Re: [PATCH] time/sched_clock: Call enable_sched_clock_irqtime() with IRQs enabled

[Herve Codina <herve.codina@bootlin.com>]

Hi Benoît,

On Fri, 13 Nov 2026 17:40:09 +0100
Benoît Monin <benoit.monin@bootlin.com> wrote:

> sched_clock_register() disables interrupts with local_irq_save() and
> calls enable_sched_clock_irqtime() before restoring them.
> 
> With CONFIG_IRQ_TIME_ACCOUNTING, enable_sched_clock_irqtime() calls
> static_branch_enable(). With CONFIG_JUMP_LABEL and CONFIG_HOTPLUG_CPU,
> this takes cpus_read_lock(), which eventually calls might_sleep() from
> percpu_down_read_internal(). So with CONFIG_DEBUG_ATOMIC_SLEEP the
> following is reported:
> 
>   BUG: sleeping function called from invalid context at include/linux/percpu-rwsem.h:51
>   ...
>   Call Trace:
>   ...
>   [<a8000001008ad9c4>] __might_resched+0x3ac/0x3d0
>   [<a8000001008598b0>] percpu_down_read_internal.constprop.0+0x30/0x1b8
>   [<a800000100af5ddc>] static_key_enable+0x14/0x30
>   [<a80000010099b600>] sched_clock_register+0x2a0/0x370
>   ...
> 
> Most callers of sched_clock_register() are early init functions,
> for which might_sleep() stays silent because system_state is still
> SYSTEM_BOOTING. However, platform drivers such as timer-nxp-stm,
> timer-ti-dm, timer-mediatek and timer-rzn1, as well as the mips-gic-timer
> promotion work, call it later, where the warning is reported.
> 
> Only the sched_clock data update requires interrupts to be disabled.
> Enabling IRQ time accounting only flips a static branch, so restore
> interrupts before calling enable_sched_clock_irqtime().
> 
> Fixes: 2707745533d6 ("time/sched_clock: Disable interrupts in sched_clock_register()")
> Reported-by: Chen-Yu Tsai <wenst@chromium.org>
> Closes: https://lore.kernel.org/lkml/20261109095036.GA722431@google.com/
> Signed-off-by: Benoît Monin <benoit.monin@bootlin.com>
> ---
> Found the sleeping-in-atomic warning while working on the GIC
> synchronization series [1] and testing configuration options on the
> Mobileye EyeQ6H SoC, but the issue is not limited to that clock source.
> 
> Chen-Yu Tsai reported the same issue with timer-mediatek.
> 
> I also discussed the issue with my colleague Hervé, who reproduced the
> BUG on a board using timer-rzn1.
> 
> [1]: https://lore.kernel.org/lkml/20260929-sync-gic-counters-v4-0-ec70c4b60434@bootlin.com/
> ---
>  kernel/time/sched_clock.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)

And I confirm that the patch fixes the BUG reproduced on my RZ/N1 board.

Tested-by: Herve Codina <herve.codina@bootlin.com>

Best regards,
Hervé