Re: 2.6.31-rc tty layer instabilities

Alan Cox writes:
With 2.6.31-rc1 I saw warnings like the following:

Somehow you got a closed ldisc being closed again which means the hangup
raced some other event.

With 2.6.31-rc2 I instead see oopses:

I put in a NULL assignment to force any offenders to explode.

We've executed tty_ldisc_release on the port meaning we already took the
path through tty_release_dev() which is called when the final close() of
the tty occurs.

After this we've come via disassociate_ctty into a hangup (caused by us
being the controlling tty owner who exits).

Jul 6 15:23:49 brewer kernel: [<c0232c1c>] ? tty_ldisc_hangup+0xdc/0x1d0
Jul 6 15:23:49 brewer kernel: [<c022bbb5>] ? do_tty_hangup+0xc5/0x340
Jul 6 15:23:49 brewer kernel: [<c022c19f>] ? disassociate_ctty+0x3f/0x1d0

At this point we hold a kref to the tty still but the tty->ldisc is dead

In the normal case we would be fine as we kill off any pending hangup
processing in the close down. In this case we are not because the hangup
process was initiated after the last close

This happens perhaps once every 5 or so reboots. I haven't yet seen
any specific usage pattern that might be the trigger.

I suspect its simply a matter of timing randomness.

Does this help:

tty: defer ldisc kill

Unfortunately this made things worse. Now I get loads of warnings during
bootup before the login prompt is shown:

Adding 2008116k swap on /dev/sda2. Priority:-1 extents:1 across:2008116k
------------[ cut here ]------------
WARNING: at drivers/char/tty_ldisc.c:210 tty_ldisc_put+0x81/0x90()
Hardware name: System Product Name
Modules linked in: snd_hda_intel snd_hda_codec snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device snd_pcm_oss snd_mixer_oss sg snd_pcm sr_mod cdrom 8139too snd_timer mii bitrev crc32 snd soundcore snd_page_alloc floppy ehci_hcd uhci_hcd usbcore
Pid: 1387, comm: init Not tainted 2.6.31-rc2 #1
Call Trace:
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff81037e74>] ? warn_slowpath_common+0x74/0xd0
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff81164e20>] ? tty_ldisc_hangup+0x130/0x210
[<ffffffff8115d1ee>] ? do_tty_hangup+0xde/0x3d0
[<ffffffff81090afa>] ? filp_close+0x4a/0x80
[<ffffffff8115d87b>] ? disassociate_ctty+0x4b/0x230
[<ffffffff8103b80a>] ? do_exit+0x69a/0x6f0
[<ffffffff8103b899>] ? do_group_exit+0x39/0xa0
[<ffffffff8103b912>] ? sys_exit_group+0x12/0x20
[<ffffffff8100b3ab>] ? system_call_fastpath+0x16/0x1b
---[ end trace 2068c4982373eafa ]---
tty_ldisc_deref: no references.
NET: Registered protocol family 17
eth0: link up, 100Mbps, full-duplex, lpa 0x45E1
RPC: Registered udp transport module.
RPC: Registered tcp transport module.
warning: `dbus-daemon' uses 32-bit capabilities (legacy support in use)
------------[ cut here ]------------
WARNING: at drivers/char/tty_ldisc.c:210 tty_ldisc_put+0x81/0x90()
Hardware name: System Product Name
Modules linked in: sunrpc af_packet snd_hda_intel snd_hda_codec snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device snd_pcm_oss snd_mixer_oss sg snd_pcm sr_mod cdrom 8139too snd_timer mii bitrev crc32 snd soundcore snd_page_alloc floppy ehci_hcd uhci_hcd usbcore
Pid: 1996, comm: mingetty Tainted: G W 2.6.31-rc2 #1
Call Trace:
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff81037e74>] ? warn_slowpath_common+0x74/0xd0
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff81164e20>] ? tty_ldisc_hangup+0x130/0x210
[<ffffffff8115d1ee>] ? do_tty_hangup+0xde/0x3d0
[<ffffffff8115d50a>] ? tty_vhangup_self+0x1a/0x30
[<ffffffff810909be>] ? sys_vhangup+0x1e/0x30
[<ffffffff8100b3ab>] ? system_call_fastpath+0x16/0x1b
---[ end trace 2068c4982373eafb ]---
tty_ldisc_deref: no references.
------------[ cut here ]------------
WARNING: at drivers/char/tty_ldisc.c:210 tty_ldisc_put+0x81/0x90()
Hardware name: System Product Name
Modules linked in: sunrpc af_packet snd_hda_intel snd_hda_codec snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device snd_pcm_oss snd_mixer_oss sg snd_pcm sr_mod cdrom 8139too snd_timer mii bitrev crc32 snd soundcore snd_page_alloc floppy ehci_hcd uhci_hcd usbcore
Pid: 1993, comm: mingetty Tainted: G W 2.6.31-rc2 #1
Call Trace:
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff81037e74>] ? warn_slowpath_common+0x74/0xd0
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff81164e20>] ? tty_ldisc_hangup+0x130/0x210
[<ffffffff8115d1ee>] ? do_tty_hangup+0xde/0x3d0
[<ffffffff8115d50a>] ? tty_vhangup_self+0x1a/0x30
[<ffffffff810909be>] ? sys_vhangup+0x1e/0x30
[<ffffffff8100b3ab>] ? system_call_fastpath+0x16/0x1b
---[ end trace 2068c4982373eafc ]---
tty_ldisc_deref: no references.
------------[ cut here ]------------
WARNING: at drivers/char/tty_ldisc.c:210 tty_ldisc_put+0x81/0x90()
Hardware name: System Product Name
Modules linked in: sunrpc af_packet snd_hda_intel snd_hda_codec snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device snd_pcm_oss snd_mixer_oss sg snd_pcm sr_mod cdrom 8139too snd_timer mii bitrev crc32 snd soundcore snd_page_alloc floppy ehci_hcd uhci_hcd usbcore
Pid: 1994, comm: mingetty Tainted: G W 2.6.31-rc2 #1
Call Trace:
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff81037e74>] ? warn_slowpath_common+0x74/0xd0
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff81164e20>] ? tty_ldisc_hangup+0x130/0x210
[<ffffffff8115d1ee>] ? do_tty_hangup+0xde/0x3d0
[<ffffffff8115d50a>] ? tty_vhangup_self+0x1a/0x30
[<ffffffff810909be>] ? sys_vhangup+0x1e/0x30
[<ffffffff8100b3ab>] ? system_call_fastpath+0x16/0x1b
---[ end trace 2068c4982373eafd ]---
tty_ldisc_deref: no references.
------------[ cut here ]------------
WARNING: at drivers/char/tty_ldisc.c:210 tty_ldisc_put+0x81/0x90()
Hardware name: System Product Name
Modules linked in: sunrpc af_packet snd_hda_intel snd_hda_codec snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device snd_pcm_oss snd_mixer_oss sg snd_pcm sr_mod cdrom 8139too snd_timer mii bitrev crc32 snd soundcore snd_page_alloc floppy ehci_hcd uhci_hcd usbcore
Pid: 1992, comm: mingetty Tainted: G W 2.6.31-rc2 #1
Call Trace:
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff81037e74>] ? warn_slowpath_common+0x74/0xd0
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff81164e20>] ? tty_ldisc_hangup+0x130/0x210
[<ffffffff8115d1ee>] ? do_tty_hangup+0xde/0x3d0
[<ffffffff8115d50a>] ? tty_vhangup_self+0x1a/0x30
[<ffffffff810909be>] ? sys_vhangup+0x1e/0x30
[<ffffffff8100b3ab>] ? system_call_fastpath+0x16/0x1b
---[ end trace 2068c4982373eafe ]---
tty_ldisc_deref: no references.
------------[ cut here ]------------
WARNING: at drivers/char/tty_ldisc.c:210 tty_ldisc_put+0x81/0x90()
Hardware name: System Product Name
Modules linked in: sunrpc af_packet snd_hda_intel snd_hda_codec snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device snd_pcm_oss snd_mixer_oss sg snd_pcm sr_mod cdrom 8139too snd_timer mii bitrev crc32 snd soundcore snd_page_alloc floppy ehci_hcd uhci_hcd usbcore
Pid: 1995, comm: mingetty Tainted: G W 2.6.31-rc2 #1
Call Trace:
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff81037e74>] ? warn_slowpath_common+0x74/0xd0
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff81164e20>] ? tty_ldisc_hangup+0x130/0x210
[<ffffffff8115d1ee>] ? do_tty_hangup+0xde/0x3d0
[<ffffffff8115d50a>] ? tty_vhangup_self+0x1a/0x30
[<ffffffff810909be>] ? sys_vhangup+0x1e/0x30
[<ffffffff8100b3ab>] ? system_call_fastpath+0x16/0x1b
---[ end trace 2068c4982373eaff ]---
tty_ldisc_deref: no references.
------------[ cut here ]------------
WARNING: at drivers/char/tty_ldisc.c:210 tty_ldisc_put+0x81/0x90()
Hardware name: System Product Name
Modules linked in: sunrpc af_packet snd_hda_intel snd_hda_codec snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device snd_pcm_oss snd_mixer_oss sg snd_pcm sr_mod cdrom 8139too snd_timer mii bitrev crc32 snd soundcore snd_page_alloc floppy ehci_hcd uhci_hcd usbcore
Pid: 1997, comm: mingetty Tainted: G W 2.6.31-rc2 #1
Call Trace:
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff81037e74>] ? warn_slowpath_common+0x74/0xd0
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff81164e20>] ? tty_ldisc_hangup+0x130/0x210
[<ffffffff8115d1ee>] ? do_tty_hangup+0xde/0x3d0
[<ffffffff8115d50a>] ? tty_vhangup_self+0x1a/0x30
[<ffffffff810909be>] ? sys_vhangup+0x1e/0x30
[<ffffffff8100b3ab>] ? system_call_fastpath+0x16/0x1b
---[ end trace 2068c4982373eb00 ]---
tty_ldisc_deref: no references.
------------[ cut here ]------------
WARNING: at drivers/char/tty_ldisc.c:210 tty_ldisc_put+0x81/0x90()
Hardware name: System Product Name
Modules linked in: sunrpc af_packet snd_hda_intel snd_hda_codec snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device snd_pcm_oss snd_mixer_oss sg snd_pcm sr_mod cdrom 8139too snd_timer mii bitrev crc32 snd soundcore snd_page_alloc floppy ehci_hcd uhci_hcd usbcore
Pid: 1992, comm: login Tainted: G W 2.6.31-rc2 #1
Call Trace:
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff81037e74>] ? warn_slowpath_common+0x74/0xd0
[<ffffffff811642f1>] ? tty_ldisc_put+0x81/0x90
[<ffffffff81164e20>] ? tty_ldisc_hangup+0x130/0x210
[<ffffffff8115d1ee>] ? do_tty_hangup+0xde/0x3d0
[<ffffffff8115d50a>] ? tty_vhangup_self+0x1a/0x30
[<ffffffff810909be>] ? sys_vhangup+0x1e/0x30
[<ffffffff8100b3ab>] ? system_call_fastpath+0x16/0x1b
---[ end trace 2068c4982373eb01 ]---
tty_ldisc_deref: no references.
[drm] Initialized drm 1.1.0 20060810
pci 0000:01:00.0: PCI INT A -> GSI 16 (level, low) -> IRQ 16
pci 0000:01:00.0: setting latency timer to 64
[drm] Initialized radeon 1.30.0 20080528 for 0000:01:00.0 on minor 0
mtrr: type mismatch for c0000000,10000000 old: write-back new: write-combining
mtrr: type mismatch for c0000000,10000000 old: write-back new: write-combining
mtrr: type mismatch for c0000000,10000000 old: write-back new: write-combining
mtrr: type mismatch for c0000000,10000000 old: write-back new: write-combining
mtrr: type mismatch for c0000000,10000000 old: write-back new: write-combining
[drm] Setting GART location based on new memory map
[drm] Loading R300 Microcode
[drm] Num pipes: 1
[drm] writeback test succeeded in 1 usecs

/Mikael
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