On Fri, Jun 18, 2021 at 03:23:05PM -0700, Bhaumik Bhatt wrote:
> With spin_lock_bh(), it is possible that a tasklet processing data
> events gets scheduled out if another higher priority tasklet is
> ready to run. While the tasklet is sleeping, it can hold the event
> ring spinlock and block another tasklet, for example, one processing
> an M0 state change event, from acquiring it. This can starve the
> core which blocks in an attempt to acquire the spinlock until it
> gets released. Fix this issue by disabling pre-emption on the core
> processing data events and allow it to run to completion such that
> other tasklets do not block for long periods.
>
Are you sure?
IIUC, the tasklets priority is only used while trying to schedule the
next pending tasklet. But I don't think a high priority tasklet can
preempt the low priority one.
Please correct me if I'm wrong.
Thanks,
Mani
> Fixes: 1d3173a3bae7 ("bus: mhi: core: Add support for processing events from client device")
> Signed-off-by: Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>
> ---
> drivers/bus/mhi/core/main.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
> index 3775c77..02c8c09 100644
> --- a/drivers/bus/mhi/core/main.c
> +++ b/drivers/bus/mhi/core/main.c
> @@ -1036,11 +1036,12 @@ void mhi_ev_task(unsigned long data)
> {
> struct mhi_event *mhi_event = (struct mhi_event *)data;
> struct mhi_controller *mhi_cntrl = mhi_event->mhi_cntrl;
> + unsigned long flags;
>
> /* process all pending events */
> - spin_lock_bh(&mhi_event->lock);
> + spin_lock_irqsave(&mhi_event->lock, flags);
> mhi_event->process_event(mhi_cntrl, mhi_event, U32_MAX);
> - spin_unlock_bh(&mhi_event->lock);
> + spin_unlock_irqrestore(&mhi_event->lock, flags);
> }
>
> void mhi_ctrl_ev_task(unsigned long data)
> --
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> a Linux Foundation Collaborative Project
>
