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SubjectRe: 2.6 must-fix list, v3

The full list:

Must-fix bugs


- TTY locking is broken.

- see FIXME in do_tty_hangup(). This causes ppp BUGs in local_bh_enable()

- Other problems: aviro, dipankar, Alan have details.

- somebody will have to document the tty driver and ldisc API


- rmk: I think we need a generic RTC driver (which is backed by real RTCs).
Integrator-based stuff has a 32-bit 1Hz counter RTC with alarm, as has the
SA11xx, and probably PXA. There's another implementation for the RiscPC
and ARM26 stuff. I'd rather not see 4 implementations of the RTC userspace
API, but one common implementation so that stuff gets done in a consistent

We postponed this at the beginning of 2.4 until 2.5 happened. We're now
at 2.5, and I'm about to add at least one more (the Integrator
implementation.) This isn't sane imo.


- RAID0 dies on strangely aligned BIOs

- Need to hoist BIO-split code out of device mapper, use that.


1/ RAID5 should work fine. It accepts any sort of bio and always
submits a 1-page bio to the underlying device, and if my
understanding is correct, every device must be able to handle a
single page bio, no matter what the alignment (which is why raid0
has a problem - it doesn't).

2/ RAID1 works pretty well. The only improvement needed is to define
a merge_bvec_fn function which passes the question down to lower
layers. This should be easy except for the small fact that it is
impossible :-) There is no enforced pairing between calls to
merge_bvec_fn and submit_bh, so it is possible that a hot spare
with different restrictions could get swapped in between the one
and the other and could confuse things. I suspect that can be
worked around somehow though...

Someone sent me a patch that is sorely needed - it allows you
to simply call blk_queue_stack() (or somethink like that), and it will
get your stacked limits set appropriately.

3/ I just realised that raid0 is easier than I had previously
thought. We don't need the completely functional bio splitting
that dm has. We only need to be able to split a bio that has just
one page as the use of merge_bvec_fn will ensure that we never get
a larger bio that we cannot handle. And splitting a bio with only
one page is a lot easier. I now have code in my tree that
implements this quite cleanly and will probably post a patch
during the week.

- ideraid hasn't been ported to 2.5 at all yet.

- CD burning. There are still a few quirks to solve wrt SG_IO and ide-cd.

Jens: The basic hang has been solved (double fault in ide-cd), there still
seems to be some cases that don't work too well. Don't really have a
handle on those :/


- rmk: unconverted keyboard/mouse drivers (there's a deadline of 2.6.0
currently on these remaining in my/Linus' tree.)

- synaptic touchpad support


- rmk: UCB1[23]00 drivers, currently sitting in drivers/misc in the ARM
tree. (touchscreen, audio, gpio, type device.)


- rmk: network drivers. ARM people like to add tonnes of #ifdefs into
these to customise them to their hardware platform (eg, chip access
methods, addresses, etc.) I cope with this by not integrating them into my
tree. The result is that many ARM platforms can't be built from even my
tree without extra patches. This isn't sane, and has bred a culture of
network drivers not being submitted. I don't see this changing for 2.6


- dongle drivers need to be converted to sir-dev

- irport need to be converted to sir-kthread

- new drivers (irtty-sir/smsc-ircc2/donauboe) need more testing

- rmk: Refuse IrDA initialisation if sizeof(structures) is incorrect (I'm
not sure if we still need this; I think gcc 2.95.3 on ARM shows this
problem though.)


- alan: Some cardbus crashes the system

- alan: Hotplug locking is hosed


- alan: Most drivers crash the system on eject randomly with timer bugs. I
think after RMK's stuff is in most of the pcmcia/cardbus ones go except the
locking disaster.


- rmk: EPXA (ARM platform) PLD hotswap drivers (drivers/pld)


- Lots of drivers don't compile, others do but don't work.


- hch: large parts of the locking are hosed or not existant

(Mike Anderson, Patrick Mansfield, Badari Pulavarty)

- shost->my_devices isn't locked down at all

- the host list ist locked but not refcounted, mess can happen when the
spinlock is dropped

- there are lots of members of struct Scsi_Host/scsi_device/scsi_cmnd
with very unclear locking, many of them probably want to become
atomic_t's or bitmaps (for the 1bit bitfields).

- there's lots of volatile abuse in the scsi code that needs to be
thought about.

- there's some global variables incremented without any locks

- Convert am53c974, dpt_i2o, initio and pci2220i to DMA-mapping

- Make inia100, cpqfc, pci2000 and dc390t compile

- Convert

wd33c99 based: a2091 a3000 gpv11 mvme174 sgiwd93 53c7xx based:
amiga7xxx bvme6000 mvme16x initio am53c974 pci2000 pci2220i qla1280
sym53c8xx dc390t

To new error handling

I think the sym53c8xx could probably be pulled out of the tree because
the sym_2 replaces it. I'm also looking at converting the qla1280.

It also might be possible to shift the 53c7xx based drivers over to
53c700 which does the new EH stuff, but I don't have the hardware to check
such a shift.

For the non-compiling stuff, I've probably missed a few that just aren't
compilable on my platforms, so any updates would be welcome. Also, are
some of our non-compiling or unconverted drivers obsolete?


- rmk: SA11xx USB client/gadget code (David B has been doing some work on
this, and keeps trying to prod me, but unfortunately I haven't had the time
to look at his work, sorry David.)


- ext3 data=journal mode is bust.

- ext3/htree doesn't play right with NFS server. 90% fixed in -mm.

- AIO/direct-IO writes can race with truncate and wreck filesystems.

- Easy fix is to only allow the feature for S_ISBLK files.

- hch: devfs: there's a fundamental lookup vs devfsd race that's only
fixable by introducing a lookup vs devfs deadlock. I can't see how this is
fixable without getting rid of the current devfsd design. Mandrake seems
to have a workaround for this so this is at least not triggered so easily,
but that's not what I'd consider a fix..


- O(1) scheduler starvation, poor behaviour seems unresolved.

Jens: "I've been running 2.5.67-mm3 on my workstation for two days, and
it still doesn't feel as good as 2.4. It's not a disaster like some
revisisons ago, but it still has occasional CPU "stalls" where it feels
like a process waits for half a second of so for CPU time. That's is very

Also see Mike Galbraith's work.

- Alan: 32bit uid support is *still* broken for process accounting.

Create a 32bit uid, turn accounting on. Shock horror it doesn't work
because the field is 16bit. We need an acct structure flag day for 2.6


- Overcommit accounting gets wrong answers

- underestimates reclaimable slab, gives bogus failures when
dcache&icache are large.

- gets confused by reclaimable-but-not-freed truncated ext3 pages.
Lame fix exists in -mm.

- Proper user level no overcommit also requires a root margin adding



- The .modinfo patch needs to go in. It's trivial, but it's the major
missing functionality vs. 2.4. Keeps bouncing off Linus.

- __module_get(): "I know I have a refcount already and I don't care
if they're doing rmmod --wait, gimme.". Keeps bouncing off Linus.

- Per-cpu support inside modules (have patch, in testing).

- shemminger: The module remove rework that Rusty and Dave are working on
needs to be fixed before 2.6. Right now, it is impossible to write a
protocol or network device that can be safely unloaded when it is a module.




- UDP apps can in theory deadlock, because the ip_append_data path can end
up sleeping while the socket lock is held.

It is OK to sleep with the socket held held, normally. But in this case
the sleep happens while waiting for socket memory/space to become
available, if another context needs to take the socket lock to free up the
space we could hang.

I sent a rough patch on how to fix this to Alexey, and he is analyzing
the situation. I expect a final fix from him next week or so.

- Semantics for IPSEC during operations such as TCP connect suck currently.

When we first try to connect to a destination, we may need to ask the
IPSEC key management daemon to resolve the IPSEC routes for us. For the
purposes of what the kernel needs to do, you can think of it like ARP. We
can't send the packet out properly until we resolve the path.

What happens now for IPSEC is basically this:

O_NONBLOCK: returns -EAGAIN over and over until route is resolved

!O_NONBLOCK: Sleeps until route is resolved

These semantics are total crap. The solution, which Alexey is working
on, is to allow incomplete routes to exist. These "incomplete" routes
merely put the packet onto a "resolution queue", and once the key manager
does it's thing we finish the output of the packet. This is precisely how
ARP works.

I don't know when Alexey will be done with this.

- There are those mysterious TCP hangs of established state sockets.
Someone has to get a good log in order for us to effectively debug this.



- Handle non-linear skbs everywhere. This is going in via Dave now.

- Rework conntrack hashing.

- Module relationship bogosity fix (trivial, have patch).


- rmk: several OSS drivers for SA11xx-based hardware in need of
ALSA-ification and L3 bus support code for these.

- rmk: linux/sound/drivers/mpu401/mpu401.c and
linux/sound/drivers/virmidi.c complained about 'errno' at some time in the
past, need to confirm whether this is still a problem.

- rmk: need to complete ALSA-ification of the WaveArtist driver for both
NetWinder and other stuff (there's some fairly fundamental differences in
the way the mixer needs to be handled for the NetWinder.)


- Lots of 2.4 fixes including some security are not in 2.5

- There are about 60 or 70 security related checks that need doing
(copy_user etc) from Stanford tools

- A couple of hundred real looking bugzilla bugs

Not-ready features and speedups


- Framework for selecting IO schedulers. This is the main one really.
Once this is in place we can drop in new schedulers any old time, no risk.

- Runtime-selectable disk scheduler framework.

- Anticipatory scheduler. Working OK now, still has problems with seeky
OLTP-style loads.

- CFQ scheduler. Seems to work but Jens planning significant rework.

- The qlogic driver: needs work.


- reiserfs_file_write() speedup. There are concerns that some applications
do the wrong thing with large stat.st_blksize.

- ext3 lock_kernel() removal: that part works OK and is mergeable. But
we'll also need to make lock_journal() a spinlock, and that's deep surgery.

- 32bit quota needs a lot more testing but may work now

- Integrate Chris Mason's 2.4 reiserfs ordered data and data journaling
patches. They make reiserfs a lot safer.

- (Trond:) Yes: I'm still working on an atomic "open()", i.e. one
where we short-circuit the usual VFS path_walk() + lookup() +
permission() + create() + .... bullsh*t...

I have several reasons for wanting to do this (all of
them related to NFS of course, but much of the reasoning applies
to *all* networked file systems).

1) The above sequence is simply not atomic on *any* networked

2) It introduces a sh*tload of completely unnecessary RPC calls (why
do a 'permission' RPC call when the server is in *any* case going to
tell you whether or not this operations is allowed. Why do a
'lookup()' when the 'create()' call can be made to tell you whether or
not a file already exists).

3) It is incompatible with some operations: the current create()
doesn't pass an 'EXCLUSIVE' flag down to the filesystems.

4) (NFS specific?) open() has very different cache consistency
requirements when compared to most other VFS operations.

I'd very much like for something like Peter Braam's 'lookup with
intent' or (better yet) for a proper dentry->open() to be integrated with
path_walk()/open_namei(). I'm still working on the latter (Peter has
already completed the lookup with intent stuff).

- rmk: update acorn partition parsing code - making all acorn schemes
appear in check.c so we don't have to duplicate the scanning of multiple
types, and adding support for eesox partitions.



- Zippel's Reference count simplification. Tricky code, but cuts about 120
lines from module.c. Patch exists, needs stressing.

- /proc/kallsyms. What most people really wanted from /proc/ksyms. Patch

- Fix module-failed-init races by starting module "disabled". Patch
exists, requires some subsystems (ie. add_partition) to explicitly say
"make module live now". Without patch we are no worse off than 2.4 etc.

- Integrate userspace irq balancing daemon.

- kexec. Seems to work, is in -mm.

- rmk: modules / /proc/kcore / vmalloc This needs sorting and testing to
ensure that stuff like gdb vmlinux /proc/kcore works as expected. I
believe this is the only show stopper preventing any ARM platform being
built in Linus' kernel.

- rmk: lib/inflate.c must not use static variables (causes these to be
referenced via GOTOFF relocations in PIC decompressor. We have a PIC
decompressor to avoid having to hard code a per platform zImage link
address into the makefiles.)


- objrmap: concerns over page reclaim performance at high sharing levels,
and interoperation with nonlinear mappings is hairy.

- Readd and make /proc/sys/vm/freepages writable again so that boxes can be
tuned for heavy interrupt load.



- Real serious use of IPSEC is hampered by lack of MPLS support. MPLS is a
switching technology that works by switching based upon fixed length labels
prepended to packets. Many people use this and IPSEC to implement VPNs
over public networks, it is also used for things like traffic engineering.

A good reference site is:

Anyways, an existing (crappy) implementation exists. I've almost
completed a rewrite, I should have something in the tree next week.

- Sometimes we generate IP fragments when it truly isn't necessary.

The way IP fragmentation is specified, each fragment must be modulo 8
bytes in length. So suppose the device has an MTU that is not 0 modulo 8,
ethernet even classifies in this way. 1500 == (8 * 187) + 4

Our IP fragmenting engine can fragment on packets that are sized within
the last modulo 8 bytes of the MTU. This happens in obscure cases, but it
does happen.

I've proposed a fix to Alexey, whereby very late in the output path we
check the packet, if we fragmented but the data length would fit into the
MTU we unfragment the packet.

This is low priority, because technically it creates suboptimal behavior
rather than mis-operation.


- Lots of misc. cleanups, which are happening slowly.

- davem: Netfilter needs to stop linearizing packets as much as possible.

Zerocopy output packets are basically undone by netfilter becuase all of
it assumed it was working with linear socket buffers.

Rusty is fixing this piece by piece. He is nearly done with this work.

power management

(Pat) There is some preliminary work at bk://,
though I'm currently in the process of reworking it.

It includes:

- New device power management core code, both for individual devices,
and for global state transitions.

- A generic user interface for triggering system power state transitions.

- Arch-independent code for performing state transitions, that calls
platform-specific methods along the way.

- A better suspend-to-disk mechanism than swsusp.

There are various other details to be worked out, which are the real fun
part. And of course, driver support, but that is something that can happen
at any time.


- PCI locking

- Frame buffer restore codepaths (that requires some deep PCI magic)

- XFree86 hooks

- AGP restoration

- DRI restoration

- IDE suspend/resume without races (Ben is looking at this a little)

- How to deal with devices that babble (some stuff we have to global IRQ
off to save, and global IRQ on -after- we recover with APM)

- Pat's swsusp rework?

- Pat: There are already CPU device structures; MTRRs should be a
dynamically registered interface of CPUs, which implies there needs
to be some other glue to know that there are MTRRs that need to be


- Andi: i386 sub architectures for common boxes (in particular bigsmp and
summit) need to be runtime probed options, not compile time. Vendors
cannot ship an own kernel rpm for all these cases. (patch is in -mm, works

- Also PC9800 merge needs finishing to the point we want for 2.6 (not all).

- ES7000 wants merging (now we are all happy with it). That shouldn't be a
big problem.


- 64-bit dev_t. Seems almost ready, but it's not really known how much
work is still to do. Patches exist in -mm but with the recent rise of the
neo-viro I'm not sure where things are at.

- We need a kernel side API for reporting error events to userspace (could
be async to 2.6 itself)

(Prototype core based on netlink exists)

- Kai: Introduce a sane, easy and standard way to build external modules

- Kai: Allow separate src/objdir


- Alan: We have multiple drivers walking the pci device lists and also
using things like pci_find_device in unsafe ways with no refcounting. I
think we have to make pci_find_device etc refcount somewhere and add
pci_device_put as was done with networking.

- Some network drivers don't even build

- Alan: PCI hotplug is unsafe (locking is totally screwed)

- Ditto cardbus

- Alan: Cardbus/PCMCIA requires all Russell's stuff is merged to do
multiheader right and so on


- davej: ACPI has a number of failures right now. There are a number of
entries in bugzilla which could all be the same bug. It manifests as a
"network card doesn't recieve packets" booting with 'acpi=off noapic' fixes

alan: VIA APIC stuff is one bit of this, there are also some other
reports that were caused by ACPI not setting level v edge trigger some

- davej: There's also another nasty 'doesnt boot' bug which quite a few
people (myself included) are seeing on some boxes (especially laptops).


- Floppy is almost unusably buggy still


- Alan: Multiple serious bugs in the DRI drivers (most now with patches
thankfully). "The badness I know about is almost entirely IRQ mishandling.
DRI failing to mask PCI irqs on exit paths."

(might be fixed due to DRI updates?)

- Various suspect things in AGP.



- IDE requires bio walking

"Bartlomiej has IDE multisector working" (does that mean it's fixed?)

- IDE PIO has occasional unexplained PIO disk eating reports

- IDE has multiple zillions of races/hangs in 2.5 still

- IDE scsi needs rewriting

- IDE needs significant reworking to handle Simplex right

- IDE hotplug handling for 2.5 is completely broken still

- IDE tcq. Either kill it or fix it. Not a "big todo", as such.

- There are lots of other IDE bugs that wont go away until the taskfile
stuff is included, the locking bugs that allow any user to hang the IDE
layer in 2.5, and some other updates are forward ported. (esp. HPT372N).


(Kai, rmk)

- isdn_tty locking is completely broken (cli() and friends)

- fix lots of remaining bugs in the isdn link layer / hisax protocol layer
/ hisax subdrivers, so that at least 99% of the users have a usable ISDN

- fix other drivers

- lots more cleanups, adaption to recent APIs etc

- fixup tty-based ISDN drivers which provide TIOCM* ioctls (see my recent
3-set patch for serial stuff)

Alternatively, we could re-introduce the fallback to driver ioctl parsing
for these if not enough drivers get updated.


- davej: Either Wireless network drivers or PCMCIA broke somewhen. A
configuration that worked fine under 2.4 doesn't receive any packets. Need
to look into this more to make sure I don't have any misconfiguration that
just 'happened to work' under 2.4


- Half of SCSI doesn't compile


- 2.5.x won't boot on some 440GX

alan: Problem understood now, feasible fix in 2.4/2.4-ac. (440GX has two
IRQ routers, we use the $PIR table with the PIIX, but the 440GX doesnt use
the PIIX for its IRQ routing). Fall back to BIOS for 440GX works and Intel

- 2.5.x doesn't handle VIA APIC right yet.

1. We must write the PCI_INTERRUPT_LINE

2. We have quirk handlers that seem to trash it.

- ACPI needs the relax patches merging to work on lots of laptops

- ECC driver questions are not yet sorted (DaveJ is working on this)

- PC9800 is not fully merged - most of this I think is 2.7 stuff but a few
bits might be 2.6 candidate



- time handling is broken. Need to move up 2.4 time.c code.

- Another report of a crash at shutdown on Simics with no iommu when all
memory was used. Could be related to the one above.

- NMI watchdog seems to tick too fast

- some fixes from 2.4 still need to be merged

- not very well tested. probably more bugs lurking.

- 32bit vsyscalls seem to be broken

- 32bit elf coredumps are broken

- need to coredump 64bit vsyscall code with dwarf2

- move 64bit signal trampolines into vsyscall code and add dwarf2 for it.

- describe kernel assembly with dwarf2 annotations for kgdb (currently
waiting on some binutils changes for this)


- rmk: missing raw keyboard translation tables for all ARM machines.
Haven't even looked into this at all. This could be messy since there
isn't an ARM architecture standard. I'm presently hoping that it won't be
an issue. If it does, I guess we'll see drivers/char/keyboard.c explode.


- SH3/SH3-64 need resyncing, as do some other ports. No impact on
mainstream platforms hopefully.

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