linux-stable.git/kernel/sched/core.c, branch v5.4.136 Linux kernel stable tree sched/uclamp: Fix uclamp_tg_restrict() 2021-07-14T14:53:24+00:00 Qais Yousef qais.yousef@arm.com 2021-06-17T16:51:55+00:00 97f32c7f3322780684930fb54400637c96c41bb4 [ Upstream commit 0213b7083e81f4acd69db32cb72eb4e5f220329a ] Now cpu.uclamp.min acts as a protection, we need to make sure that the uclamp request of the task is within the allowed range of the cgroup, that is it is clamp()'ed correctly by tg->uclamp[UCLAMP_MIN] and tg->uclamp[UCLAMP_MAX]. As reported by Xuewen [1] we can have some corner cases where there's inversion between uclamp requested by task (p) and the uclamp values of the taskgroup it's attached to (tg). Following table demonstrates 2 corner cases: | p | tg | effective -----------+-----+------+----------- CASE 1 -----------+-----+------+----------- uclamp_min | 60% | 0% | 60% -----------+-----+------+----------- uclamp_max | 80% | 50% | 50% -----------+-----+------+----------- CASE 2 -----------+-----+------+----------- uclamp_min | 0% | 30% | 30% -----------+-----+------+----------- uclamp_max | 20% | 50% | 20% -----------+-----+------+----------- With this fix we get: | p | tg | effective -----------+-----+------+----------- CASE 1 -----------+-----+------+----------- uclamp_min | 60% | 0% | 50% -----------+-----+------+----------- uclamp_max | 80% | 50% | 50% -----------+-----+------+----------- CASE 2 -----------+-----+------+----------- uclamp_min | 0% | 30% | 30% -----------+-----+------+----------- uclamp_max | 20% | 50% | 30% -----------+-----+------+----------- Additionally uclamp_update_active_tasks() must now unconditionally update both UCLAMP_MIN/MAX because changing the tg's UCLAMP_MAX for instance could have an impact on the effective UCLAMP_MIN of the tasks. | p | tg | effective -----------+-----+------+----------- old -----------+-----+------+----------- uclamp_min | 60% | 0% | 50% -----------+-----+------+----------- uclamp_max | 80% | 50% | 50% -----------+-----+------+----------- *new* -----------+-----+------+----------- uclamp_min | 60% | 0% | *60%* -----------+-----+------+----------- uclamp_max | 80% |*70%* | *70%* -----------+-----+------+----------- [1] https://lore.kernel.org/lkml/CAB8ipk_a6VFNjiEnHRHkUMBKbA+qzPQvhtNjJ_YNzQhqV_o8Zw@mail.gmail.com/ Fixes: 0c18f2ecfcc2 ("sched/uclamp: Fix wrong implementation of cpu.uclamp.min") Reported-by: Xuewen Yan <xuewen.yan94@gmail.com> Signed-off-by: Qais Yousef <qais.yousef@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20210617165155.3774110-1-qais.yousef@arm.com Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 0213b7083e81f4acd69db32cb72eb4e5f220329a ]

Now cpu.uclamp.min acts as a protection, we need to make sure that the
uclamp request of the task is within the allowed range of the cgroup,
that is it is clamp()'ed correctly by tg->uclamp[UCLAMP_MIN] and
tg->uclamp[UCLAMP_MAX].

As reported by Xuewen [1] we can have some corner cases where there's
inversion between uclamp requested by task (p) and the uclamp values of
the taskgroup it's attached to (tg). Following table demonstrates
2 corner cases:

	           |  p  |  tg  |  effective
	-----------+-----+------+-----------
	CASE 1
	-----------+-----+------+-----------
	uclamp_min | 60% | 0%   |  60%
	-----------+-----+------+-----------
	uclamp_max | 80% | 50%  |  50%
	-----------+-----+------+-----------
	CASE 2
	-----------+-----+------+-----------
	uclamp_min | 0%  | 30%  |  30%
	-----------+-----+------+-----------
	uclamp_max | 20% | 50%  |  20%
	-----------+-----+------+-----------

With this fix we get:

	           |  p  |  tg  |  effective
	-----------+-----+------+-----------
	CASE 1
	-----------+-----+------+-----------
	uclamp_min | 60% | 0%   |  50%
	-----------+-----+------+-----------
	uclamp_max | 80% | 50%  |  50%
	-----------+-----+------+-----------
	CASE 2
	-----------+-----+------+-----------
	uclamp_min | 0%  | 30%  |  30%
	-----------+-----+------+-----------
	uclamp_max | 20% | 50%  |  30%
	-----------+-----+------+-----------

Additionally uclamp_update_active_tasks() must now unconditionally
update both UCLAMP_MIN/MAX because changing the tg's UCLAMP_MAX for
instance could have an impact on the effective UCLAMP_MIN of the tasks.

	           |  p  |  tg  |  effective
	-----------+-----+------+-----------
	old
	-----------+-----+------+-----------
	uclamp_min | 60% | 0%   |  50%
	-----------+-----+------+-----------
	uclamp_max | 80% | 50%  |  50%
	-----------+-----+------+-----------
	*new*
	-----------+-----+------+-----------
	uclamp_min | 60% | 0%   | *60%*
	-----------+-----+------+-----------
	uclamp_max | 80% |*70%* | *70%*
	-----------+-----+------+-----------

[1] https://lore.kernel.org/lkml/CAB8ipk_a6VFNjiEnHRHkUMBKbA+qzPQvhtNjJ_YNzQhqV_o8Zw@mail.gmail.com/

Fixes: 0c18f2ecfcc2 ("sched/uclamp: Fix wrong implementation of cpu.uclamp.min")
Reported-by: Xuewen Yan <xuewen.yan94@gmail.com>
Signed-off-by: Qais Yousef <qais.yousef@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210617165155.3774110-1-qais.yousef@arm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
sched/uclamp: Fix locking around cpu_util_update_eff() 2021-07-14T14:53:20+00:00 Qais Yousef qais.yousef@arm.com 2021-05-10T14:50:32+00:00 8e5ffc103928414faed08e63ebbd61f1264cbc9b [ Upstream commit 93b73858701fd01de26a4a874eb95f9b7156fd4b ] cpu_cgroup_css_online() calls cpu_util_update_eff() without holding the uclamp_mutex or rcu_read_lock() like other call sites, which is a mistake. The uclamp_mutex is required to protect against concurrent reads and writes that could update the cgroup hierarchy. The rcu_read_lock() is required to traverse the cgroup data structures in cpu_util_update_eff(). Surround the caller with the required locks and add some asserts to better document the dependency in cpu_util_update_eff(). Fixes: 7226017ad37a ("sched/uclamp: Fix a bug in propagating uclamp value in new cgroups") Reported-by: Quentin Perret <qperret@google.com> Signed-off-by: Qais Yousef <qais.yousef@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20210510145032.1934078-3-qais.yousef@arm.com Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 93b73858701fd01de26a4a874eb95f9b7156fd4b ]

cpu_cgroup_css_online() calls cpu_util_update_eff() without holding the
uclamp_mutex or rcu_read_lock() like other call sites, which is
a mistake.

The uclamp_mutex is required to protect against concurrent reads and
writes that could update the cgroup hierarchy.

The rcu_read_lock() is required to traverse the cgroup data structures
in cpu_util_update_eff().

Surround the caller with the required locks and add some asserts to
better document the dependency in cpu_util_update_eff().

Fixes: 7226017ad37a ("sched/uclamp: Fix a bug in propagating uclamp value in new cgroups")
Reported-by: Quentin Perret <qperret@google.com>
Signed-off-by: Qais Yousef <qais.yousef@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210510145032.1934078-3-qais.yousef@arm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
sched/uclamp: Fix wrong implementation of cpu.uclamp.min 2021-07-14T14:53:20+00:00 Qais Yousef qais.yousef@arm.com 2021-05-10T14:50:31+00:00 0b199ce65bc34df1219f2d3f0ad7d25ee0be3732 [ Upstream commit 0c18f2ecfcc274a4bcc1d122f79ebd4001c3b445 ] cpu.uclamp.min is a protection as described in cgroup-v2 Resource Distribution Model Documentation/admin-guide/cgroup-v2.rst which means we try our best to preserve the minimum performance point of tasks in this group. See full description of cpu.uclamp.min in the cgroup-v2.rst. But the current implementation makes it a limit, which is not what was intended. For example: tg->cpu.uclamp.min = 20% p0->uclamp[UCLAMP_MIN] = 0 p1->uclamp[UCLAMP_MIN] = 50% Previous Behavior (limit): p0->effective_uclamp = 0 p1->effective_uclamp = 20% New Behavior (Protection): p0->effective_uclamp = 20% p1->effective_uclamp = 50% Which is inline with how protections should work. With this change the cgroup and per-task behaviors are the same, as expected. Additionally, we remove the confusing relationship between cgroup and !user_defined flag. We don't want for example RT tasks that are boosted by default to max to change their boost value when they attach to a cgroup. If a cgroup wants to limit the max performance point of tasks attached to it, then cpu.uclamp.max must be set accordingly. Or if they want to set different boost value based on cgroup, then sysctl_sched_util_clamp_min_rt_default must be used to NOT boost to max and set the right cpu.uclamp.min for each group to let the RT tasks obtain the desired boost value when attached to that group. As it stands the dependency on !user_defined flag adds an extra layer of complexity that is not required now cpu.uclamp.min behaves properly as a protection. The propagation model of effective cpu.uclamp.min in child cgroups as implemented by cpu_util_update_eff() is still correct. The parent protection sets an upper limit of what the child cgroups will effectively get. Fixes: 3eac870a3247 (sched/uclamp: Use TG's clamps to restrict TASK's clamps) Signed-off-by: Qais Yousef <qais.yousef@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20210510145032.1934078-2-qais.yousef@arm.com Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 0c18f2ecfcc274a4bcc1d122f79ebd4001c3b445 ]

cpu.uclamp.min is a protection as described in cgroup-v2 Resource
Distribution Model

	Documentation/admin-guide/cgroup-v2.rst

which means we try our best to preserve the minimum performance point of
tasks in this group. See full description of cpu.uclamp.min in the
cgroup-v2.rst.

But the current implementation makes it a limit, which is not what was
intended.

For example:

	tg->cpu.uclamp.min = 20%

	p0->uclamp[UCLAMP_MIN] = 0
	p1->uclamp[UCLAMP_MIN] = 50%

	Previous Behavior (limit):

		p0->effective_uclamp = 0
		p1->effective_uclamp = 20%

	New Behavior (Protection):

		p0->effective_uclamp = 20%
		p1->effective_uclamp = 50%

Which is inline with how protections should work.

With this change the cgroup and per-task behaviors are the same, as
expected.

Additionally, we remove the confusing relationship between cgroup and
!user_defined flag.

We don't want for example RT tasks that are boosted by default to max to
change their boost value when they attach to a cgroup. If a cgroup wants
to limit the max performance point of tasks attached to it, then
cpu.uclamp.max must be set accordingly.

Or if they want to set different boost value based on cgroup, then
sysctl_sched_util_clamp_min_rt_default must be used to NOT boost to max
and set the right cpu.uclamp.min for each group to let the RT tasks
obtain the desired boost value when attached to that group.

As it stands the dependency on !user_defined flag adds an extra layer of
complexity that is not required now cpu.uclamp.min behaves properly as
a protection.

The propagation model of effective cpu.uclamp.min in child cgroups as
implemented by cpu_util_update_eff() is still correct. The parent
protection sets an upper limit of what the child cgroups will
effectively get.

Fixes: 3eac870a3247 (sched/uclamp: Use TG's clamps to restrict TASK's clamps)
Signed-off-by: Qais Yousef <qais.yousef@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210510145032.1934078-2-qais.yousef@arm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
sched: Fix out-of-bound access in uclamp 2021-05-19T08:08:28+00:00 Quentin Perret qperret@google.com 2021-04-30T15:14:12+00:00 687f523c134b7f0bd040ee1230f6d17990d54172 [ Upstream commit 6d2f8909a5fabb73fe2a63918117943986c39b6c ] Util-clamp places tasks in different buckets based on their clamp values for performance reasons. However, the size of buckets is currently computed using a rounding division, which can lead to an off-by-one error in some configurations. For instance, with 20 buckets, the bucket size will be 1024/20=51. A task with a clamp of 1024 will be mapped to bucket id 1024/51=20. Sadly, correct indexes are in range [0,19], hence leading to an out of bound memory access. Clamp the bucket id to fix the issue. Fixes: 69842cba9ace ("sched/uclamp: Add CPU's clamp buckets refcounting") Suggested-by: Qais Yousef <qais.yousef@arm.com> Signed-off-by: Quentin Perret <qperret@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com> Link: https://lkml.kernel.org/r/20210430151412.160913-1-qperret@google.com Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 6d2f8909a5fabb73fe2a63918117943986c39b6c ]

Util-clamp places tasks in different buckets based on their clamp values
for performance reasons. However, the size of buckets is currently
computed using a rounding division, which can lead to an off-by-one
error in some configurations.

For instance, with 20 buckets, the bucket size will be 1024/20=51. A
task with a clamp of 1024 will be mapped to bucket id 1024/51=20. Sadly,
correct indexes are in range [0,19], hence leading to an out of bound
memory access.

Clamp the bucket id to fix the issue.

Fixes: 69842cba9ace ("sched/uclamp: Add CPU's clamp buckets refcounting")
Suggested-by: Qais Yousef <qais.yousef@arm.com>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lkml.kernel.org/r/20210430151412.160913-1-qperret@google.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
sched/features: Fix hrtick reprogramming 2021-03-07T11:20:47+00:00 Juri Lelli juri.lelli@redhat.com 2021-02-08T07:35:53+00:00 99d2926531ac2cfa95cb1b0ed9302c5e2c62be46 [ Upstream commit 156ec6f42b8d300dbbf382738ff35c8bad8f4c3a ] Hung tasks and RCU stall cases were reported on systems which were not 100% busy. Investigation of such unexpected cases (no sign of potential starvation caused by tasks hogging the system) pointed out that the periodic sched tick timer wasn't serviced anymore after a certain point and that caused all machinery that depends on it (timers, RCU, etc.) to stop working as well. This issues was however only reproducible if HRTICK was enabled. Looking at core dumps it was found that the rbtree of the hrtimer base used also for the hrtick was corrupted (i.e. next as seen from the base root and actual leftmost obtained by traversing the tree are different). Same base is also used for periodic tick hrtimer, which might get "lost" if the rbtree gets corrupted. Much alike what described in commit 1f71addd34f4c ("tick/sched: Do not mess with an enqueued hrtimer") there is a race window between hrtimer_set_expires() in hrtick_start and hrtimer_start_expires() in __hrtick_restart() in which the former might be operating on an already queued hrtick hrtimer, which might lead to corruption of the base. Use hrtick_start() (which removes the timer before enqueuing it back) to ensure hrtick hrtimer reprogramming is entirely guarded by the base lock, so that no race conditions can occur. Signed-off-by: Juri Lelli <juri.lelli@redhat.com> Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com> Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lkml.kernel.org/r/20210208073554.14629-2-juri.lelli@redhat.com Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 156ec6f42b8d300dbbf382738ff35c8bad8f4c3a ]

Hung tasks and RCU stall cases were reported on systems which were not
100% busy. Investigation of such unexpected cases (no sign of potential
starvation caused by tasks hogging the system) pointed out that the
periodic sched tick timer wasn't serviced anymore after a certain point
and that caused all machinery that depends on it (timers, RCU, etc.) to
stop working as well. This issues was however only reproducible if
HRTICK was enabled.

Looking at core dumps it was found that the rbtree of the hrtimer base
used also for the hrtick was corrupted (i.e. next as seen from the base
root and actual leftmost obtained by traversing the tree are different).
Same base is also used for periodic tick hrtimer, which might get "lost"
if the rbtree gets corrupted.

Much alike what described in commit 1f71addd34f4c ("tick/sched: Do not
mess with an enqueued hrtimer") there is a race window between
hrtimer_set_expires() in hrtick_start and hrtimer_start_expires() in
__hrtick_restart() in which the former might be operating on an already
queued hrtick hrtimer, which might lead to corruption of the base.

Use hrtick_start() (which removes the timer before enqueuing it back) to
ensure hrtick hrtimer reprogramming is entirely guarded by the base
lock, so that no race conditions can occur.

Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20210208073554.14629-2-juri.lelli@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
sched: Reenable interrupts in do_sched_yield() 2020-12-30T10:51:03+00:00 Thomas Gleixner tglx@linutronix.de 2020-10-20T14:46:55+00:00 52f525f2bdc78acecc4ae0997d2032e50934c1af [ Upstream commit 345a957fcc95630bf5535d7668a59ed983eb49a7 ] do_sched_yield() invokes schedule() with interrupts disabled which is not allowed. This goes back to the pre git era to commit a6efb709806c ("[PATCH] irqlock patch 2.5.27-H6") in the history tree. Reenable interrupts and remove the misleading comment which "explains" it. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/87r1pt7y5c.fsf@nanos.tec.linutronix.de Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 345a957fcc95630bf5535d7668a59ed983eb49a7 ]

do_sched_yield() invokes schedule() with interrupts disabled which is
not allowed. This goes back to the pre git era to commit a6efb709806c
("[PATCH] irqlock patch 2.5.27-H6") in the history tree.

Reenable interrupts and remove the misleading comment which "explains" it.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/87r1pt7y5c.fsf@nanos.tec.linutronix.de
Signed-off-by: Sasha Levin <sashal@kernel.org>
sched/features: Fix !CONFIG_JUMP_LABEL case 2020-10-29T08:58:00+00:00 Juri Lelli juri.lelli@redhat.com 2020-10-13T05:31:14+00:00 78e27678db4ea62377425df497c7421359888b1a [ Upstream commit a73f863af4ce9730795eab7097fb2102e6854365 ] Commit: 765cc3a4b224e ("sched/core: Optimize sched_feat() for !CONFIG_SCHED_DEBUG builds") made sched features static for !CONFIG_SCHED_DEBUG configurations, but overlooked the CONFIG_SCHED_DEBUG=y and !CONFIG_JUMP_LABEL cases. For the latter echoing changes to /sys/kernel/debug/sched_features has the nasty effect of effectively changing what sched_features reports, but without actually changing the scheduler behaviour (since different translation units get different sysctl_sched_features). Fix CONFIG_SCHED_DEBUG=y and !CONFIG_JUMP_LABEL configurations by properly restructuring ifdefs. Fixes: 765cc3a4b224e ("sched/core: Optimize sched_feat() for !CONFIG_SCHED_DEBUG builds") Co-developed-by: Daniel Bristot de Oliveira <bristot@redhat.com> Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com> Signed-off-by: Juri Lelli <juri.lelli@redhat.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Acked-by: Patrick Bellasi <patrick.bellasi@matbug.net> Reviewed-by: Valentin Schneider <valentin.schneider@arm.com> Link: https://lore.kernel.org/r/20201013053114.160628-1-juri.lelli@redhat.com Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit a73f863af4ce9730795eab7097fb2102e6854365 ]

Commit:

  765cc3a4b224e ("sched/core: Optimize sched_feat() for !CONFIG_SCHED_DEBUG builds")

made sched features static for !CONFIG_SCHED_DEBUG configurations, but
overlooked the CONFIG_SCHED_DEBUG=y and !CONFIG_JUMP_LABEL cases.

For the latter echoing changes to /sys/kernel/debug/sched_features has
the nasty effect of effectively changing what sched_features reports,
but without actually changing the scheduler behaviour (since different
translation units get different sysctl_sched_features).

Fix CONFIG_SCHED_DEBUG=y and !CONFIG_JUMP_LABEL configurations by properly
restructuring ifdefs.

Fixes: 765cc3a4b224e ("sched/core: Optimize sched_feat() for !CONFIG_SCHED_DEBUG builds")
Co-developed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Patrick Bellasi <patrick.bellasi@matbug.net>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Link: https://lore.kernel.org/r/20201013053114.160628-1-juri.lelli@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
workqueue: Remove the warning in wq_worker_sleeping() 2020-10-01T11:17:54+00:00 Sebastian Andrzej Siewior bigeasy@linutronix.de 2020-03-27T23:29:59+00:00 644148cd15378b89123e9cdc9d1840cf6135f7ea [ Upstream commit 62849a9612924a655c67cf6962920544aa5c20db ] The kernel test robot triggered a warning with the following race: task-ctx A interrupt-ctx B worker -> process_one_work() -> work_item() -> schedule(); -> sched_submit_work() -> wq_worker_sleeping() -> ->sleeping = 1 atomic_dec_and_test(nr_running) __schedule(); *interrupt* async_page_fault() -> local_irq_enable(); -> schedule(); -> sched_submit_work() -> wq_worker_sleeping() -> if (WARN_ON(->sleeping)) return -> __schedule() -> sched_update_worker() -> wq_worker_running() -> atomic_inc(nr_running); -> ->sleeping = 0; -> sched_update_worker() -> wq_worker_running() if (!->sleeping) return In this context the warning is pointless everything is fine. An interrupt before wq_worker_sleeping() will perform the ->sleeping assignment (0 -> 1 > 0) twice. An interrupt after wq_worker_sleeping() will trigger the warning and nr_running will be decremented (by A) and incremented once (only by B, A will skip it). This is the case until the ->sleeping is zeroed again in wq_worker_running(). Remove the WARN statement because this condition may happen. Document that preemption around wq_worker_sleeping() needs to be disabled to protect ->sleeping and not just as an optimisation. Fixes: 6d25be5782e48 ("sched/core, workqueues: Distangle worker accounting from rq lock") Reported-by: kernel test robot <lkp@intel.com> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: Tejun Heo <tj@kernel.org> Link: https://lkml.kernel.org/r/20200327074308.GY11705@shao2-debian Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 62849a9612924a655c67cf6962920544aa5c20db ]

The kernel test robot triggered a warning with the following race:
   task-ctx A                            interrupt-ctx B
 worker
  -> process_one_work()
    -> work_item()
      -> schedule();
         -> sched_submit_work()
           -> wq_worker_sleeping()
             -> ->sleeping = 1
               atomic_dec_and_test(nr_running)
         __schedule();                *interrupt*
                                       async_page_fault()
                                       -> local_irq_enable();
                                       -> schedule();
                                          -> sched_submit_work()
                                            -> wq_worker_sleeping()
                                               -> if (WARN_ON(->sleeping)) return
                                          -> __schedule()
                                            ->  sched_update_worker()
                                              -> wq_worker_running()
                                                 -> atomic_inc(nr_running);
                                                 -> ->sleeping = 0;

      ->  sched_update_worker()
        -> wq_worker_running()
          if (!->sleeping) return

In this context the warning is pointless everything is fine.
An interrupt before wq_worker_sleeping() will perform the ->sleeping
assignment (0 -> 1 > 0) twice.
An interrupt after wq_worker_sleeping() will trigger the warning and
nr_running will be decremented (by A) and incremented once (only by B, A
will skip it). This is the case until the ->sleeping is zeroed again in
wq_worker_running().

Remove the WARN statement because this condition may happen. Document
that preemption around wq_worker_sleeping() needs to be disabled to
protect ->sleeping and not just as an optimisation.

Fixes: 6d25be5782e48 ("sched/core, workqueues: Distangle worker accounting from rq lock")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Link: https://lkml.kernel.org/r/20200327074308.GY11705@shao2-debian
Signed-off-by: Sasha Levin <sashal@kernel.org>
sched/uclamp: Fix a deadlock when enabling uclamp static key 2020-09-03T09:26:49+00:00 Qais Yousef qais.yousef@arm.com 2020-08-28T12:56:10+00:00 2c0000f409ecea273b4adda594a2fabb44f3cc96 [ Upstream commit e65855a52b479f98674998cb23b21ef5a8144b04 ] The following splat was caught when setting uclamp value of a task: BUG: sleeping function called from invalid context at ./include/linux/percpu-rwsem.h:49 cpus_read_lock+0x68/0x130 static_key_enable+0x1c/0x38 __sched_setscheduler+0x900/0xad8 Fix by ensuring we enable the key outside of the critical section in __sched_setscheduler() Fixes: 46609ce22703 ("sched/uclamp: Protect uclamp fast path code with static key") Signed-off-by: Qais Yousef <qais.yousef@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20200716110347.19553-4-qais.yousef@arm.com Signed-off-by: Qais Yousef <qais.yousef@arm.com> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit e65855a52b479f98674998cb23b21ef5a8144b04 ]

The following splat was caught when setting uclamp value of a task:

  BUG: sleeping function called from invalid context at ./include/linux/percpu-rwsem.h:49

   cpus_read_lock+0x68/0x130
   static_key_enable+0x1c/0x38
   __sched_setscheduler+0x900/0xad8

Fix by ensuring we enable the key outside of the critical section in
__sched_setscheduler()

Fixes: 46609ce22703 ("sched/uclamp: Protect uclamp fast path code with static key")
Signed-off-by: Qais Yousef <qais.yousef@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200716110347.19553-4-qais.yousef@arm.com
Signed-off-by: Qais Yousef <qais.yousef@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
sched/uclamp: Protect uclamp fast path code with static key 2020-09-03T09:26:49+00:00 Qais Yousef qais.yousef@arm.com 2020-08-28T12:56:09+00:00 88435320ebc1df74e0af14ee04ca85423283fe7c [ Upstream commit 46609ce227039fd192e0ecc7d940bed587fd2c78 ] There is a report that when uclamp is enabled, a netperf UDP test regresses compared to a kernel compiled without uclamp. https://lore.kernel.org/lkml/20200529100806.GA3070@suse.de/ While investigating the root cause, there were no sign that the uclamp code is doing anything particularly expensive but could suffer from bad cache behavior under certain circumstances that are yet to be understood. https://lore.kernel.org/lkml/20200616110824.dgkkbyapn3io6wik@e107158-lin/ To reduce the pressure on the fast path anyway, add a static key that is by default will skip executing uclamp logic in the enqueue/dequeue_task() fast path until it's needed. As soon as the user start using util clamp by: 1. Changing uclamp value of a task with sched_setattr() 2. Modifying the default sysctl_sched_util_clamp_{min, max} 3. Modifying the default cpu.uclamp.{min, max} value in cgroup We flip the static key now that the user has opted to use util clamp. Effectively re-introducing uclamp logic in the enqueue/dequeue_task() fast path. It stays on from that point forward until the next reboot. This should help minimize the effect of util clamp on workloads that don't need it but still allow distros to ship their kernels with uclamp compiled in by default. SCHED_WARN_ON() in uclamp_rq_dec_id() was removed since now we can end up with unbalanced call to uclamp_rq_dec_id() if we flip the key while a task is running in the rq. Since we know it is harmless we just quietly return if we attempt a uclamp_rq_dec_id() when rq->uclamp[].bucket[].tasks is 0. In schedutil, we introduce a new uclamp_is_enabled() helper which takes the static key into account to ensure RT boosting behavior is retained. The following results demonstrates how this helps on 2 Sockets Xeon E5 2x10-Cores system. nouclamp uclamp uclamp-static-key Hmean send-64 162.43 ( 0.00%) 157.84 * -2.82%* 163.39 * 0.59%* Hmean send-128 324.71 ( 0.00%) 314.78 * -3.06%* 326.18 * 0.45%* Hmean send-256 641.55 ( 0.00%) 628.67 * -2.01%* 648.12 * 1.02%* Hmean send-1024 2525.28 ( 0.00%) 2448.26 * -3.05%* 2543.73 * 0.73%* Hmean send-2048 4836.14 ( 0.00%) 4712.08 * -2.57%* 4867.69 * 0.65%* Hmean send-3312 7540.83 ( 0.00%) 7425.45 * -1.53%* 7621.06 * 1.06%* Hmean send-4096 9124.53 ( 0.00%) 8948.82 * -1.93%* 9276.25 * 1.66%* Hmean send-8192 15589.67 ( 0.00%) 15486.35 * -0.66%* 15819.98 * 1.48%* Hmean send-16384 26386.47 ( 0.00%) 25752.25 * -2.40%* 26773.74 * 1.47%* The perf diff between nouclamp and uclamp-static-key when uclamp is disabled in the fast path: 8.73% -1.55% [kernel.kallsyms] [k] try_to_wake_up 0.07% +0.04% [kernel.kallsyms] [k] deactivate_task 0.13% -0.02% [kernel.kallsyms] [k] activate_task The diff between nouclamp and uclamp-static-key when uclamp is enabled in the fast path: 8.73% -0.72% [kernel.kallsyms] [k] try_to_wake_up 0.13% +0.39% [kernel.kallsyms] [k] activate_task 0.07% +0.38% [kernel.kallsyms] [k] deactivate_task Fixes: 69842cba9ace ("sched/uclamp: Add CPU's clamp buckets refcounting") Reported-by: Mel Gorman <mgorman@suse.de> Signed-off-by: Qais Yousef <qais.yousef@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Tested-by: Lukasz Luba <lukasz.luba@arm.com> Link: https://lkml.kernel.org/r/20200630112123.12076-3-qais.yousef@arm.com [ Fix minor conflict with kernel/sched.h because of function renamed later ] Signed-off-by: Qais Yousef <qais.yousef@arm.com> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 46609ce227039fd192e0ecc7d940bed587fd2c78 ]

There is a report that when uclamp is enabled, a netperf UDP test
regresses compared to a kernel compiled without uclamp.

https://lore.kernel.org/lkml/20200529100806.GA3070@suse.de/

While investigating the root cause, there were no sign that the uclamp
code is doing anything particularly expensive but could suffer from bad
cache behavior under certain circumstances that are yet to be
understood.

https://lore.kernel.org/lkml/20200616110824.dgkkbyapn3io6wik@e107158-lin/

To reduce the pressure on the fast path anyway, add a static key that is
by default will skip executing uclamp logic in the
enqueue/dequeue_task() fast path until it's needed.

As soon as the user start using util clamp by:

	1. Changing uclamp value of a task with sched_setattr()
	2. Modifying the default sysctl_sched_util_clamp_{min, max}
	3. Modifying the default cpu.uclamp.{min, max} value in cgroup

We flip the static key now that the user has opted to use util clamp.
Effectively re-introducing uclamp logic in the enqueue/dequeue_task()
fast path. It stays on from that point forward until the next reboot.

This should help minimize the effect of util clamp on workloads that
don't need it but still allow distros to ship their kernels with uclamp
compiled in by default.

SCHED_WARN_ON() in uclamp_rq_dec_id() was removed since now we can end
up with unbalanced call to uclamp_rq_dec_id() if we flip the key while
a task is running in the rq. Since we know it is harmless we just
quietly return if we attempt a uclamp_rq_dec_id() when
rq->uclamp[].bucket[].tasks is 0.

In schedutil, we introduce a new uclamp_is_enabled() helper which takes
the static key into account to ensure RT boosting behavior is retained.

The following results demonstrates how this helps on 2 Sockets Xeon E5
2x10-Cores system.

                                   nouclamp                 uclamp      uclamp-static-key
Hmean     send-64         162.43 (   0.00%)      157.84 *  -2.82%*      163.39 *   0.59%*
Hmean     send-128        324.71 (   0.00%)      314.78 *  -3.06%*      326.18 *   0.45%*
Hmean     send-256        641.55 (   0.00%)      628.67 *  -2.01%*      648.12 *   1.02%*
Hmean     send-1024      2525.28 (   0.00%)     2448.26 *  -3.05%*     2543.73 *   0.73%*
Hmean     send-2048      4836.14 (   0.00%)     4712.08 *  -2.57%*     4867.69 *   0.65%*
Hmean     send-3312      7540.83 (   0.00%)     7425.45 *  -1.53%*     7621.06 *   1.06%*
Hmean     send-4096      9124.53 (   0.00%)     8948.82 *  -1.93%*     9276.25 *   1.66%*
Hmean     send-8192     15589.67 (   0.00%)    15486.35 *  -0.66%*    15819.98 *   1.48%*
Hmean     send-16384    26386.47 (   0.00%)    25752.25 *  -2.40%*    26773.74 *   1.47%*

The perf diff between nouclamp and uclamp-static-key when uclamp is
disabled in the fast path:

     8.73%     -1.55%  [kernel.kallsyms]        [k] try_to_wake_up
     0.07%     +0.04%  [kernel.kallsyms]        [k] deactivate_task
     0.13%     -0.02%  [kernel.kallsyms]        [k] activate_task

The diff between nouclamp and uclamp-static-key when uclamp is enabled
in the fast path:

     8.73%     -0.72%  [kernel.kallsyms]        [k] try_to_wake_up
     0.13%     +0.39%  [kernel.kallsyms]        [k] activate_task
     0.07%     +0.38%  [kernel.kallsyms]        [k] deactivate_task

Fixes: 69842cba9ace ("sched/uclamp: Add CPU's clamp buckets refcounting")
Reported-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Qais Yousef <qais.yousef@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Lukasz Luba <lukasz.luba@arm.com>
Link: https://lkml.kernel.org/r/20200630112123.12076-3-qais.yousef@arm.com
[ Fix minor conflict with kernel/sched.h because of function renamed
later ]
Signed-off-by: Qais Yousef <qais.yousef@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>