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Masahiro Yamada ca2fc0dc1c ARC: build: move symlink creation to arch/arc/Makefile to avoid race
[ Upstream commit c5e6ae563c ]

If you run 'make uImage uImage.gz' with the parallel option, uImage.gz
will be created by two threads simultaneously.

This is because arch/arc/Makefile does not specify the dependency
between uImage and uImage.gz. Hence, GNU Make assumes they can be
built in parallel. One thread descends into arch/arc/boot/ to create
uImage, and another to create uImage.gz.

Please notice the same log is displayed twice in the following steps:

  $ export CROSS_COMPILE=<your-arc-compiler-prefix>
  $ make -s ARCH=arc defconfig
  $ make -j$(nproc) ARCH=arc uImage uImage.gz
  [ snip ]
    LD      vmlinux
    SORTTAB vmlinux
    SYSMAP  System.map
    OBJCOPY arch/arc/boot/vmlinux.bin
    OBJCOPY arch/arc/boot/vmlinux.bin
    GZIP    arch/arc/boot/vmlinux.bin.gz
    GZIP    arch/arc/boot/vmlinux.bin.gz
    UIMAGE  arch/arc/boot/uImage.gz
    UIMAGE  arch/arc/boot/uImage.gz
  Image Name:   Linux-5.10.0-rc4-00003-g62f23044
  Created:      Sun Nov 22 02:52:26 2020
  Image Type:   ARC Linux Kernel Image (gzip compressed)
  Data Size:    2109376 Bytes = 2059.94 KiB = 2.01 MiB
  Load Address: 80000000
  Entry Point:  80004000
    Image arch/arc/boot/uImage is ready
  Image Name:   Linux-5.10.0-rc4-00003-g62f23044
  Created:      Sun Nov 22 02:52:26 2020
  Image Type:   ARC Linux Kernel Image (gzip compressed)
  Data Size:    2815455 Bytes = 2749.47 KiB = 2.69 MiB
  Load Address: 80000000
  Entry Point:  80004000

This is a race between the two threads trying to write to the same file
arch/arc/boot/uImage.gz. This is a potential problem that can generate
a broken file.

I fixed a similar problem for ARM by commit 3939f33450 ("ARM: 8418/1:
add boot image dependencies to not generate invalid images").

I highly recommend to avoid such build rules that cause a race condition.

Move the uImage rule to arch/arc/Makefile.

Another strangeness is that arch/arc/boot/Makefile compares the
timestamps between $(obj)/uImage and $(obj)/uImage.*:

  $(obj)/uImage: $(obj)/uImage.$(suffix-y)
          @ln -sf $(notdir $<) $@
          @echo '  Image $@ is ready'

This does not work as expected since $(obj)/uImage is a symlink.
The symlink should be created in a phony target rule.

I used $(kecho) instead of echo to suppress the message
'Image arch/arc/boot/uImage is ready' when the -s option is given.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2021-01-19 18:26:14 +01:00
Documentation x86/CPU/AMD: Save AMD NodeId as cpu_die_id 2020-12-30 11:51:47 +01:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch ARC: build: move symlink creation to arch/arc/Makefile to avoid race 2021-01-19 18:26:14 +01:00
block block: fix use-after-free in disk_part_iter_next 2021-01-17 14:05:38 +01:00
certs PKCS#7: Refactor verify_pkcs7_signature() 2019-08-05 18:40:18 -04:00
crypto crypto: asym_tpm: correct zero out potential secrets 2021-01-12 20:16:17 +01:00
drivers dm integrity: fix flush with external metadata device 2021-01-19 18:26:13 +01:00
fs cifs: fix interrupted close commands 2021-01-19 18:26:13 +01:00
include dm integrity: fix flush with external metadata device 2021-01-19 18:26:13 +01:00
init exec: Transform exec_update_mutex into a rw_semaphore 2021-01-09 13:44:55 +01:00
ipc ipc/util.c: sysvipc_find_ipc() incorrectly updates position index 2020-05-20 08:20:16 +02:00
kernel tracing/kprobes: Do the notrace functions check without kprobes on ftrace 2021-01-19 18:26:12 +01:00
lib lib/genalloc: fix the overflow when size is too big 2021-01-12 20:16:10 +01:00
mm mm/hugetlb: fix potential missing huge page size info 2021-01-19 18:26:12 +01:00
net net: drop bogus skb with CHECKSUM_PARTIAL and offset beyond end of trimmed packet 2021-01-17 14:05:38 +01:00
samples samples: bpf: Fix lwt_len_hist reusing previous BPF map 2020-12-30 11:51:12 +01:00
scripts depmod: handle the case of /sbin/depmod without /sbin in PATH 2021-01-12 20:16:10 +01:00
security ima: Don't modify file descriptor mode on the fly 2020-12-30 11:51:39 +01:00
sound ASoC: dapm: remove widget from dirty list on free 2021-01-19 18:26:11 +01:00
tools bpftool: Fix compilation failure for net.o with older glibc 2021-01-17 14:05:37 +01:00
usr initramfs: restore default compression behavior 2020-04-08 09:08:38 +02:00
virt kvm: check tlbs_dirty directly 2021-01-12 20:16:22 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Modules updates for v5.4 2019-09-22 10:34:46 -07:00
.mailmap ARM: SoC fixes 2019-11-10 13:41:59 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS: Remove Simon as Renesas SoC Co-Maintainer 2019-10-10 08:12:51 -07:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS Documentation/llvm: add documentation on building w/ Clang/LLVM 2020-08-26 10:40:46 +02:00
Makefile kbuild: enforce -Werror=return-type 2021-01-19 18:26:11 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.