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Ingo Molnar 7f682d7abc UPSTREAM: sched/core: Fix uclamp ABI bug, clean up and robustify sched_read_attr() ABI logic and code 
Thadeu Lima de Souza Cascardo reported that 'chrt' broke on recent kernels:

  $ chrt -p $$
  chrt: failed to get pid 26306's policy: Argument list too long

and he has root-caused the bug to the following commit increasing sched_attr
size and breaking sched_read_attr() into returning -EFBIG:

  a509a7cd79 ("sched/uclamp: Extend sched_setattr() to support utilization clamping")

The other, bigger bug is that the whole sched_getattr() and sched_read_attr()
logic of checking non-zero bits in new ABI components is arguably broken,
and pretty much any extension of the ABI will spuriously break the ABI.
That's way too fragile.

Instead implement the perf syscall's extensible ABI instead, which we
already implement on the sched_setattr() side:

 - if user-attributes have the same size as kernel attributes then the
   logic is unchanged.

 - if user-attributes are larger than the kernel knows about then simply
   skip the extra bits, but set attr->size to the (smaller) kernel size
   so that tooling can (in principle) handle older kernel as well.

 - if user-attributes are smaller than the kernel knows about then just
   copy whatever user-space can accept.

Also clean up the whole logic:

 - Simplify the code flow - there's no need for 'ret' for example.

 - Standardize on 'kattr/uattr' and 'ksize/usize' naming to make sure we
   always know which side we are dealing with.

 - Why is it called 'read' when what it does is to copy to user? This
   code is so far away from VFS read() semantics that the naming is
   actively confusing. Name it sched_attr_copy_to_user() instead, which
   mirrors other copy_to_user() functionality.

 - Move the attr->size assignment from the head of sched_getattr() to the
   sched_attr_copy_to_user() function. Nothing else within the kernel
   should care about the size of the structure.

With these fixes the sched_getattr() syscall now nicely supports an
extensible ABI in both a forward and backward compatible fashion, and
will also fix the chrt bug.

As an added bonus the bogus -EFBIG return is removed as well, which as
Thadeu noted should have been -E2BIG to begin with.

Bug: 120440300
Reported-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Tested-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Acked-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: a509a7cd79 ("sched/uclamp: Extend sched_setattr() to support utilization clamping")
Link: https://lkml.kernel.org/r/20190904075532.GA26751@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 1251201c0d)
Signed-off-by: Qais Yousef <qais.yousef@arm.com>
Change-Id: I67e653c4f69db0140e9651c125b60e2b8cfd62f1
Signed-off-by: Quentin Perret <qperret@google.com>
2020-02-01 15:03:15 +00:00
arch ANDROID: gki: Removed cf modules from gki_defconfig 2020-01-31 16:23:38 -08:00
block ANDROID: modularize BLK_MQ_VIRTIO 2020-01-31 16:11:59 -08:00
certs export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR() 2018-08-22 23:21:44 +09:00
crypto This is the 4.19.99 stable release 2020-01-27 15:55:44 +01:00
Documentation UPSTREAM: sched/uclamp: Extend CPU's cgroup controller 2020-02-01 15:03:14 +00:00
drivers ANDROID: Remove default y for VIRTIO_PCI_LEGACY 2020-01-31 16:12:00 -08:00
firmware Fix built-in early-load Intel microcode alignment 2020-01-23 08:21:29 +01:00
fs ANDROID: Incremental fs: Remove unneeded compatibility typedef 2020-01-30 13:53:08 -08:00
include UPSTREAM: sched/uclamp: Extend sched_setattr() to support utilization clamping 2020-02-01 14:39:37 +00:00
init UPSTREAM: sched/uclamp: Extend CPU's cgroup controller 2020-02-01 15:03:14 +00:00
ipc This is the 4.19.65 stable release 2019-08-06 20:08:18 +02:00
kernel UPSTREAM: sched/core: Fix uclamp ABI bug, clean up and robustify sched_read_attr() ABI logic and code 2020-02-01 15:03:15 +00:00
lib This is the 4.19.99 stable release 2020-01-27 15:55:44 +01:00
LICENSES LICENSES: Remove CC-BY-SA-4.0 license text 2018-10-18 11:28:50 +02:00
mm This is the 4.19.100 stable release 2020-01-29 17:10:45 +01:00
net This is the 4.19.100 stable release 2020-01-29 17:10:45 +01:00
samples samples/bpf: Fix broken xdp_rxq_info due to map order assumptions 2020-01-27 14:51:22 +01:00
scripts This is the 4.19.100 stable release 2020-01-29 17:10:45 +01:00
security This is the 4.19.99 stable release 2020-01-27 15:55:44 +01:00
sound This is the 4.19.99 stable release 2020-01-27 15:55:44 +01:00
tools ANDROID: Make incfs selftests pass 2020-01-30 11:25:57 -08:00
usr kbuild: clean compressed initramfs image 2019-10-07 18:57:16 +02:00
virt KVM: arm/arm64: vgic: Don't rely on the wrong pending table 2019-12-13 08:52:45 +01:00
.clang-format clang-format: Set IndentWrappedFunctionNames false 2018-08-01 18:38:51 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
abi_gki_aarch64_whitelist ANDROID: update ABI following inline crypto changes 2020-01-24 12:06:49 -08:00
abi_gki_aarch64.xml ANDROID: gki: Removed cf modules from gki_defconfig 2020-01-31 16:23:38 -08:00
build.config.aarch64 ANDROID: refactor build.config files to remove duplication 2019-10-22 18:27:12 -07:00
build.config.allmodconfig ANDROID: Don't base allmodconfig on gki_defconfig 2019-12-05 12:48:26 +00:00
build.config.allmodconfig.aarch64 ANDROID: Add allmodconfig build.configs for x86_64 and aarch64 2019-11-12 20:55:23 +00:00
build.config.allmodconfig.x86_64 ANDROID: Add allmodconfig build.configs for x86_64 and aarch64 2019-11-12 20:55:23 +00:00
build.config.common ANDROID: clang: update to 10.0.1 2019-11-27 12:37:18 -08:00
build.config.cuttlefish.aarch64 ANDROID: gki: Removed cf modules from gki_defconfig 2020-01-31 16:23:38 -08:00
build.config.cuttlefish.x86_64 ANDROID: gki: Removed cf modules from gki_defconfig 2020-01-31 16:23:38 -08:00
build.config.gki ANDROID: gki: Removed cf modules from gki_defconfig 2020-01-31 16:23:38 -08:00
build.config.gki.aarch64 ANDROID: add initial ABI whitelist for android-4.19 2019-12-18 12:44:33 +00:00
build.config.gki.x86_64 ANDROID: refactor build.config files to remove duplication 2019-10-22 18:27:12 -07:00
build.config.x86_64 ANDROID: refactor build.config files to remove duplication 2019-10-22 18:27:12 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS 9p: remove Ron Minnich from MAINTAINERS 2018-08-17 16:20:26 -07:00
cuttlefish.fragment ANDROID: gki: Removed cf modules from gki_defconfig 2020-01-31 16:23:38 -08:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS This is the 4.19.80 stable release 2019-10-17 15:33:07 -07:00
Makefile This is the 4.19.100 stable release 2020-01-29 17:10:45 +01:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -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.
See Documentation/00-INDEX for a list of what is contained in each file.

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.