tree 8a33c3fb36e47fe4e79d4d0d23f2f14387271d69
parent b01b5ee9d80c79738056271e9d5722ce0dbb0a81
author Konstantin Khlebnikov <khlebnikov@yandex-team.ru> 1466081821 +0300
committer ChromeOS Commit Bot <chromeos-commit-bot@chromium.org> 1496695501 +0000

UPSTREAM: sched/fair: Initialize throttle_count for new task-groups lazily

Cgroup created inside throttled group must inherit current throttle_count.
Broken throttle_count allows to nominate throttled entries as a next buddy,
later this leads to null pointer dereference in pick_next_task_fair().

This patch initialize cfs_rq->throttle_count at first enqueue: laziness
allows to skip locking all rq at group creation. Lazy approach also allows
to skip full sub-tree scan at throttling hierarchy (not in this patch).

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bsegall@google.com
Link: http://lkml.kernel.org/r/146608182119.21870.8439834428248129633.stgit@buzz
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andrey Ulanov <andreyu@google.com>

(cherry-picked from commit 094f469172e00d6ab0a3130b0e01c83b3cf3a98d)

BUG=b:62255954
TEST=kernel compiles

Change-Id: I4b39f8ea3ff951fc59807b50c1bddde241c53efd
Reviewed-on: https://chromium-review.googlesource.com/521225
Commit-Ready: Andrey Ulanov <andreyu@google.com>
Tested-by: Andrey Ulanov <andreyu@google.com>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
(cherry picked from commit 43966ab2563e2df7cd0434350ee01d26ecaa615c)
Reviewed-on: https://chromium-review.googlesource.com/523026
Commit-Queue: Andrey Ulanov <andreyu@google.com>