sched/core: Prevent rescheduling when interrupts are disabled

In the Linux kernel, the following vulnerability has been resolved:

sched/core: Prevent rescheduling when interrupts are disabled

David reported a warning observed while loop testing kexec jump:

Interrupts enabled after irqrouter_resume+0x0/0x50

WARNING: CPU: 0 PID: 560 at drivers/base/syscore.c:103 syscore_resume+0x18a/0x220

kernel_kexec+0xf6/0x180

__do_sys_reboot+0x206/0x250

do_syscall_64+0x95/0x180

The corresponding interrupt flag trace:

hardirqs last enabled at (15573): [<ffffffffa8281b8e>] __up_console_sem+0x7e/0x90

hardirqs last disabled at (15580): [<ffffffffa8281b73>] __up_console_sem+0x63/0x90

That means __up_console_sem() was invoked with interrupts enabled. Further

instrumentation revealed that in the interrupt disabled section of kexec

jump one of the syscore_suspend() callbacks woke up a task, which set the

NEED_RESCHED flag. A later callback in the resume path invoked

cond_resched() which in turn led to the invocation of the scheduler:

__cond_resched+0x21/0x60

down_timeout+0x18/0x60

acpi_os_wait_semaphore+0x4c/0x80

acpi_ut_acquire_mutex+0x3d/0x100

acpi_ns_get_node+0x27/0x60

acpi_ns_evaluate+0x1cb/0x2d0

acpi_rs_set_srs_method_data+0x156/0x190

acpi_pci_link_set+0x11c/0x290

irqrouter_resume+0x54/0x60

syscore_resume+0x6a/0x200

kernel_kexec+0x145/0x1c0

__do_sys_reboot+0xeb/0x240

do_syscall_64+0x95/0x180

This is a long standing problem, which probably got more visible with

the recent printk changes. Something does a task wakeup and the

scheduler sets the NEED_RESCHED flag. cond_resched() sees it set and

invokes schedule() from a completely bogus context. The scheduler

enables interrupts after context switching, which causes the above

warning at the end.

Quite some of the code paths in syscore_suspend()/resume() can result in

triggering a wakeup with the exactly same consequences. They might not

have done so yet, but as they share a lot of code with normal operations

it's just a question of time.

The problem only affects the PREEMPT_NONE and PREEMPT_VOLUNTARY scheduling

models. Full preemption is not affected as cond_resched() is disabled and

the preemption check preemptible() takes the interrupt disabled flag into

account.

Cure the problem by adding a corresponding check into cond_resched().