Date:	Thu, 29 Mar 2007 18:18:36 +0530
From:	Maneesh Soni <maneesh@...ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	Andreas Mohr <andi@...x01.fht-esslingen.de>,
	Greg KH <greg@...ah.com>, linux-kernel@...r.kernel.org,
	Dipankar Sarma <dipankar@...ibm.com>, ego@...ibm.com
Subject: Re: tty OOPS (Re: 2.6.21-rc5-mm2)

On Wed, Mar 28, 2007 at 01:07:56PM -0700, Andrew Morton wrote:
> On Wed, 28 Mar 2007 22:56:32 +0400
> Alexey Dobriyan <adobriyan@...il.com> wrote:
> 
> > On Wed, Mar 28, 2007 at 10:38:14PM +0400, Alexey Dobriyan wrote:
> > > On Wed, Mar 28, 2007 at 08:04:46PM +0200, Andreas Mohr wrote:
> > > > [unrelated maintainers removed, Alexey added]
> > > >
> > > > On Wed, Mar 28, 2007 at 07:45:24PM +0200, Andreas Mohr wrote:
> > > > > Hi,
> > > > >
> > > > > just wanted to add that when analyzing the backtrace I found the comment
> > > > > at drivers/char/vt.c/con_close() to be VERY suspicious...
> > > > > (need to take tty_mutex to prevent concurrent thread tty access).
> > > > > This might just be what happened here despite trying to protect against it.
> > > >
> > > > OK, can we assume that one of
> > > >
> > > > +protect-tty-drivers-list-with-tty_mutex.patch
> > > > +tty-minor-merge-correction.patch
> > > > +tty-in-tiocsctty-when-we-steal-a-tty-hang-it-up-fix.patch
> > > >
> > > > is responsible / not implemented fully?
> > >
> > > #2 is just comment removal.
> > >
> > > I may state the obvious, but __iget() in sysfs_drop_dentry() gets NULL
> > > inode and you aren't failing on spin_lock one line above because of UP
> > > without spinlock debugging.
> > 
> > The only suspicious new patch in -rc5-mm1 to me is
> > fix-sysfs-reclaim-crash.patch which removes "sd->s_dentry = NULL;". Note
> > that whole sysfs_drop_dentry() is NOP if ->s_dentry is NULL.
> > 
> > Could you try to revert it?
> > 
> > 	Alexey, who knows very little about sysfs internals
> 
> cc's added.
> 
> 
> Also added is the sad little missive I sent to the USB guys last night,
> which is similar-looking:
> 
> 
> 
> Begin forwarded message:
> 
> Date: Wed, 28 Mar 2007 00:34:45 -0700
> From: Andrew Morton <akpm@...ux-foundation.org>
> To: linux-usb-devel@...ts.sourceforge.net
> Subject: usb/sysfs oops in 2.6.21-rc5-mm1
> 
> 
> 
> I think the connector wasn't pushed in terribly well, so there might have
> been some contact bounce.
> 
> 
> [15813.836000] ipw2200: Firmware error detected.  Restarting.
> [17200.268000] hub 2-0:1.0: port 1 disabled by hub (EMI?), re-enabling...
> [17200.268000] usb 2-1: USB disconnect, address 4
> [17200.268000] BUG: unable to handle kernel NULL pointer dereference at virtual address 00000024
> [17200.268000]  printing eip:
> [17200.268000] c016e447
> [17200.268000] *pde = 00000000
> [17200.268000] Oops: 0000 [#1]
> [17200.268000] last sysfs file: block/sr0/size
> [17200.268000] Modules linked in: udf i915 drm ipw2200 sonypi ipv6 autofs4 hidp l2cap sunrpc nf_conntrack_netbios_ns ipt_REJECT nf_conntrack_ipv4 xt_state nf_conntrack nfnetlink xt_tcpudp iptable_filter ip_tables x_tables cpufreq_ondemand video sbs button battery asus_acpi ac nvram hci_usb bluetooth ieee80211 ohci1394 ieee1394 joydev ieee80211_crypt snd_hda_intel snd_hda_codec ehci_hcd uhci_hcd sg snd_seq_dummy snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device snd_pcm_oss snd_mixer_oss snd_pcm snd_timer snd sr_mod cdrom piix soundcore i2c_i801 snd_page_alloc i2c_core pcspkr generic ext3 jbd ide_disk ide_core
> [17200.268000] CPU:    0
> [17200.268000] EIP:    0060:[<c016e447>]    Not tainted VLI
> [17200.268000] EFLAGS: 00010246   (2.6.21-rc5-mm1 #1)
> [17200.268000] EIP is at __iget+0x3/0x48
> [17200.268000] eax: 00000000   ebx: 00000000   ecx: 00000000   edx: c8a90514
> [17200.268000] esi: c8a90514   edi: 00000000   ebp: c8cea5e4   esp: c210fe5c
> [17200.268000] ds: 007b   es: 007b   fs: 00d8  gs: 0000  ss: 0068
> [17200.268000] Process khubd (pid: 155, ti=c210e000 task=c209b6f0 task.ti=c210e000)
> [17200.268000] Stack: c2493a14 c0192933 c8cea5e8 c0338373 c0338373 c8cea5e4 c0192a90 c889ba24 
> [17200.268000]        c033836f c8a90514 c8cea58c c889ba08 c8556a40 df8918c0 c24e6418 c0230d46 
> [17200.268000]        c889ba08 c889ba08 c0230dd8 c889ba08 c889ba00 df8918c0 c24e6418 c0230ffa 
> [17200.268000] Call Trace:
> [17200.268000]  [<c0192933>] sysfs_drop_dentry+0x2b/0xc3
> [17200.268000]  [<c0192a90>] sysfs_hash_and_remove+0x86/0x12c
> [17200.268000]  [<c0230d46>] device_remove_file+0x19/0x25
> [17200.268000]  [<c0230dd8>] device_del+0x26/0x240
> [17200.268000]  [<c0230ffa>] device_unregister+0x8/0x10
> [17200.268000]  [<c026739a>] usb_remove_ep_files+0x4d/0x60
> [17200.268000]  [<c0260031>] usb_new_device+0x199/0x1ab
> [17200.268000]  [<c0266d14>] usb_remove_sysfs_intf_files+0x1e/0x43
> [17200.268000]  [<c026312d>] usb_disable_device+0x55/0xbb
> [17200.268000]  [<c0260415>] usb_disconnect+0x87/0x100
> [17200.268000]  [<c0260842>] hub_thread+0x361/0xa70
> [17200.268000]  [<c016d394>] d_lookup+0x16/0x31
> [17200.268000]  [<c01174df>] __wake_up_common+0x31/0x4f
> [17200.268000]  [<c0128754>] autoremove_wake_function+0x0/0x35
> [17200.268000]  [<c02604e1>] hub_thread+0x0/0xa70
> [17200.268000]  [<c01285f7>] kthread+0xa0/0xc9
> [17200.268000]  [<c0128557>] kthread+0x0/0xc9
> [17200.268000]  [<c010464f>] kernel_thread_helper+0x7/0x10
> [17200.268000]  =======================
> [17200.268000] Code: 00 00 00 89 d8 81 ce 00 02 00 00 e8 3e ba 01 00 8b 43 20 31 c9 89 f2 89 04 24 89 d8 e8 19 25 01 00 58 5b 5e c3 90 90 90 53 89 c3 <83> 78 24 00 74 05 ff 40 24 eb 38 ff 40 24 f6 80 2c 01 00 00 0f 
> [17200.268000] EIP: [<c016e447>] __iget+0x3/0x48 SS:ESP 0068:c210fe5c
> [17327.844000] ipw2200: Firmware error detected.  Restarting.

This is indeed because of my patch in -mm1. Gautham has also got this 
recreated in his CPU hotplug testing and he has thankfully provided me
a crashdump.

In the dump, so far it looks like that we have a sysfs_dirent (corresponding to
file /sys/devices/system/cpu/cpu1/microcode/processor_flags), with a corrupted
s_dentry.

crash> struct sysfs_dirent c7721f2c
struct sysfs_dirent {
  s_count = {
    counter = 1
  },
  s_sibling = {
    next = 0xc7721f30,
    prev = 0xc7721f30
  },
  s_children = {
    next = 0xc7721f38,
    prev = 0xc7721f38
  },
  s_element = 0xc05ec7a4,
  s_type = 4,
  s_mode = 33024,
  s_dentry = 0xc790d254,
  s_iattr = 0x0,
  s_event = {
    counter = 1
  }
}

crash> struct dentry.d_count 0xc790d254
  d_count = {
    counter = 0
  },

crash> struct dentry.d_flags 0xc790d254
  d_flags = 0,

I am still looking at this problem and will update further.

Thanks
Maneesh


--
Maneesh Soni
Linux Technology Center,
IBM India Systems and Technology Lab, 
Bangalore, India
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