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commit 2062afb4f804afef61cbe62a30cac9a46e58e067 upstream.
Michel Dänzer and a couple of other people reported inexplicable random
oopses in the scheduler, and the cause turns out to be gcc mis-compiling
the load_balance() function when debugging is enabled. The gcc bug
apparently goes back to gcc-4.5, but slight optimization changes means
that it now showed up as a problem in 4.9.0 and 4.9.1.
The instruction scheduling problem causes gcc to schedule a spill
operation to before the stack frame has been created, which in turn can
corrupt the spilled value if an interrupt comes in. There may be other
effects of this bug too, but that's the code generation problem seen in
Michel's case.
This is fixed in current gcc HEAD, but the workaround as suggested by
Markus Trippelsdorf is pretty simple: use -fno-var-tracking-assignments
when compiling the kernel, which disables the gcc code that causes the
problem. This can result in slightly worse debug information for
variable accesses, but that is infinitely preferable to actual code
generation problems.
Doing this unconditionally (not just for CONFIG_DEBUG_INFO) also allows
non-debug builds to verify that the debug build would be identical: we
can do
export GCC_COMPARE_DEBUG=1
to make gcc internally verify that the result of the build is
independent of the "-g" flag (it will make the compiler build everything
twice, toggling the debug flag, and compare the results).
Without the "-fno-var-tracking-assignments" option, the build would fail
(even with 4.8.3 that didn't show the actual stack frame bug) with a gcc
compare failure.
See also gcc bugzilla:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61801
Reported-by: Michel Dänzer <michel@daenzer.net>
Suggested-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Cc: Jakub Jelinek <jakub@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
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This reverts the Linux for Workgroups thing. And no, before somebody
asks, we're not doing Linux95. Not for a few years, at least.
Sure, the flag added some color to the logo, and could have remained as
a testament to my leet gimp skills. But no. And I'll do this early, to
avoid the chance of forgetting when I'm doing the actual rc1 release on
the road.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild
Pull kbuild update from Michal Marek:
"Only these two commits are in the kbuild branch this time:
- Using filechk for include/config/kernel.release
- Cleanup in scripts/sortextable.c"
* 'kbuild' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild:
kbuild: Do not overwrite include/config/kernel.release needlessly
scripts: remove unused function in sortextable.c
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Use filechk to detect if the content changed or not.
Signed-off-by: Michal Marek <mmarek@suse.cz>
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This reverts commit d2aae8477cd00325bb7c7c7e95be488088900c48.
It is completely and utterly broken. Module install should not build
any files, and adding broken dependencies to "help" it build files is
complete and utter sh*t.
The kernel should not be built by root, and "make install" and "make
module_install" (that for obvious reasons need to be run as root)
absolutely must not build any files. They should only ever copy the
already-built files over.
So having dependencies for the install targets is wrong, wrong, wrong.
If you try to install a kernel without building it first, you *should*
get errors. The build system shouldn't try to help root build the files.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild
Pull kbuild updates from Michal Marek:
- fix for make headers_install argv explosion with too long path
- scripts/setlocalversion does not call git update-index needlessly
- fix for the src.rpm produced by make rpm-pkg. The new make
image_name can be useful also for other packaging tools.
- scripts/mod/devicetable-offsets.o is not rebuilt during each make run
- make modules_install dependency fix
- scripts/sortextable portability fix
- fix for kbuild to generate the output directory for all object files
in subdirs.
- a couple of minor fixes
* 'kbuild' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild:
kbuild: create directory for dir/file.o
tools/include: use stdint types for user-space byteshift headers
Makefile: Fix install error with make -j option
Fix a build warning in scripts/mod/file2alias.c
improve modalias building
scripts/mod: Spelling s/DEVICEVTABLE/DEVICETABLE/
kbuild: fix error when building from src rpm
scripts/setlocalversion on write-protected source tree
Makefile.lib: align DTB quiet_cmd
kbuild: fix make headers_install when path is too long
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git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial
Pull trivial tree updates from Jiri Kosina:
"The usual stuff from trivial tree"
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial: (34 commits)
treewide: relase -> release
Documentation/cgroups/memory.txt: fix stat file documentation
sysctl/net.txt: delete reference to obsolete 2.4.x kernel
spinlock_api_smp.h: fix preprocessor comments
treewide: Fix typo in printk
doc: device tree: clarify stuff in usage-model.txt.
open firmware: "/aliasas" -> "/aliases"
md: bcache: Fixed a typo with the word 'arithmetic'
irq/generic-chip: fix a few kernel-doc entries
frv: Convert use of typedef ctl_table to struct ctl_table
sgi: xpc: Convert use of typedef ctl_table to struct ctl_table
doc: clk: Fix incorrect wording
Documentation/arm/IXP4xx fix a typo
Documentation/networking/ieee802154 fix a typo
Documentation/DocBook/media/v4l fix a typo
Documentation/video4linux/si476x.txt fix a typo
Documentation/virtual/kvm/api.txt fix a typo
Documentation/early-userspace/README fix a typo
Documentation/video4linux/soc-camera.txt fix a typo
lguest: fix CONFIG_PAE -> CONFIG_x86_PAE in comment
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