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Subjectdebugfs related oops in mac80211/ath9k

I got the oops attached below while running 2 threads:
cat /sys/kernel/debug/ieee80211/phy*/*
while :; do echo '0000:02:00.0' > unbind ; echo '0000:02:00.0' > bind; done
note that the oops is from suse kernel-of-the-day kernel. Happens with
vanilla 2.6.30 too.

sc->ah is NULL in ath9k_hw_gettsf64. Not good. file->private_data points
to freed memory (which is allocated by the same buddy a bit later in
this case). I got also another oopses in mac80211 layer, like in
frequency_read function. It has the same root cause.

The reading process still holds a reference to the node, so it's not
deleted. fops->read is called from vfs_read, but memory pointed by
file->private_data might be freed already.

We need some kind of barrier in debugfs_remove, so that all processes
with that file opened finishes first. Any ideas?

BUG: unable to handle kernel NULL pointer dereference at 0000000000000068
IP: [<ffffffffa08704a0>] ath9k_ioread32+0x22/0x94 [ath9k]
PGD 8df2067 PUD 7dd28067 PMD 0
Oops: 0000 [#3] SMP
last sysfs file: /sys/bus/pci/drivers/ath9k/bind
Modules linked in: ath9k snd_seq_dummy btusb cryptd aes_x86_64
aes_generic cpufreq_stats tun radeon drm nfs lockd fscache(N) nfs_acl
auth_rpcgss sunrpc af_packet bridge stp llc(N) bnep sco rfcomm l2cap
bluetooth snd_pcm_oss snd_mixer_oss snd_seq ipv6 snd_seq_device
cpufreq_conservative cpufreq_userspace cpufreq_powersave acpi_cpufreq
fuse loop snd_hda_codec_si3054(N) snd_hda_codec_realtek(N) arc4 ecb
snd_hda_intel snd_hda_codec(N) snd_hwdep snd_pcm mac80211 snd_timer
rfkill iTCO_wdt stkwebcam snd iTCO_vendor_support processor video
thermal videodev soundcore tpm_infineon i2c_i801 cfg80211 thermal_sys
v4l1_compat sr_mod asus_laptop kvm_intel tpm r8169 snd_page_alloc
intel_agp pcspkr i2c_core button battery ac output serio_raw cdrom
v4l2_compat_ioctl32(N) hwmon joydev tpm_bios led_class kvm sg uinput
usbhid hid uhci_hcd ata_piix ehci_hcd dm_mod [last unloaded: ath9k]
Supported: Yes
Pid: 25328, comm: cat Tainted: G D N
2.6.30-master_20090610141226_1b1ebc88-default #1 F2JE
RIP: 0010:[<ffffffffa08704a0>] [<ffffffffa08704a0>]
ath9k_ioread32+0x22/0x94 [ath9k]
RSP: 0018:ffff880074687d88 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff880074687f50
RDX: ffffffffa0884016 RSI: 0000000000008050 RDI: 0000000000000000
RBP: ffff880074687dc8 R08: ffffffffa0261769 R09: 00007f5be6f09665
R10: 0000000000001fff R11: 0000000000000246 R12: 0000000000008050
R13: 0000000000001000 R14: 000000000060d000 R15: 0000000000000000
FS: 00007f5be6ed76f0(0000) GS:ffff88000104c000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 0000000000000068 CR3: 000000001339c000 CR4: 00000000000026e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process cat (pid: 25328, threadinfo ffff880074686000, task ffff88005a0fa680)
ffff880076c96cb8 ffffffff809221f8 ffff880074687dd8 0000000012d27d63
ffff880074687dd8 0000000000000000 ffff88003fb71100 0000000000001000
ffff880074687df8 ffffffffa0870539 ffffffff802449b7 0000000012d27d63
Call Trace:
[<ffffffffa0870539>] ath9k_hw_gettsf64+0x27/0x5b [ath9k]
[<ffffffffa0884054>] ath9k_get_tsf+0x3e/0x6b [ath9k]
[<ffffffffa02617ab>] tsf_read+0x42/0x9b [mac80211]
[<ffffffff80303f18>] vfs_read+0xb5/0x126
[<ffffffff80304071>] sys_read+0x54/0x8c
[<ffffffff8020c142>] system_call_fastpath+0x16/0x1b
[<00007f5be6a617c0>] 0x7f5be6a617c0
Code: 74 05 e8 51 4b 9e df c9 c3 55 48 89 e5 41 55 41 54 41 89 f4 53 48
89 fb 48 83 ec 28 65 48 8b 04 25 28 00 00 00 48 89 45 d8 31 c0 <83> 7f
68 01 48 8b 3f 75 3b 48 81 c7 58 01 00 00 e8 7a c3 d7 df
RIP [<ffffffffa08704a0>] ath9k_ioread32+0x22/0x94 [ath9k]
RSP <ffff880074687d88>
CR2: 0000000000000068
---[ end trace b782e2e515247664 ]---

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