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;}}} use `netdev_priv()` for network devices See /VoidPointerConvs for more details. * `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 `rwlock_init()`. (Besides consistency this also helps automatic lock validators and debugging code.) [D: http://lwn.net/Articles/109505/] [E: http://linux.bkbits.net:8080/linux-2.6/cset@419a6f292wHnthuDzw7VfgECNLmvLg?nav=index.html|ChangeSet@-8w] * 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_{32,64}BIT_MASK` instead of `0xffff`... This is not 2.4 compatible, so beware of drivers with same code. [D: http://marc.theaimsgroup.com/?t=108001993000001] Don't forget to #include dma-mapping.h * 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`): Run `make buildcheck` to find offending code. (`read_eeprom` in net drivers is a good candidate for `__init`) [D: http://marc.theaimsgroup.com/?l=kernel-janitor-discuss&m=108640220401558] * Fix gcc 4 warnings. [D: http://marc.theaimsgroup.com/?t=110348353800003] Note: Set `CONFIG_DEBUG_INFO=n` to make compiles faster and smaller. * Audit all `memcpy` and `memmove` calls. If areas overlap `memmove` should be used, if they don't -- `memcpy`. * `drivers/char/i8k.c` duplicates `arch/i386/kernel/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. [D: http://lkml.org/lkml/2005/1/17/94] * 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()` [D: http://www.uwsg.iu.edu/hypermail/linux/kernel/0005.3/0269.html] A lot of the timer deletion races are hard to fix because of the deadlock problem. * 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. [D: http://bugme.osdl.org/show_bug.cgi?id=386] [D: http://marc.theaimsgroup.com/?l=kernel-janitor-discuss&m=110661227615538] ----------------------------------------------------------------------------- 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. - `sound/oss/maestro3.c` doesn't `pci_free_consistent` any buffers if one allocation fails, but others succeeded. ----------------------------------------------------------------------------- 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: Jeff Garzik > It is highly recommended to always compile with CONFIG_ISAPNP=y due > to these differences. If you grep around for CONFIG_ISAPNP versus > CONFIG_ISAPNP_MODULE, you'll see that many drivers are woefully > unprepared for isapnp support compiled as a module. Yep.. grep for CONFIG_ISAPNP, look at the code, and evaluate it to make sure that isapnp works for that drivers regardless of whether CONFIG_ISAPNP -or- CONFIG_ISAPNP_MODULE is defined. ----------------------------------------------------------------------------- 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 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 ` 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.