kthread: add kthread_stop_put

Add a kthread_stop_put() helper that stops a thread and puts its task
struct. Use it to replace the various instances of kthread_stop()
followed by put_task_struct().

kthread: add kthread_stop_put

Add a kthread_stop_put() helper that stops a thread and puts its task
struct. Use it to replace the various instances of kthread_stop()
followed by put_task_struct().

Remove the kthread_stop_put() macro in usbip that is similar but doesn't
return the result of kthread_stop().

[[email protected]: fix kerneldoc comment]
Link: https://lkml.kernel.org/r/[email protected]
[[email protected]: document kthread_stop_put()'s argument]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Andreas Gruenbacher <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

show more ...

cpu/hotplug: Remove unused state functions

All users converted to the hotplug core mechanism.

Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infra

cpu/hotplug: Remove unused state functions

All users converted to the hotplug core mechanism.

Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Tested-by: Michael Kelley <[email protected]>
Tested-by: Oleksandr Natalenko <[email protected]>
Tested-by: Helge Deller <[email protected]> # parisc
Tested-by: Guilherme G. Piccoli <[email protected]> # Steam Deck
Link: https://lore.kernel.org/r/[email protected]

show more ...

cpu/hotplug: Remove cpu_report_state() and related unused cruft

No more users.

Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Teste

cpu/hotplug: Remove cpu_report_state() and related unused cruft

No more users.

Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Tested-by: Michael Kelley <[email protected]>
Tested-by: Oleksandr Natalenko <[email protected]>
Tested-by: Helge Deller <[email protected]> # parisc
Tested-by: Guilherme G. Piccoli <[email protected]> # Steam Deck
Link: https://lore.kernel.org/r/[email protected]

show more ...

cpu/hotplug: Add CPU state tracking and synchronization

The CPU state tracking and synchronization mechanism in smpboot.c is
completely independent of the hotplug code and all logic around it is
imp

cpu/hotplug: Add CPU state tracking and synchronization

The CPU state tracking and synchronization mechanism in smpboot.c is
completely independent of the hotplug code and all logic around it is
implemented in architecture specific code.

Except for the state reporting of the AP there is absolutely nothing
architecture specific and the sychronization and decision functions can be
moved into the generic hotplug core code.

Provide an integrated variant and add the core synchronization and decision
points. This comes in two flavours:

1) DEAD state synchronization

Updated by the architecture code once the AP reaches the point where
it is ready to be torn down by the control CPU, e.g. by removing power
or clocks or tear down via the hypervisor.

The control CPU waits for this state to be reached with a timeout. If
the state is reached an architecture specific cleanup function is
invoked.

2) Full state synchronization

This extends #1 with AP alive synchronization. This is new
functionality, which allows to replace architecture specific wait
mechanims, e.g. cpumasks, completely.

It also prevents that an AP which is in a limbo state can be brought
up again. This can happen when an AP failed to report dead state
during a previous off-line operation.

The dead synchronization is what most architectures use. Only x86 makes a
bringup decision based on that state at the moment.

Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Tested-by: Michael Kelley <[email protected]>
Tested-by: Oleksandr Natalenko <[email protected]>
Tested-by: Helge Deller <[email protected]> # parisc
Tested-by: Guilherme G. Piccoli <[email protected]> # Steam Deck
Link: https://lore.kernel.org/r/[email protected]

show more ...

smpboot: use atomic_try_cmpxchg in cpu_wait_death and cpu_report_death

Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) == old
in cpu_wait_death and cpu_report_death. x86 CMPXCHG i

smpboot: use atomic_try_cmpxchg in cpu_wait_death and cpu_report_death

Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) == old
in cpu_wait_death and cpu_report_death. x86 CMPXCHG instruction returns
success in ZF flag, so this change saves a compare after cmpxchg (and
related move instruction in front of cmpxchg). Also, atomic_try_cmpxchg
implicitly assigns old *ptr value to "old" when cmpxchg fails, enabling
further code simplifications.

No functional change intended.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Uros Bizjak <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

show more ...

cpu/hotplug: Allow the CPU in CPU_UP_PREPARE state to be brought up again.

A CPU will not show up in virtualized environment which includes an
Enclave. The VM splits its resources into a primary VM

cpu/hotplug: Allow the CPU in CPU_UP_PREPARE state to be brought up again.

A CPU will not show up in virtualized environment which includes an
Enclave. The VM splits its resources into a primary VM and a Enclave
VM. While the Enclave is active, the hypervisor will ignore all requests to
bring up a CPU and this CPU will remain in CPU_UP_PREPARE state.

The kernel will wait up to ten seconds for CPU to show up (do_boot_cpu())
and then rollback the hotplug state back to CPUHP_OFFLINE leaving the CPU
state in CPU_UP_PREPARE. The CPU state is set back to CPUHP_TEARDOWN_CPU
during the CPU_POST_DEAD stage.

After the Enclave VM terminates, the primary VM can bring up the CPU
again.

Allow to bring up the CPU if it is in the CPU_UP_PREPARE state.

[bigeasy: Rewrite commit description.]

Signed-off-by: Longpeng(Mike) <[email protected]>
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Tested-by: Dongli Zhang <[email protected]>
Reviewed-by: Valentin Schneider <[email protected]>
Reviewed-by: Henry Wang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

show more ...

smpboot: Replace deprecated CPU-hotplug functions.

The functions get_online_cpus() and put_online_cpus() have been
deprecated during the CPU hotplug rework. They map directly to
cpus_read_lock() and

smpboot: Replace deprecated CPU-hotplug functions.

The functions get_online_cpus() and put_online_cpus() have been
deprecated during the CPU hotplug rework. They map directly to
cpus_read_lock() and cpus_read_unlock().

Replace deprecated CPU-hotplug functions with the official version.
The behavior remains unchanged.

Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

show more ...

smpboot: fix duplicate and misplaced inlining directive

gcc doesn't care, but clang quite reasonably pointed out that the recent
commit e9ba16e68cce ("smpboot: Mark idle_init() as __always_inlined t

smpboot: fix duplicate and misplaced inlining directive

gcc doesn't care, but clang quite reasonably pointed out that the recent
commit e9ba16e68cce ("smpboot: Mark idle_init() as __always_inlined to
work around aggressive compiler un-inlining") did some really odd
things:

kernel/smpboot.c:50:20: warning: duplicate 'inline' declaration specifier [-Wduplicate-decl-specifier]
static inline void __always_inline idle_init(unsigned int cpu)
^

which not only has that duplicate inlining specifier, but the new
__always_inline was put in the wrong place of the function definition.

We put the storage class specifiers (ie things like "static" and
"extern") first, and the type information after that. And while the
compiler may not care, we put the inline specifier before the types.

So it should be just

static __always_inline void idle_init(unsigned int cpu)

instead.

Cc: Ingo Molnar <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

smpboot: Mark idle_init() as __always_inlined to work around aggressive compiler un-inlining

While this function is a static inline, and is only used once in
local scope, certain Kconfig variations

smpboot: Mark idle_init() as __always_inlined to work around aggressive compiler un-inlining

While this function is a static inline, and is only used once in
local scope, certain Kconfig variations may cause it to be compiled
as a standalone function:

89231bf0 <idle_init>:
89231bf0: 83 05 60 d9 45 89 01 addl $0x1,0x8945d960
89231bf7: 55 push %ebp

Resulting in this build failure:

WARNING: modpost: vmlinux.o(.text.unlikely+0x7fd5): Section mismatch in reference from the function idle_init() to the function .init.text:fork_idle()
The function idle_init() references
the function __init fork_idle().
This is often because idle_init lacks a __init
annotation or the annotation of fork_idle is wrong.
ERROR: modpost: Section mismatches detected.

Certain USBSAN options x86-32 builds with CONFIG_CC_OPTIMIZE_FOR_SIZE=y
seem to be causing this.

So mark idle_init() as __always_inline to work around this compiler
bug/feature.

Signed-off-by: Ingo Molnar <[email protected]>

show more ...

sched/core: Initialize the idle task with preemption disabled

As pointed out by commit

de9b8f5dcbd9 ("sched: Fix crash trying to dequeue/enqueue the idle thread")

init_idle() can and will be inv

sched/core: Initialize the idle task with preemption disabled

As pointed out by commit

de9b8f5dcbd9 ("sched: Fix crash trying to dequeue/enqueue the idle thread")

init_idle() can and will be invoked more than once on the same idle
task. At boot time, it is invoked for the boot CPU thread by
sched_init(). Then smp_init() creates the threads for all the secondary
CPUs and invokes init_idle() on them.

As the hotplug machinery brings the secondaries to life, it will issue
calls to idle_thread_get(), which itself invokes init_idle() yet again.
In this case it's invoked twice more per secondary: at _cpu_up(), and at
bringup_cpu().

Given smp_init() already initializes the idle tasks for all *possible*
CPUs, no further initialization should be required. Now, removing
init_idle() from idle_thread_get() exposes some interesting expectations
with regards to the idle task's preempt_count: the secondary startup always
issues a preempt_disable(), requiring some reset of the preempt count to 0
between hot-unplug and hotplug, which is currently served by
idle_thread_get() -> idle_init().

Given the idle task is supposed to have preemption disabled once and never
see it re-enabled, it seems that what we actually want is to initialize its
preempt_count to PREEMPT_DISABLED and leave it there. Do that, and remove
init_idle() from idle_thread_get().

Secondary startups were patched via coccinelle:

@begone@
@@

-preempt_disable();
...
cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);

Signed-off-by: Valentin Schneider <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

show more ...

kthread: Extract KTHREAD_IS_PER_CPU

There is a need to distinguish geniune per-cpu kthreads from kthreads
that happen to have a single CPU affinity.

Geniune per-cpu kthreads are kthreads that are C

kthread: Extract KTHREAD_IS_PER_CPU

There is a need to distinguish geniune per-cpu kthreads from kthreads
that happen to have a single CPU affinity.

Geniune per-cpu kthreads are kthreads that are CPU affine for
correctness, these will obviously have PF_KTHREAD set, but must also
have PF_NO_SETAFFINITY set, lest userspace modify their affinity and
ruins things.

However, these two things are not sufficient, PF_NO_SETAFFINITY is
also set on other tasks that have their affinities controlled through
other means, like for instance workqueues.

Therefore another bit is needed; it turns out kthread_create_per_cpu()
already has such a bit: KTHREAD_IS_PER_CPU, which is used to make
kthread_park()/kthread_unpark() work correctly.

Expose this flag and remove the implicit setting of it from
kthread_create_on_cpu(); the io_uring usage of it seems dubious at
best.

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Valentin Schneider <[email protected]>
Tested-by: Valentin Schneider <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

show more ...

treewide: Add SPDX license identifier for missed files

Add SPDX license identifiers to all files which:

- Have no license information of any form

- Have EXPORT_.*_SYMBOL_GPL inside which was use

treewide: Add SPDX license identifier for missed files

Add SPDX license identifiers to all files which:

- Have no license information of any form

- Have EXPORT_.*_SYMBOL_GPL inside which was used in the
initial scan/conversion to ignore the file

These files fall under the project license, GPL v2 only. The resulting SPDX
license identifier is:

GPL-2.0-only

Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

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smpboot: Remove cpumask from the API

Now that the sole use of the whole smpboot_*cpumask() API is gone,
remove it.

Suggested-by: Oleg Nesterov <[email protected]>
Signed-off-by: Peter Zijlstra (Intel

smpboot: Remove cpumask from the API

Now that the sole use of the whole smpboot_*cpumask() API is gone,
remove it.

Suggested-by: Oleg Nesterov <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Signed-off-by: Ingo Molnar <[email protected]>

show more ...

watchdog/core, powerpc: Lock cpus across reconfiguration

Instead of dropping the cpu hotplug lock after stopping NMI watchdog and
threads and reaquiring for restart, the code and the protection rule

watchdog/core, powerpc: Lock cpus across reconfiguration

Instead of dropping the cpu hotplug lock after stopping NMI watchdog and
threads and reaquiring for restart, the code and the protection rules
become more obvious when holding cpu hotplug lock across the full
reconfiguration.

Suggested-by: Linus Torvalds <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Acked-by: Michael Ellerman <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Don Zickus <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1710022105570.2114@nanos

show more ...

smpboot/threads, watchdog/core: Avoid runtime allocation

smpboot_update_cpumask_threads_percpu() allocates a temporary cpumask at
runtime. This is suboptimal because the call site needs more code si

smpboot/threads, watchdog/core: Avoid runtime allocation

smpboot_update_cpumask_threads_percpu() allocates a temporary cpumask at
runtime. This is suboptimal because the call site needs more code size for
proper error handling than a statically allocated temporary mask requires
data size.

Add static temporary cpumask. The function is globaly serialized, so no
further protection required.

Remove the half baken error handling in the watchdog code and get rid of
the export as there are no in tree modular users of that function.

Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Don Zickus <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Chris Metcalf <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Sebastian Siewior <[email protected]>
Cc: Ulrich Obergfell <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

show more ...

sched/headers: Prepare for new header dependencies before moving code to <linux/sched/task.h>

We are going to split <linux/sched/task.h> out of <linux/sched.h>, which
will have to be picked up from

sched/headers: Prepare for new header dependencies before moving code to <linux/sched/task.h>

We are going to split <linux/sched/task.h> out of <linux/sched.h>, which
will have to be picked up from other headers and a couple of .c files.

Create a trivial placeholder <linux/sched/task.h> file that just
maps to <linux/sched.h> to make this patch obviously correct and
bisectable.

Include the new header in the files that are going to need it.

Acked-by: Linus Torvalds <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Signed-off-by: Ingo Molnar <[email protected]>

show more ...

kthread/smpboot: do not park in kthread_create_on_cpu()

kthread_create_on_cpu() was added by the commit 2a1d446019f9a5983e
("kthread: Implement park/unpark facility"). It is currently used only
whe

kthread/smpboot: do not park in kthread_create_on_cpu()

kthread_create_on_cpu() was added by the commit 2a1d446019f9a5983e
("kthread: Implement park/unpark facility"). It is currently used only
when enabling new CPU. For this purpose, the newly created kthread has to
be parked.

The CPU binding is a bit tricky. The kthread is parked when the CPU has
not been allowed yet. And the CPU is bound when the kthread is unparked.

The function would be useful for more per-CPU kthreads, e.g.
bnx2fc_thread, fcoethread. For this purpose, the newly created kthread
should stay in the uninterruptible state.

This patch moves the parking into smpboot. It binds the thread already
when created. Then the function might be used universally. Also the
behavior is consistent with kthread_create() and kthread_create_on_node().

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>
Reviewed-by: Thomas Gleixner <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>
Cc: Josh Triplett <[email protected]>
Cc: Jiri Kosina <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

Revert "sched/core: Do not use smp_processor_id() with preempt enabled in smpboot_thread_fn()"

This reverts commit 4fa5cd5245b627db88c9ca08ae442373b02596b4.

The original change widens a preempt-off

Revert "sched/core: Do not use smp_processor_id() with preempt enabled in smpboot_thread_fn()"

This reverts commit 4fa5cd5245b627db88c9ca08ae442373b02596b4.

The original change widens a preempt-off section, to avoid a seemingly unsafe
smp_processor_id() use.

During review I overlooked two facts:

- The code to calls a non-trivial function callback:

ht->park(td->cpu);

... which might (and does occasionally) sleep, triggering the warning.

- More importantly, as pointed out by Peter Zijlstra, using
smp_processor_id() in that context is safe, if it's done from
a kernel thread that is pinned to a single CPU - which is the
case here.

So revert to the original code that enables preemption sooner.

Reported-by: kernel test robot <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Cc: Con Kolivas <[email protected]>
Cc: Alfred Chen <[email protected]>
Link: http://lkml.kernel.org/r/20160930015102.GB20189@yexl-desktop
Signed-off-by: Ingo Molnar <[email protected]>

show more ...

sched/core: Do not use smp_processor_id() with preempt enabled in smpboot_thread_fn()

We should not be using smp_processor_id() with preempt enabled.

Bug identified and fix provided by Alfred Chen.

sched/core: Do not use smp_processor_id() with preempt enabled in smpboot_thread_fn()

We should not be using smp_processor_id() with preempt enabled.

Bug identified and fix provided by Alfred Chen.

Reported-by: Alfred Chen <[email protected]>
Signed-off-by: Con Kolivas <[email protected]>
Cc: Alfred Chen <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/2042051.3vvUWIM0vs@hex
Signed-off-by: Ingo Molnar <[email protected]>

show more ...

cpu/hotplug: Unpark smpboot threads from the state machine

Handle the smpboot threads in the state machine.

Signed-off-by: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: Ri

cpu/hotplug: Unpark smpboot threads from the state machine

Handle the smpboot threads in the state machine.

Signed-off-by: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: Rik van Riel <[email protected]>
Cc: Rafael Wysocki <[email protected]>
Cc: "Srivatsa S. Bhat" <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Arjan van de Ven <[email protected]>
Cc: Sebastian Siewior <[email protected]>
Cc: Rusty Russell <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Paul McKenney <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul Turner <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Thomas Gleixner <[email protected]>

show more ...

stop_machine: Kill smp_hotplug_thread->pre_unpark, introduce stop_machine_unpark()

1. Change smpboot_unpark_thread() to check ->selfparking, just
like smpboot_park_thread() does.

2. Introduce st

stop_machine: Kill smp_hotplug_thread->pre_unpark, introduce stop_machine_unpark()

1. Change smpboot_unpark_thread() to check ->selfparking, just
like smpboot_park_thread() does.

2. Introduce stop_machine_unpark() which sets ->enabled and calls
kthread_unpark().

3. Change smpboot_thread_call() and cpu_stop_init() to call
stop_machine_unpark() by hand.

This way:

- IMO the ->selfparking logic becomes more consistent.

- We can kill the smp_hotplug_thread->pre_unpark() method.

- We can easily unpark the stopper thread earlier. Say, we
can move stop_machine_unpark() from smpboot_thread_call()
to sched_cpu_active() as Peter suggests.

Signed-off-by: Oleg Nesterov <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

show more ...

smpboot: allow passing the cpumask on per-cpu thread registration

It makes the registration cheaper and simpler for the smpboot per-cpu
kthread users that don't need to always update the cpumask aft

smpboot: allow passing the cpumask on per-cpu thread registration

It makes the registration cheaper and simpler for the smpboot per-cpu
kthread users that don't need to always update the cpumask after threads
creation.

[[email protected]: fix for allow passing the cpumask on per-cpu thread registration]
Signed-off-by: Frederic Weisbecker <[email protected]>
Reviewed-by: Chris Metcalf <[email protected]>
Reviewed-by: Thomas Gleixner <[email protected]>
Cc: Chris Metcalf <[email protected]>
Cc: Don Zickus <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ulrich Obergfell <[email protected]>
Signed-off-by: Stephen Rothwell <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

smpboot: make cleanup to mirror setup

The per-cpu kthread cleanup() callback is the mirror of the setup()
callback. When the per-cpu kthread is started, it first calls setup()
to initialize the res

smpboot: make cleanup to mirror setup

The per-cpu kthread cleanup() callback is the mirror of the setup()
callback. When the per-cpu kthread is started, it first calls setup()
to initialize the resources which are then released by cleanup() when
the kthread exits.

Now since the introduction of a per-cpu kthread cpumask, the kthreads
excluded by the cpumask on boot may happen to be parked immediately
after their creation without taking the setup() stage, waiting to be
asked to unpark to do so. Then when smpboot_unregister_percpu_thread()
is later called, the kthread is stopped without having ever called
setup().

But this triggers a bug as the kthread unconditionally calls cleanup()
on exit but this doesn't mirror any setup(). Thus the kernel crashes
because we try to free resources that haven't been initialized, as in
the watchdog case:

WATCHDOG disable 0
WATCHDOG disable 1
WATCHDOG disable 2
BUG: unable to handle kernel NULL pointer dereference at (null)
IP: hrtimer_active+0x26/0x60
[...]
Call Trace:
hrtimer_try_to_cancel+0x1c/0x280
hrtimer_cancel+0x1d/0x30
watchdog_disable+0x56/0x70
watchdog_cleanup+0xe/0x10
smpboot_thread_fn+0x23c/0x2c0
kthread+0xf8/0x110
ret_from_fork+0x3f/0x70

This bug is currently masked with explicit kthread unparking before
kthread_stop() on smpboot_destroy_threads(). This forces a call to
setup() and then unpark().

We could fix this by unconditionally calling setup() on kthread entry.
But setup() isn't always cheap. In the case of watchdog it launches
hrtimer, perf events, etc... So we may as well like to skip it if there
are chances the kthread will never be used, as in a reduced cpumask value.

So let's simply do a state machine check before calling cleanup() that
makes sure setup() has been called before mirroring it.

And remove the nasty hack workaround.

Signed-off-by: Frederic Weisbecker <[email protected]>
Reviewed-by: Chris Metcalf <[email protected]>
Reviewed-by: Thomas Gleixner <[email protected]>
Cc: Chris Metcalf <[email protected]>
Cc: Don Zickus <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ulrich Obergfell <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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smpboot: fix memory leak on error handling

The cpumask is allocated before threads get created. If the latter step
fails, we need to free the cpumask.

Signed-off-by: Frederic Weisbecker <fweisbec@g

smpboot: fix memory leak on error handling

The cpumask is allocated before threads get created. If the latter step
fails, we need to free the cpumask.

Signed-off-by: Frederic Weisbecker <[email protected]>
Reviewed-by: Chris Metcalf <[email protected]>
Reviewed-by: Thomas Gleixner <[email protected]>
Cc: Chris Metcalf <[email protected]>
Cc: Don Zickus <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ulrich Obergfell <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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watchdog: add watchdog_cpumask sysctl to assist nohz

Change the default behavior of watchdog so it only runs on the
housekeeping cores when nohz_full is enabled at build and boot time.
Allow modifyi

watchdog: add watchdog_cpumask sysctl to assist nohz

Change the default behavior of watchdog so it only runs on the
housekeeping cores when nohz_full is enabled at build and boot time.
Allow modifying the set of cores the watchdog is currently running on
with a new kernel.watchdog_cpumask sysctl.

In the current system, the watchdog subsystem runs a periodic timer that
schedules the watchdog kthread to run. However, nohz_full cores are
designed to allow userspace application code running on those cores to
have 100% access to the CPU. So the watchdog system prevents the
nohz_full application code from being able to run the way it wants to,
thus the motivation to suppress the watchdog on nohz_full cores, which
this patchset provides by default.

However, if we disable the watchdog globally, then the housekeeping
cores can't benefit from the watchdog functionality. So we allow
disabling it only on some cores. See Documentation/lockup-watchdogs.txt
for more information.

[[email protected]: fix a watchdog crash in some configurations]
Signed-off-by: Chris Metcalf <[email protected]>
Acked-by: Don Zickus <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Ulrich Obergfell <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Signed-off-by: John Hubbard <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...