The following commit has been merged into the sched/urgent branch of tip:

Commit-ID: c092dc7d88c1214e109591790c9021a0f734677a Gitweb: https://git.kernel.org/tip/c092dc7d88c1214e109591790c9021a0f734677a Author: Thomas Gleixner tglx@linutronix.de AuthorDate: Mon, 16 Dec 2024 14:20:56 +01:00 Committer: Ingo Molnar mingo@kernel.org CommitterDate: Thu, 27 Feb 2025 20:55:16 +01:00

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().

Reported-by: David Woodhouse dwmw@amazon.co.uk Signed-off-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Ingo Molnar mingo@kernel.org Tested-by: David Woodhouse dwmw@amazon.co.uk Cc: Peter Zijlstra peterz@infradead.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: stable@vger.kernel.org Closes: https://lore.kernel.org/all/7717fe2ac0ce5f0a2c43fdab8b11f4483d54a2a4.camel@i... --- kernel/sched/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 9aecd91..6718990 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7285,7 +7285,7 @@ out_unlock: #if !defined(CONFIG_PREEMPTION) || defined(CONFIG_PREEMPT_DYNAMIC) int __sched __cond_resched(void) { - if (should_resched(0)) { + if (should_resched(0) && !irqs_disabled()) { preempt_schedule_common(); return 1; }