Re: [PATCH 1/6] sched: Unbreak wakeups

Greg Kroah-Hartman
2021-06-02T13:58:22Z

On Wed, Jun 02, 2021 at 03:12:26PM +0200, Peter Zijlstra wrote:
> Remove broken task->state references and let wake_up_process() DTRT.
>
> The anti-pattern in these patches breaks the ordering of ->state vs
> COND as described in the comment near set_current_state() and can lead
> to missed wakeups:
>
> (OoO load, observes RUNNING)<-.
> for (;;) { |
> t->state = UNINTERRUPTIBLE; |
> smp_mb(); ,-----> ,' (OoO load, observed !COND)
> | |
> | | COND = 1;
> | `- if (t->state != RUNNING)
> | wake_up_process(t); // not done
> if (COND) ---------'
> break;
> schedule(); // forever waiting
> }
> t->state = TASK_RUNNING;
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
> drivers/net/ethernet/qualcomm/qca_spi.c | 6 ++----
> drivers/usb/gadget/udc/max3420_udc.c | 15 +++++----------
> drivers/usb/host/max3421-hcd.c | 3 +--
> kernel/softirq.c | 2 +-
> 4 files changed, 9 insertions(+), 17 deletions(-)

For USB stuff:

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>