linux.git/kernel/cpu.c, branch v5.15.114

cpu/hotplug: Do not bail-out in DYING/STARTING sections

2022-12-31T12:14:04+00:00

[ Upstream commit 6f855b39e4602b6b42a8e5cbcfefb8a1b8b5f0be ]

The DYING/STARTING callbacks are not expected to fail. However, as reported
by Derek, buggy drivers such as tboot are still free to return errors
within those sections, which halts the hot(un)plug and leaves the CPU in an
unrecoverable state.

As there is no rollback possible, only log the failures and proceed with
the following steps.

This restores the hotplug behaviour prior to commit 453e41085183
("cpu/hotplug: Add cpuhp_invoke_callback_range()")

Fixes: 453e41085183 ("cpu/hotplug: Add cpuhp_invoke_callback_range()")
Reported-by: Derek Dolney 
Signed-off-by: Vincent Donnefort 
Signed-off-by: Thomas Gleixner 
Tested-by: Derek Dolney 
Reviewed-by: Valentin Schneider 
Link: https://bugzilla.kernel.org/show_bug.cgi?id=215867
Link: https://lore.kernel.org/r/20220927101259.1149636-1-vdonnefort@google.com
Signed-off-by: Sasha Levin

cpu/hotplug: Make target_store() a nop when target == state

2022-12-31T12:14:04+00:00

[ Upstream commit 64ea6e44f85b9b75925ebe1ba0e6e8430cc4e06f ]

Writing the current state back in hotplug/target calls cpu_down()
which will set cpu dying even when it isn't and then nothing will
ever clear it. A stress test that reads values and writes them back
for all cpu device files in sysfs will trigger the BUG() in
select_fallback_rq once all cpus are marked as dying.

kernel/cpu.c::target_store()
	...
        if (st->state < target)
                ret = cpu_up(dev->id, target);
        else
                ret = cpu_down(dev->id, target);

cpu_down() -> cpu_set_state()
	 bool bringup = st->state < target;
	 ...
	 if (cpu_dying(cpu) != !bringup)
		set_cpu_dying(cpu, !bringup);

Fix this by letting state==target fall through in the target_store()
conditional. Also make sure st->target == target in that case.

Fixes: 757c989b9994 ("cpu/hotplug: Make target state writeable")
Signed-off-by: Phil Auld 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Valentin Schneider 
Link: https://lore.kernel.org/r/20221117162329.3164999-2-pauld@redhat.com
Signed-off-by: Sasha Levin

random: clear fast pool, crng, and batches in cpuhp bring up

2022-05-30T07:29:09+00:00

commit 3191dd5a1179ef0fad5a050a1702ae98b6251e8f upstream.

For the irq randomness fast pool, rather than having to use expensive
atomics, which were visibly the most expensive thing in the entire irq
handler, simply take care of the extreme edge case of resetting count to
zero in the cpuhp online handler, just after workqueues have been
reenabled. This simplifies the code a bit and lets us use vanilla
variables rather than atomics, and performance should be improved.

As well, very early on when the CPU comes up, while interrupts are still
disabled, we clear out the per-cpu crng and its batches, so that it
always starts with fresh randomness.

Cc: Thomas Gleixner 
Cc: Peter Zijlstra 
Cc: Theodore Ts'o 
Cc: Sultan Alsawaf 
Cc: Dominik Brodowski 
Acked-by: Sebastian Andrzej Siewior 
Signed-off-by: Jason A. Donenfeld 
Signed-off-by: Greg Kroah-Hartman

cpu/hotplug: Remove the 'cpu' member of cpuhp_cpu_state

2022-04-20T07:34:21+00:00

commit b7ba6d8dc3569e49800ef0136799f26f43e237e8 upstream.

Currently the setting of the 'cpu' member of struct cpuhp_cpu_state in
cpuhp_create() is too late as it is used earlier in _cpu_up().

If kzalloc_node() in __smpboot_create_thread() fails then the rollback will
be done with st->cpu==0 causing CPU0 to be erroneously set to be dying,
causing the scheduler to get mightily confused and throw its toys out of
the pram.

However the cpu number is actually available directly, so simply remove
the 'cpu' member and avoid the problem in the first place.

Fixes: 2ea46c6fc945 ("cpumask/hotplug: Fix cpu_dying() state tracking")
Signed-off-by: Steven Price 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20220411152233.474129-2-steven.price@arm.com
Signed-off-by: Greg Kroah-Hartman

sched/scs: Reset task stack state in bringup_cpu()

2021-12-01T08:04:54+00:00

[ Upstream commit dce1ca0525bfdc8a69a9343bc714fbc19a2f04b3 ]

To hot unplug a CPU, the idle task on that CPU calls a few layers of C
code before finally leaving the kernel. When KASAN is in use, poisoned
shadow is left around for each of the active stack frames, and when
shadow call stacks are in use. When shadow call stacks (SCS) are in use
the task's saved SCS SP is left pointing at an arbitrary point within
the task's shadow call stack.

When a CPU is offlined than onlined back into the kernel, this stale
state can adversely affect execution. Stale KASAN shadow can alias new
stackframes and result in bogus KASAN warnings. A stale SCS SP is
effectively a memory leak, and prevents a portion of the shadow call
stack being used. Across a number of hotplug cycles the idle task's
entire shadow call stack can become unusable.

We previously fixed the KASAN issue in commit:

  e1b77c92981a5222 ("sched/kasan: remove stale KASAN poison after hotplug")

... by removing any stale KASAN stack poison immediately prior to
onlining a CPU.

Subsequently in commit:

  f1a0a376ca0c4ef1 ("sched/core: Initialize the idle task with preemption disabled")

... the refactoring left the KASAN and SCS cleanup in one-time idle
thread initialization code rather than something invoked prior to each
CPU being onlined, breaking both as above.

We fixed SCS (but not KASAN) in commit:

  63acd42c0d4942f7 ("sched/scs: Reset the shadow stack when idle_task_exit")

... but as this runs in the context of the idle task being offlined it's
potentially fragile.

To fix these consistently and more robustly, reset the SCS SP and KASAN
shadow of a CPU's idle task immediately before we online that CPU in
bringup_cpu(). This ensures the idle task always has a consistent state
when it is running, and removes the need to so so when exiting an idle
task.

Whenever any thread is created, dup_task_struct() will give the task a
stack which is free of KASAN shadow, and initialize the task's SCS SP,
so there's no need to specially initialize either for idle thread within
init_idle(), as this was only necessary to handle hotplug cycles.

I've tested this on arm64 with:

* gcc 11.1.0, defconfig +KASAN_INLINE, KASAN_STACK
* clang 12.0.0, defconfig +KASAN_INLINE, KASAN_STACK, SHADOW_CALL_STACK

... offlining and onlining CPUS with:

| while true; do
|   for C in /sys/devices/system/cpu/cpu*/online; do
|     echo 0 > $C;
|     echo 1 > $C;
|   done
| done

Fixes: f1a0a376ca0c4ef1 ("sched/core: Initialize the idle task with preemption disabled")
Reported-by: Qian Cai 
Signed-off-by: Mark Rutland 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Valentin Schneider 
Tested-by: Qian Cai 
Link: https://lore.kernel.org/lkml/20211115113310.35693-1-mark.rutland@arm.com/
Signed-off-by: Sasha Levin

cpu/hotplug: Add debug printks for hotplug callback failures

2021-08-10T16:31:32+00:00

CPU hotplug callbacks can fail and cause a rollback to the previous
state. These failures are silent and therefore hard to debug.

Add pr_debug() to the up and down paths which provide information about the
error code, the CPU and the failed state. The debug printks can be enabled
via kernel command line or sysfs.

[ tglx: Adopt to current mainline, massage printk and changelog ]

Signed-off-by: Dongli Zhang 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Qais Yousef 
Link: https://lore.kernel.org/r/20210409055316.1709-1-dongli.zhang@oracle.com

cpu/hotplug: Use DEVICE_ATTR_*() macro

2021-08-10T16:11:12+00:00

Use DEVICE_ATTR_*() helper instead of plain DEVICE_ATTR,
which makes the code a bit shorter and easier to read.

Signed-off-by: YueHaibing 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20210527141105.2312-1-yuehaibing@huawei.com

cpu/hotplug: Eliminate all kernel-doc warnings

2021-08-10T16:07:38+00:00

kernel/cpu.c:57: warning: cannot understand function prototype: 'struct cpuhp_cpu_state '
kernel/cpu.c:115: warning: cannot understand function prototype: 'struct cpuhp_step '
kernel/cpu.c:146: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * cpuhp_invoke_callback _ Invoke the callbacks for a given state
kernel/cpu.c:75: warning: Function parameter or member 'fail' not described in 'cpuhp_cpu_state'
kernel/cpu.c:75: warning: Function parameter or member 'cpu' not described in 'cpuhp_cpu_state'
kernel/cpu.c:75: warning: Function parameter or member 'node' not described in 'cpuhp_cpu_state'
kernel/cpu.c:75: warning: Function parameter or member 'last' not described in 'cpuhp_cpu_state'
kernel/cpu.c:130: warning: Function parameter or member 'list' not described in 'cpuhp_step'
kernel/cpu.c:130: warning: Function parameter or member 'multi_instance' not described in 'cpuhp_step'
kernel/cpu.c:158: warning: No description found for return value of 'cpuhp_invoke_callback'
kernel/cpu.c:1188: warning: No description found for return value of 'cpu_device_down'
kernel/cpu.c:1400: warning: No description found for return value of 'cpu_device_up'
kernel/cpu.c:1425: warning: No description found for return value of 'bringup_hibernate_cpu'

Signed-off-by: Randy Dunlap 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20210809223825.24512-1-rdunlap@infradead.org

cpu/hotplug: Fix kernel doc warnings for __cpuhp_setup_state_cpuslocked()

2021-08-10T16:07:38+00:00

Fixes the following W=1 kernel build warning(s):

 kernel/cpu.c:1949: warning: Function parameter or member 
  'name' not described in '__cpuhp_setup_state_cpuslocked'

Signed-off-by: Baokun Li 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20210605063003.681049-1-libaokun1@huawei.com

Merge tag 'smp-urgent-2021-06-29' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2021-06-29T19:23:02+00:00

Pull CPU hotplug fix from Thomas Gleixner:
 "A fix for the CPU hotplug and cpusets interaction:

  cpusets delegate the hotplug work to a workqueue to prevent a lock
  order inversion vs. the CPU hotplug lock. The work is not flushed
  before the hotplug operation returns which creates user visible
  inconsistent state. Prevent this by flushing the work after dropping
  CPU hotplug lock and before releasing the outer mutex which serializes
  the CPU hotplug related sysfs interface operations"

* tag 'smp-urgent-2021-06-29' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  cpu/hotplug: Cure the cpusets trainwreck