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Peter Zijlstra d136122f58 sched: Fix race against ptrace_freeze_trace() 
There is apparently one site that violates the rule that only current
and ttwu() will modify task->state, namely ptrace_{,un}freeze_traced()
will change task->state for a remote task.

Oleg explains:

  "TASK_TRACED/TASK_STOPPED was always protected by siglock. In
particular, ttwu(__TASK_TRACED) must be always called with siglock
held. That is why ptrace_freeze_traced() assumes it can safely do
s/TASK_TRACED/__TASK_TRACED/ under spin_lock(siglock)."

This breaks the ordering scheme introduced by commit:

  dbfb089d36 ("sched: Fix loadavg accounting race")

Specifically, the reload not matching no longer implies we don't have
to block.

Simply things by noting that what we need is a LOAD->STORE ordering
and this can be provided by a control dependency.

So replace:

	prev_state = prev->state;
	raw_spin_lock(&rq->lock);
	smp_mb__after_spinlock(); /* SMP-MB */
	if (... && prev_state && prev_state == prev->state)
		deactivate_task();

with:

	prev_state = prev->state;
	if (... && prev_state) /* CTRL-DEP */
		deactivate_task();

Since that already implies the 'prev->state' load must be complete
before allowing the 'prev->on_rq = 0' store to become visible.

Fixes: dbfb089d36 ("sched: Fix loadavg accounting race")
Reported-by: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Tested-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Tested-by: Christian Brauner <christian.brauner@ubuntu.com>
2020-07-22 10:22:00 +02:00
arch A pile of fixes for x86: 2020-07-19 12:16:09 -07:00
block block-5.8-2020-07-10 2020-07-10 09:55:46 -07:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto keys: asymmetric: fix error return code in software_key_query() 2020-07-15 15:49:04 -07:00
Documentation powerpc fixes for 5.8 #7 2020-07-18 10:45:17 -07:00
drivers Two fixes for the interrupt subsystem: 2020-07-19 11:53:08 -07:00
fs More NFS Client Bugfixes for Linux 5.8 2020-07-17 16:37:52 -07:00
include A set of scheduler fixes: 2020-07-19 11:55:24 -07:00
init kbuild: fix CONFIG_CC_CAN_LINK(_STATIC) for cross-compilation with Clang 2020-07-02 00:57:45 +09:00
ipc mmap locking API: use coccinelle to convert mmap_sem rwsem call sites 2020-06-09 09:39:14 -07:00
kernel sched: Fix race against ptrace_freeze_trace() 2020-07-22 10:22:00 +02:00
lib RISC-V Fixes for 5.8-rc5 (ideally) 2020-07-11 19:22:46 -07:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm mm: document warning in move_normal_pmd() and make it warn only once 2020-07-13 11:37:39 -07:00
net xprtrdma: fix incorrect header size calculations 2020-07-15 13:01:01 -04:00
samples samples/vfs: avoid warning in statx override 2020-07-03 16:15:25 -07:00
scripts kbuild: Move -Wtype-limits to W=2 2020-07-09 18:00:56 -07:00
security integrity/ima: switch to using __kernel_read 2020-07-08 08:27:57 +02:00
sound sound fixes for 5.8-rc6 2020-07-17 08:48:19 -07:00
tools Third batch of perf tooling fixes for 5.8: 2020-07-19 12:35:07 -07:00
usr bpfilter: match bit size of bpfilter_umh to that of the kernel 2020-05-17 18:52:01 +09:00
virt kvm: use more precise cast and do not drop __user 2020-07-02 05:39:31 -04:00
.clang-format block: add bio_for_each_bvec_all() 2020-05-25 11:25:24 +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: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: Do not track defconfig from make savedefconfig 2020-07-05 16:15:46 +09:00
.mailmap MAINTAINERS: update email address for Gerald Schaefer 2020-07-10 15:06:49 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS mailmap: change email for Ricardo Ribalda 2020-05-25 18:59:59 -06:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS regulator: Fixes for v5.8 2020-07-17 10:20:26 -07:00
Makefile Linux 5.8-rc6 2020-07-19 15:41:18 -07:00
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.