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KernelJanitors/Todo

Before attacking any of these, we suggest sending a few patches in advance to see if you are doing something wrong, or if someone else is already doing same work.

Read related threads in the mailing list archive.

Where it makes sense, sections are supposed to be ordered by increasing difficulty.

Send patches that add/fix items to kernel-janitors@vger.kernel.org.

Links should be marked with:

D: description/information about the issue

E: example patch


NOTE: Search & Replace

Sometimes all your patch will do is simply changing one function to another. Doing this is especially tempting in "convert to new API" section. History shows this is often wrong: old bugs are not fixed, new bugs are introduced.

If all your patch does is search & replace, double check. If in doubt, ask on mailing list.

* add more checks to kj.pl

Task Type

Current List

Audit return codes

/ReturnCodes

Function balancing

/FunctionBalancing

Old/New functions

/ApiChanges

* printk() calls should include appropriate KERN_* constant (of course

  • only at beginning of lines). Also consider using dev_printk() and friends.

* pr_debug() from kernel.h could replace a lot of DPRINTK and similar macros.

* same for pr_info()

* Lots of unnecessary casts (mostly void* pointers) in drivers can be removed.

  • Example:

  - struct netdev_private *np = (struct netdev_private *)dev->priv;
  + struct netdev_private *np = dev->priv;

* ARRAY_SIZE macro has duplicates, remove them.

  • (2007/10/27 - the 4 remaining duplicate defs have good reasons for existing. Someone please verify agreement and then remove this todo item)

* put BIT macro into kernel.h (?) and remove it from drivers

* Purely cosmetic, but far nicer to read.

  - for (list = ymf_devs.next; list != &ymf_devs; list = list->next) {
  + list_for_each(list, &ymf_devs) {

* Convert comments to C99 initializers:

        -       /* 10 */ DECLARE_PIIX_DEV("ICH2"),
        +       [10] = DECLARE_PIIX_DEV("ICH2"),
                        (if order matters)
  • or

        -       15, /* foo */
        +       .foo = 15,

* make non-global functions static.

* convert all explicit lock initializations to spin_lock_init() or

* fix compilation warnings/errors - be careful because the cause of some warnings/errors aren't as obvious as they seem, and fixes can cause bugs

* pci_set_dma_mask() and friends should use DMA_BIT_MASK(nn) instead of

* check kmallocs for things like GFP_DMA without a memtype.

* check that a freed pointer (*kfree_*) is not used again.

* make sure BUG() is used correctly (i.e. if(function()) BUG(); is evil)

  • i.e. even when no-op-ing BUG we still have an if (See also: BUG_ON)

* Code in wrong sections (ie. __init code called from __exit):

* Fix gcc 4 warnings.

* Audit all memcpy and memmove calls.

  • If areas overlap memmove should be used, if they don't -- memcpy.

* drivers/char/i8k.c duplicates drivers/firmware/dmi_scan.c

  • Better would be to have dmi_scan.c set a flag which the i8k driver checks.

* sleeping functions should not be called in interrupts or under spinlocks:

  • copy_to/from_user(), put/get_user(), schedule(), kmalloc() except for GPF_ATOMIC, functions with __might_sleep() in body...

* go through all the tty/serial drivers and make sure they don't give out excessively useful information to non CAP_SYS_RAWIO users, then loosen permissions.

* check that buffers used in copy_to_user() don't leak information.

* check for dev_close calls without rtnl_lock held (causes assertion

  • failures).

* timer_del() vs. timer_del_sync()

* fix watchdog drivers to use link order rather than explicit

  • initialization calls (i810 is particularly broken)

* check stack usage (make checkstack) and reduce it in the worst cases.


SUSPECTS:

copy_to/from_user:

- look at drivers/char/n_tty.c

Items with longer description in no particular order:


Date: Wed, 14 Feb 2001 12:51:53 +0100 From: Manfred Spraul

bug in network drivers:

* dev->mem_start: NULL means "not command line configuration" 0xffffffff means "default". several drivers only check for NULL, not for 0xffffffff.

And then: Date: Wed, 14 Feb 2001 05:54:34 -0600 (CST) From: Jeff Garzik

netdev->mem_start is unsigned long... Should the test be for ~0 instead? The value 0xFFFFFFFF seems wrong for 64-bit machines.


- drivers that try to find multiple boards, possibly successfully allocating

  • for the first ones, then failing for, lets say, the third board, then it just returns failure for init_module, the module is unloaded but the resources remain allocated... in these cases we need to rollback the allocations, freeing it before returning from init_module or equivalent.


From: Hans Grobler

- audit ioctl functions to make sure there is no way a user can crash the machine or do sensitive stuff. For example, check for the necessary capabilities. Check that no userspace pointers are accessed directly. be careful with this... it takes a while to figure out which ioctls are covered by the parent ioctl function (these can be nested to great depths).


Date: Mon, 26 Feb 2001 16:53:50 -0800 (PST) From: "David S. Miller"

Andrew Morton writes:

  • > Could this be a driver problem?

    > netif_rx(skb); ... > new_skb = skb;

This is illegal and broken and will never work.

Once you give an skb to netif_rx() it is not yours to reference any longer.

Donald Becker added:

Easier fix:

-   np->stats.rx_bytes += skb->len;
+   np->stats.rx_bytes += pkt_len;

Grouping the writes to np->stats results in better cache usage.

Jeff Garzik added:

It makes use of the existing local 'pkt_len', and it checks off another item.


From Dave Jones

- Lots of drivers are doing evil looking things writing to PCI_CACHE_LINE_SIZE

  • This should be done during PCI initialisation.

- Many drivers have alignments such as..

  • dev->priv = (void *)(((unsigned long)dev->priv + 7) & ~7); jgarzik:

    • What they are doing here is DMA'ing into their private board (dev->priv), which is wrong -- they should be using PCI DMA instead. They can't use init_etherdev because it doesn't pass GFP_DMA to kmalloc for dev->priv, and since they are DMA'ing into dev->priv, they have to do things manually.

- Signedness issues. We have _lots_ of these.

  • Adding a -W to the kernel build line shows them. We have lots of code paths that are not executed because comparisons <0 on an unsigned int always evaluates to true.

    We also need to check for things like...

  char foo[4]={1,2,3,133}; /* 133 in signed char!*/

From: Jeff Garzik

1) The string form

        [const] char *foo = "blah";

creates two variables in the final assembly output, a static string, and a char pointer to the static string. The alternate string form

        [const] char foo[] = "blah";

is better because it declares a single variable.

For variables marked __initdata, the "*foo" form causes only the pointer, not the string itself, to be dropped from the kernel image, which is a bug. Using the "foo[]" form with regular 'ole local variables also makes the assembly shorter.

2) "unsigned int" is preferred to "int", it generates better asm code on all platforms except sh5. This replacement needs to be done manually, because often 'int' is required due to negative values -Exxx commonly passed as error values.


From: Greg KH

- delete all pci_find_* functions from the kernel tree. Instead of pci_find_device use pci_get_device().

> Looking at pci.txt, it appears that if I use pci_get_device(), I will > also need to use pci_dev_put().

also check using the proper shutdown callback.


1. Fix sparse warnings.

Read section "Where to get sparse" in Documentation/sparse.txt. $ make allyesconfig or whatever config you like. Set CONFIG_DEBUG_INFO=n to make compiles faster and smaller.

$ make -k C=1 2>&1 | tee ../W_sparse
  • or

$ make -k C=1 CF=-D__CHECK_ENDIAN__ 2>&1 | tee ../W_sparse

_Plenty_ of patches here (well, not all of them fix sparse warnings ;-) ): [E: http://linux.bkbits.net:8080/linux-2.6/search/?PAGE=search&EXPR=sparse&SEARCH=ChangeSet+comments]

2. For portability reasons pointers should be printed as ("%p", ptr), not ("%08x", (int) ptr) or similar.

3.

$ make randconfig
$ make -k 2>&1 | tee ../W_randconfig

Find out why it doesn't build. Fix warnings that aren't seen with usual "allyesconfig", "allmodconfig", ...

P. S.: Run it several times, think a little and take bets on whether it'll build or not on the next party among local linuxoids. :-)

4. Some drivers do:

        if ((jiffies - data->last_updated > HZ * 2) ||
            (jiffies < data->last_updated))

Should be:

        #include <linux/jiffies.h>
        if (time_after(jiffies, data->last_updated + HZ * 2))

[E: http://linux.bkbits.net:8080/linux-2.6/?PAGE=gnupatch&REV=42261f25iCdhlwTMywIQxvBDrIHj1A]

5.

Some function prototypes (in both .h and .c files) specify attributes like __init and __exit in the prototype. gcc (at least at 3.3.3) uses the last such attribute that is actually specified, without issuing a warning. So we can have:

* Prototype declarations that use one attribute and a function body that uses another attribute.

* Functions that from the .c code appear to be normal text but the .h file is silently setting a special attribute.

  • Both are potential sources of programmer confusion or bugs.

Identify: * all places where attributes in prototype and function definition don't match (choose the correct one, move it to declaration), * all places where prototype contains attribute but definition doesn't (move it to declaration).

  • The same task should not be done for extern data declarations because of FRV.

Once that is done, remove #include <linux/init.h> from all .h files. Only .[cS] files should specify which section the data and text are stored in, .h files should only define the C language information.

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last edited 2009-04-20 14:59:47 by HenrikKretzschmar