg button i2c_i801 soundcore lpc_ich drm mei_me mfd_core i2c_smbus tpm mei video battery i2c_algo_bit sr_mod sd_mod cdrom ahci libahci xhci_pci libata ehci_pci xhci_hcd ehci_hcd e1000e usbcore ptp crc32c_intel scsi_mod pps_core usb_common fan thermal
[ 1102.367852] CPU: 5 PID: 26043 Comm: perf_fuzzer Not tainted 4.8.0-rc1+ #187
[ 1102.377206] Hardware name: LENOVO 10AM000AUS/SHARKBAY, BIOS FBKT72AUS 01/26/2014
[ 1102.387192]  0000000000000000 ffff880117b2bdd8 ffffffff81437641 0000000000000000
[ 1102.397466]  0000000000000000 ffff880117b2be18 ffffffff81076bab 0000131d00000282
[ 1102.407748]  ffff880118211c00 ffff8801173502d8 ffff880117350000 ffff880117d20458
[ 1102.418074] Call Trace:
[ 1102.421424]  [<ffffffff81437641>] dump_stack+0x63/0x82
[ 1102.428393]  [<ffffffff81076bab>] __warn+0xcb/0xf0
[ 1102.434873]  [<ffffffff81076c9d>] warn_slowpath_null+0x1d/0x20
[ 1102.442797]  [<ffffffff81174ab9>] perf_mmap_close+0x389/0x390
[ 1102.450557]  [<ffffffff81174955>] ? perf_mmap_close+0x225/0x390
[ 1102.458569]  [<ffffffff8116cf90>] ? perf_iterate_ctx+0x160/0x160
[ 1102.466720]  [<ffffffff811c0ca2>] remove_vma+0x32/0x70
[ 1102.473658]  [<ffffffff811c2cc8>] do_munmap+0x2b8/0x460
[ 1102.480721]  [<ffffffff811c2f33>] SyS_munmap+0x53/0x70
[ 1102.487663]  [<ffffffff817221b6>] entry_SYSCALL_64_fastpath+0x1e/0xad
[ 1102.496649] ---[ end trace 7ff7a520eaea4ee0 ]---