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().
