2
0
mirror of https://github.com/edk2-porting/linux-next.git synced 2024-12-17 09:43:59 +08:00
Mainline Linux tree for various devices, only for fun :)
Go to file
Minchan Kim 04c8716f7b mm: try to exhaust highatomic reserve before the OOM
I got OOM report from production team with v4.4 kernel.  It had enough
free memory but failed to allocate GFP_KERNEL order-0 page and finally
encountered OOM kill.  It occured during QA process which launches
several apps, switching and so on.  It happned rarely.  IOW, In normal
situation, it was not a problem but if we are unluck so that several
apps uses peak memory at the same time, it can happen.  If we manage to
pass the phase, the system can go working well.

I could reproduce it with my test(memory spike easily.  Look at below.

The reason is free pages(19M) of DMA32 zone are reserved for
HIGHORDERATOMIC and doesn't unreserved before the OOM.

  balloon invoked oom-killer: gfp_mask=0x24280ca(GFP_HIGHUSER_MOVABLE|__GFP_ZERO), order=0, oom_score_adj=0
  balloon cpuset=/ mems_allowed=0
  CPU: 1 PID: 8473 Comm: balloon Tainted: G        W  OE   4.8.0-rc7-00219-g3f74c9559583-dirty #3161
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
  Call Trace:
    dump_stack+0x63/0x90
    dump_header+0x5c/0x1ce
    oom_kill_process+0x22e/0x400
    out_of_memory+0x1ac/0x210
    __alloc_pages_nodemask+0x101e/0x1040
    handle_mm_fault+0xa0a/0xbf0
    __do_page_fault+0x1dd/0x4d0
    trace_do_page_fault+0x43/0x130
    do_async_page_fault+0x1a/0xa0
    async_page_fault+0x28/0x30
  Mem-Info:
  active_anon:383949 inactive_anon:106724 isolated_anon:0
   active_file:15 inactive_file:44 isolated_file:0
   unevictable:0 dirty:0 writeback:24 unstable:0
   slab_reclaimable:2483 slab_unreclaimable:3326
   mapped:0 shmem:0 pagetables:1906 bounce:0
   free:6898 free_pcp:291 free_cma:0
  Node 0 active_anon:1535796kB inactive_anon:426896kB active_file:60kB inactive_file:176kB unevictable:0kB isolated(anon):0kB isolated(file):0kB mapped:0kB dirty:0kB writeback:96kB shmem:0kB writeback_tmp:0kB unstable:0kB pages_scanned:1418 all_unreclaimable? no
  DMA free:8188kB min:44kB low:56kB high:68kB active_anon:7648kB inactive_anon:0kB active_file:0kB inactive_file:4kB unevictable:0kB writepending:0kB present:15992kB managed:15908kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:20kB kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
  lowmem_reserve[]: 0 1952 1952 1952
  DMA32 free:19404kB min:5628kB low:7624kB high:9620kB active_anon:1528148kB inactive_anon:426896kB active_file:60kB inactive_file:420kB unevictable:0kB writepending:96kB present:2080640kB managed:2030092kB mlocked:0kB slab_reclaimable:9932kB slab_unreclaimable:13284kB kernel_stack:2496kB pagetables:7624kB bounce:0kB free_pcp:900kB local_pcp:112kB free_cma:0kB
  lowmem_reserve[]: 0 0 0 0
  DMA: 0*4kB 0*8kB 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 2*4096kB (H) = 8192kB
  DMA32: 7*4kB (H) 8*8kB (H) 30*16kB (H) 31*32kB (H) 14*64kB (H) 9*128kB (H) 2*256kB (H) 2*512kB (H) 4*1024kB (H) 5*2048kB (H) 0*4096kB = 19484kB
  51131 total pagecache pages
  50795 pages in swap cache
  Swap cache stats: add 3532405601, delete 3532354806, find 124289150/1822712228
  Free swap  = 8kB
  Total swap = 255996kB
  524158 pages RAM
  0 pages HighMem/MovableOnly
  12658 pages reserved
  0 pages cma reserved
  0 pages hwpoisoned

Another example exceeded the limit by the race is

  in:imklog: page allocation failure: order:0, mode:0x2280020(GFP_ATOMIC|__GFP_NOTRACK)
  CPU: 0 PID: 476 Comm: in:imklog Tainted: G            E   4.8.0-rc7-00217-g266ef83c51e5-dirty #3135
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
  Call Trace:
    dump_stack+0x63/0x90
    warn_alloc_failed+0xdb/0x130
    __alloc_pages_nodemask+0x4d6/0xdb0
    new_slab+0x339/0x490
    ___slab_alloc.constprop.74+0x367/0x480
    __slab_alloc.constprop.73+0x20/0x40
    __kmalloc+0x1a4/0x1e0
    alloc_indirect.isra.14+0x1d/0x50
    virtqueue_add_sgs+0x1c4/0x470
    __virtblk_add_req+0xae/0x1f0
    virtio_queue_rq+0x12d/0x290
    __blk_mq_run_hw_queue+0x239/0x370
    blk_mq_run_hw_queue+0x8f/0xb0
    blk_mq_insert_requests+0x18c/0x1a0
    blk_mq_flush_plug_list+0x125/0x140
    blk_flush_plug_list+0xc7/0x220
    blk_finish_plug+0x2c/0x40
    __do_page_cache_readahead+0x196/0x230
    filemap_fault+0x448/0x4f0
    ext4_filemap_fault+0x36/0x50
    __do_fault+0x75/0x140
    handle_mm_fault+0x84d/0xbe0
    __do_page_fault+0x1dd/0x4d0
    trace_do_page_fault+0x43/0x130
    do_async_page_fault+0x1a/0xa0
    async_page_fault+0x28/0x30
  Mem-Info:
  active_anon:363826 inactive_anon:121283 isolated_anon:32
   active_file:65 inactive_file:152 isolated_file:0
   unevictable:0 dirty:0 writeback:46 unstable:0
   slab_reclaimable:2778 slab_unreclaimable:3070
   mapped:112 shmem:0 pagetables:1822 bounce:0
   free:9469 free_pcp:231 free_cma:0
  Node 0 active_anon:1455304kB inactive_anon:485132kB active_file:260kB inactive_file:608kB unevictable:0kB isolated(anon):128kB isolated(file):0kB mapped:448kB dirty:0kB writeback:184kB shmem:0kB writeback_tmp:0kB unstable:0kB pages_scanned:13641 all_unreclaimable? no
  DMA free:7748kB min:44kB low:56kB high:68kB active_anon:7944kB inactive_anon:104kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:15992kB managed:15908kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:108kB kernel_stack:0kB pagetables:4kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
  lowmem_reserve[]: 0 1952 1952 1952
  DMA32 free:30128kB min:5628kB low:7624kB high:9620kB active_anon:1447360kB inactive_anon:485028kB active_file:260kB inactive_file:608kB unevictable:0kB writepending:184kB present:2080640kB managed:2030132kB mlocked:0kB slab_reclaimable:11112kB slab_unreclaimable:12172kB kernel_stack:2400kB pagetables:7284kB bounce:0kB free_pcp:924kB local_pcp:72kB free_cma:0kB
  lowmem_reserve[]: 0 0 0 0
  DMA: 7*4kB (UE) 3*8kB (UH) 1*16kB (M) 0*32kB 2*64kB (U) 1*128kB (M) 1*256kB (U) 0*512kB 1*1024kB (U) 1*2048kB (U) 1*4096kB (H) = 7748kB
  DMA32: 10*4kB (H) 3*8kB (H) 47*16kB (H) 38*32kB (H) 5*64kB (H) 1*128kB (H) 2*256kB (H) 3*512kB (H) 3*1024kB (H) 3*2048kB (H) 4*4096kB (H) = 30128kB
  2775 total pagecache pages
  2536 pages in swap cache
  Swap cache stats: add 206786828, delete 206784292, find 7323106/106686077
  Free swap  = 108744kB
  Total swap = 255996kB
  524158 pages RAM
  0 pages HighMem/MovableOnly
  12648 pages reserved
  0 pages cma reserved
  0 pages hwpoisoned

It's weird to show that zone has enough free memory above min watermark
but OOMed with 4K GFP_KERNEL allocation due to reserved highatomic
pages.  As last resort, try to unreserve highatomic pages again and if
it has moved pages to non-highatmoc free list, retry reclaim once more.

Link: http://lkml.kernel.org/r/1476259429-18279-4-git-send-email-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Sangseok Lee <sangseok.lee@lge.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-12-12 18:55:07 -08:00
arch m32r: fix build warning 2016-12-12 18:55:06 -08:00
block Don't feed anything but regular iovec's to blk_rq_map_user_iov 2016-12-07 08:23:35 -08:00
certs certs: Add a secondary system keyring that can be added to dynamically 2016-04-11 22:48:09 +01:00
crypto Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2016-12-10 16:21:55 -05:00
Documentation Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2016-12-12 10:48:02 -08:00
drivers drivers/pcmcia/m32r_pcc.c: check return from add_pcc_socket 2016-12-12 18:55:06 -08:00
firmware WHENCE: use https://linuxtv.org for LinuxTV URLs 2015-12-04 10:35:11 -02:00
fs ocfs2: replace CURRENT_TIME macro 2016-12-12 18:55:06 -08:00
include prctl: remove one-shot limitation for changing exe link 2016-12-12 18:55:06 -08:00
init Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2016-12-03 12:29:53 -05:00
ipc sched/wake_q: Rename WAKE_Q to DEFINE_WAKE_Q 2016-11-21 10:29:01 +01:00
kernel prctl: remove one-shot limitation for changing exe link 2016-12-12 18:55:06 -08:00
lib Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2016-12-12 10:48:02 -08:00
mm mm: try to exhaust highatomic reserve before the OOM 2016-12-12 18:55:07 -08:00
net Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2016-12-12 10:48:02 -08:00
samples bpf: xdp: Add XDP example for head adjustment 2016-12-08 14:25:13 -05:00
scripts scripts/tags.sh: handle OMAP platforms properly 2016-12-12 18:55:06 -08:00
security apparmor: fix change_hat not finding hat after policy replacement 2016-11-21 18:01:28 +11:00
sound dbri: move dereference after check for NULL 2016-12-06 12:18:22 -05:00
tools Merge branch 'perf-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2016-12-12 11:46:21 -08:00
usr usr/Kconfig: make initrd compression algorithm selection not expert 2014-12-13 12:42:52 -08:00
virt Merge branch 'linus' into locking/core, to pick up fixes 2016-12-11 13:07:13 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Merge branch 'misc' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild 2016-08-02 16:48:52 -04:00
.mailmap Merge branch 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus 2016-10-15 09:26:12 -07:00
COPYING
CREDITS Fix up a couple of field names in the CREDITS file 2016-12-02 10:48:50 -08:00
Kbuild scripts/gdb: provide linux constants 2016-05-23 17:04:14 -07:00
Kconfig kbuild: migrate all arch to the kconfig mainmenu upgrade 2010-09-19 22:54:11 -04:00
MAINTAINERS Merge branch 'efi-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2016-12-12 10:03:44 -08:00
Makefile Linux 4.9 2016-12-11 11:17:54 -08:00
README README: Delete obsolete i386 info + update arch/i386/ paths 2016-08-14 12:24:56 -06:00
REPORTING-BUGS Docs: fix missing word in REPORTING-BUGS 2016-02-15 11:18:23 +01:00

        Linux kernel release 4.x <http://kernel.org/>

These are the release notes for Linux version 4.  Read them carefully,
as they tell you what this is all about, explain how to install the
kernel, and what to do if something goes wrong.

WHAT IS LINUX?

  Linux is a clone of the operating system Unix, written from scratch by
  Linus Torvalds with assistance from a loosely-knit team of hackers across
  the Net. It aims towards POSIX and Single UNIX Specification compliance.

  It has all the features you would expect in a modern fully-fledged Unix,
  including true multitasking, virtual memory, shared libraries, demand
  loading, shared copy-on-write executables, proper memory management,
  and multistack networking including IPv4 and IPv6.

  It is distributed under the GNU General Public License - see the
  accompanying COPYING file for more details.

ON WHAT HARDWARE DOES IT RUN?

  Although originally developed first for 32-bit x86-based PCs (386 or higher),
  today Linux also runs on (at least) the Compaq Alpha AXP, Sun SPARC and
  UltraSPARC, Motorola 68000, PowerPC, PowerPC64, ARM, Hitachi SuperH, Cell,
  IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DEC VAX, AMD x86-64, AXIS CRIS,
  Xtensa, Tilera TILE, AVR32, ARC and Renesas M32R architectures.

  Linux is easily portable to most general-purpose 32- or 64-bit architectures
  as long as they have a paged memory management unit (PMMU) and a port of the
  GNU C compiler (gcc) (part of The GNU Compiler Collection, GCC). Linux has
  also been ported to a number of architectures without a PMMU, although
  functionality is then obviously somewhat limited.
  Linux has also been ported to itself. You can now run the kernel as a
  userspace application - this is called UserMode Linux (UML).

DOCUMENTATION:

 - There is a lot of documentation available both in electronic form on
   the Internet and in books, both Linux-specific and pertaining to
   general UNIX questions.  I'd recommend looking into the documentation
   subdirectories on any Linux FTP site for the LDP (Linux Documentation
   Project) books.  This README is not meant to be documentation on the
   system: there are much better sources available.

 - There are various README files in the Documentation/ subdirectory:
   these typically contain kernel-specific installation notes for some
   drivers for example. See Documentation/00-INDEX for a list of what
   is contained in each file.  Please read the Changes file, as it
   contains information about the problems, which may result by upgrading
   your kernel.

 - The Documentation/DocBook/ subdirectory contains several guides for
   kernel developers and users.  These guides can be rendered in a
   number of formats:  PostScript (.ps), PDF, HTML, & man-pages, among others.
   After installation, "make psdocs", "make pdfdocs", "make htmldocs",
   or "make mandocs" will render the documentation in the requested format.

INSTALLING the kernel source:

 - If you install the full sources, put the kernel tarball in a
   directory where you have permissions (e.g. your home directory) and
   unpack it:

     xz -cd linux-4.X.tar.xz | tar xvf -

   Replace "X" with the version number of the latest kernel.

   Do NOT use the /usr/src/linux area! This area has a (usually
   incomplete) set of kernel headers that are used by the library header
   files.  They should match the library, and not get messed up by
   whatever the kernel-du-jour happens to be.

 - You can also upgrade between 4.x releases by patching.  Patches are
   distributed in the xz format.  To install by patching, get all the
   newer patch files, enter the top level directory of the kernel source
   (linux-4.X) and execute:

     xz -cd ../patch-4.x.xz | patch -p1

   Replace "x" for all versions bigger than the version "X" of your current
   source tree, _in_order_, and you should be ok.  You may want to remove
   the backup files (some-file-name~ or some-file-name.orig), and make sure
   that there are no failed patches (some-file-name# or some-file-name.rej).
   If there are, either you or I have made a mistake.

   Unlike patches for the 4.x kernels, patches for the 4.x.y kernels
   (also known as the -stable kernels) are not incremental but instead apply
   directly to the base 4.x kernel.  For example, if your base kernel is 4.0
   and you want to apply the 4.0.3 patch, you must not first apply the 4.0.1
   and 4.0.2 patches. Similarly, if you are running kernel version 4.0.2 and
   want to jump to 4.0.3, you must first reverse the 4.0.2 patch (that is,
   patch -R) _before_ applying the 4.0.3 patch. You can read more on this in
   Documentation/applying-patches.txt

   Alternatively, the script patch-kernel can be used to automate this
   process.  It determines the current kernel version and applies any
   patches found.

     linux/scripts/patch-kernel linux

   The first argument in the command above is the location of the
   kernel source.  Patches are applied from the current directory, but
   an alternative directory can be specified as the second argument.

 - Make sure you have no stale .o files and dependencies lying around:

     cd linux
     make mrproper

   You should now have the sources correctly installed.

SOFTWARE REQUIREMENTS

   Compiling and running the 4.x kernels requires up-to-date
   versions of various software packages.  Consult
   Documentation/Changes for the minimum version numbers required
   and how to get updates for these packages.  Beware that using
   excessively old versions of these packages can cause indirect
   errors that are very difficult to track down, so don't assume that
   you can just update packages when obvious problems arise during
   build or operation.

BUILD directory for the kernel:

   When compiling the kernel, all output files will per default be
   stored together with the kernel source code.
   Using the option "make O=output/dir" allows you to specify an alternate
   place for the output files (including .config).
   Example:

     kernel source code: /usr/src/linux-4.X
     build directory:    /home/name/build/kernel

   To configure and build the kernel, use:

     cd /usr/src/linux-4.X
     make O=/home/name/build/kernel menuconfig
     make O=/home/name/build/kernel
     sudo make O=/home/name/build/kernel modules_install install

   Please note: If the 'O=output/dir' option is used, then it must be
   used for all invocations of make.

CONFIGURING the kernel:

   Do not skip this step even if you are only upgrading one minor
   version.  New configuration options are added in each release, and
   odd problems will turn up if the configuration files are not set up
   as expected.  If you want to carry your existing configuration to a
   new version with minimal work, use "make oldconfig", which will
   only ask you for the answers to new questions.

 - Alternative configuration commands are:

     "make config"      Plain text interface.

     "make menuconfig"  Text based color menus, radiolists & dialogs.

     "make nconfig"     Enhanced text based color menus.

     "make xconfig"     Qt based configuration tool.

     "make gconfig"     GTK+ based configuration tool.

     "make oldconfig"   Default all questions based on the contents of
                        your existing ./.config file and asking about
                        new config symbols.

     "make silentoldconfig"
                        Like above, but avoids cluttering the screen
                        with questions already answered.
                        Additionally updates the dependencies.

     "make olddefconfig"
                        Like above, but sets new symbols to their default
                        values without prompting.

     "make defconfig"   Create a ./.config file by using the default
                        symbol values from either arch/$ARCH/defconfig
                        or arch/$ARCH/configs/${PLATFORM}_defconfig,
                        depending on the architecture.

     "make ${PLATFORM}_defconfig"
                        Create a ./.config file by using the default
                        symbol values from
                        arch/$ARCH/configs/${PLATFORM}_defconfig.
                        Use "make help" to get a list of all available
                        platforms of your architecture.

     "make allyesconfig"
                        Create a ./.config file by setting symbol
                        values to 'y' as much as possible.

     "make allmodconfig"
                        Create a ./.config file by setting symbol
                        values to 'm' as much as possible.

     "make allnoconfig" Create a ./.config file by setting symbol
                        values to 'n' as much as possible.

     "make randconfig"  Create a ./.config file by setting symbol
                        values to random values.

     "make localmodconfig" Create a config based on current config and
                           loaded modules (lsmod). Disables any module
                           option that is not needed for the loaded modules.

                           To create a localmodconfig for another machine,
                           store the lsmod of that machine into a file
                           and pass it in as a LSMOD parameter.

                   target$ lsmod > /tmp/mylsmod
                   target$ scp /tmp/mylsmod host:/tmp

                   host$ make LSMOD=/tmp/mylsmod localmodconfig

                           The above also works when cross compiling.

     "make localyesconfig" Similar to localmodconfig, except it will convert
                           all module options to built in (=y) options.

   You can find more information on using the Linux kernel config tools
   in Documentation/kbuild/kconfig.txt.

 - NOTES on "make config":

    - Having unnecessary drivers will make the kernel bigger, and can
      under some circumstances lead to problems: probing for a
      nonexistent controller card may confuse your other controllers

    - A kernel with math-emulation compiled in will still use the
      coprocessor if one is present: the math emulation will just
      never get used in that case.  The kernel will be slightly larger,
      but will work on different machines regardless of whether they
      have a math coprocessor or not.

    - The "kernel hacking" configuration details usually result in a
      bigger or slower kernel (or both), and can even make the kernel
      less stable by configuring some routines to actively try to
      break bad code to find kernel problems (kmalloc()).  Thus you
      should probably answer 'n' to the questions for "development",
      "experimental", or "debugging" features.

COMPILING the kernel:

 - Make sure you have at least gcc 3.2 available.
   For more information, refer to Documentation/Changes.

   Please note that you can still run a.out user programs with this kernel.

 - Do a "make" to create a compressed kernel image. It is also
   possible to do "make install" if you have lilo installed to suit the
   kernel makefiles, but you may want to check your particular lilo setup first.

   To do the actual install, you have to be root, but none of the normal
   build should require that. Don't take the name of root in vain.

 - If you configured any of the parts of the kernel as `modules', you
   will also have to do "make modules_install".

 - Verbose kernel compile/build output:

   Normally, the kernel build system runs in a fairly quiet mode (but not
   totally silent).  However, sometimes you or other kernel developers need
   to see compile, link, or other commands exactly as they are executed.
   For this, use "verbose" build mode.  This is done by passing
   "V=1" to the "make" command, e.g.

     make V=1 all

   To have the build system also tell the reason for the rebuild of each
   target, use "V=2".  The default is "V=0".

 - Keep a backup kernel handy in case something goes wrong.  This is
   especially true for the development releases, since each new release
   contains new code which has not been debugged.  Make sure you keep a
   backup of the modules corresponding to that kernel, as well.  If you
   are installing a new kernel with the same version number as your
   working kernel, make a backup of your modules directory before you
   do a "make modules_install".

   Alternatively, before compiling, use the kernel config option
   "LOCALVERSION" to append a unique suffix to the regular kernel version.
   LOCALVERSION can be set in the "General Setup" menu.

 - In order to boot your new kernel, you'll need to copy the kernel
   image (e.g. .../linux/arch/x86/boot/bzImage after compilation)
   to the place where your regular bootable kernel is found.

 - Booting a kernel directly from a floppy without the assistance of a
   bootloader such as LILO, is no longer supported.

   If you boot Linux from the hard drive, chances are you use LILO, which
   uses the kernel image as specified in the file /etc/lilo.conf.  The
   kernel image file is usually /vmlinuz, /boot/vmlinuz, /bzImage or
   /boot/bzImage.  To use the new kernel, save a copy of the old image
   and copy the new image over the old one.  Then, you MUST RERUN LILO
   to update the loading map! If you don't, you won't be able to boot
   the new kernel image.

   Reinstalling LILO is usually a matter of running /sbin/lilo.
   You may wish to edit /etc/lilo.conf to specify an entry for your
   old kernel image (say, /vmlinux.old) in case the new one does not
   work.  See the LILO docs for more information.

   After reinstalling LILO, you should be all set.  Shutdown the system,
   reboot, and enjoy!

   If you ever need to change the default root device, video mode,
   ramdisk size, etc.  in the kernel image, use the 'rdev' program (or
   alternatively the LILO boot options when appropriate).  No need to
   recompile the kernel to change these parameters.

 - Reboot with the new kernel and enjoy.

IF SOMETHING GOES WRONG:

 - If you have problems that seem to be due to kernel bugs, please check
   the file MAINTAINERS to see if there is a particular person associated
   with the part of the kernel that you are having trouble with. If there
   isn't anyone listed there, then the second best thing is to mail
   them to me (torvalds@linux-foundation.org), and possibly to any other
   relevant mailing-list or to the newsgroup.

 - In all bug-reports, *please* tell what kernel you are talking about,
   how to duplicate the problem, and what your setup is (use your common
   sense).  If the problem is new, tell me so, and if the problem is
   old, please try to tell me when you first noticed it.

 - If the bug results in a message like

     unable to handle kernel paging request at address C0000010
     Oops: 0002
     EIP:   0010:XXXXXXXX
     eax: xxxxxxxx   ebx: xxxxxxxx   ecx: xxxxxxxx   edx: xxxxxxxx
     esi: xxxxxxxx   edi: xxxxxxxx   ebp: xxxxxxxx
     ds: xxxx  es: xxxx  fs: xxxx  gs: xxxx
     Pid: xx, process nr: xx
     xx xx xx xx xx xx xx xx xx xx

   or similar kernel debugging information on your screen or in your
   system log, please duplicate it *exactly*.  The dump may look
   incomprehensible to you, but it does contain information that may
   help debugging the problem.  The text above the dump is also
   important: it tells something about why the kernel dumped code (in
   the above example, it's due to a bad kernel pointer). More information
   on making sense of the dump is in Documentation/oops-tracing.txt

 - If you compiled the kernel with CONFIG_KALLSYMS you can send the dump
   as is, otherwise you will have to use the "ksymoops" program to make
   sense of the dump (but compiling with CONFIG_KALLSYMS is usually preferred).
   This utility can be downloaded from
   ftp://ftp.<country>.kernel.org/pub/linux/utils/kernel/ksymoops/ .
   Alternatively, you can do the dump lookup by hand:

 - In debugging dumps like the above, it helps enormously if you can
   look up what the EIP value means.  The hex value as such doesn't help
   me or anybody else very much: it will depend on your particular
   kernel setup.  What you should do is take the hex value from the EIP
   line (ignore the "0010:"), and look it up in the kernel namelist to
   see which kernel function contains the offending address.

   To find out the kernel function name, you'll need to find the system
   binary associated with the kernel that exhibited the symptom.  This is
   the file 'linux/vmlinux'.  To extract the namelist and match it against
   the EIP from the kernel crash, do:

     nm vmlinux | sort | less

   This will give you a list of kernel addresses sorted in ascending
   order, from which it is simple to find the function that contains the
   offending address.  Note that the address given by the kernel
   debugging messages will not necessarily match exactly with the
   function addresses (in fact, that is very unlikely), so you can't
   just 'grep' the list: the list will, however, give you the starting
   point of each kernel function, so by looking for the function that
   has a starting address lower than the one you are searching for but
   is followed by a function with a higher address you will find the one
   you want.  In fact, it may be a good idea to include a bit of
   "context" in your problem report, giving a few lines around the
   interesting one.

   If you for some reason cannot do the above (you have a pre-compiled
   kernel image or similar), telling me as much about your setup as
   possible will help.  Please read the REPORTING-BUGS document for details.

 - Alternatively, you can use gdb on a running kernel. (read-only; i.e. you
   cannot change values or set break points.) To do this, first compile the
   kernel with -g; edit arch/x86/Makefile appropriately, then do a "make
   clean". You'll also need to enable CONFIG_PROC_FS (via "make config").

   After you've rebooted with the new kernel, do "gdb vmlinux /proc/kcore".
   You can now use all the usual gdb commands. The command to look up the
   point where your system crashed is "l *0xXXXXXXXX". (Replace the XXXes
   with the EIP value.)

   gdb'ing a non-running kernel currently fails because gdb (wrongly)
   disregards the starting offset for which the kernel is compiled.