Re: [PATCH v2 01/13] mailbox: pcc: Fix the possible race in updation of chan_in_use flag

[Sudeep Holla <sudeep.holla@arm.com>]

On Tue, Mar 11, 2025 at 07:40:53PM +0800, lihuisong (C) wrote:
> 
> 在 2025/3/6 0:38, Sudeep Holla 写道:
> > From: Huisong Li <lihuisong@huawei.com>
> > 
> > The function mbox_chan_received_data() calls the Rx callback of the
> > mailbox client driver. The callback might set chan_in_use flag from
> > pcc_send_data(). This flag's status determines whether the PCC channel
> > is in use.
> > 
> > However, there is a potential race condition where chan_in_use is
> > updated incorrectly due to concurrency between the interrupt handler
> > (pcc_mbox_irq()) and the command sender(pcc_send_data()).
> > 
> > The 'chan_in_use' flag of a channel is set to true after sending a
> > command. And the flag of the new command may be cleared erroneous by
> > the interrupt handler afer mbox_chan_received_data() returns,
> > 
> > As a result, the interrupt being level triggered can't be cleared in
> > pcc_mbox_irq() and it will be disabled after the number of handled times
> > exceeds the specified value. The error log is as follows:
> > 
> >    |  kunpeng_hccs HISI04B2:00: PCC command executed timeout!
> >    |  kunpeng_hccs HISI04B2:00: get port link status info failed, ret = -110
> >    |  irq 13: nobody cared (try booting with the "irqpoll" option)
> >    |  Call trace:
> >    |   dump_backtrace+0x0/0x210
> >    |   show_stack+0x1c/0x2c
> >    |   dump_stack+0xec/0x130
> >    |   __report_bad_irq+0x50/0x190
> >    |   note_interrupt+0x1e4/0x260
> >    |   handle_irq_event+0x144/0x17c
> >    |   handle_fasteoi_irq+0xd0/0x240
> >    |   __handle_domain_irq+0x80/0xf0
> >    |   gic_handle_irq+0x74/0x2d0
> >    |   el1_irq+0xbc/0x140
> >    |   mnt_clone_write+0x0/0x70
> >    |   file_update_time+0xcc/0x160
> >    |   fault_dirty_shared_page+0xe8/0x150
> >    |   do_shared_fault+0x80/0x1d0
> >    |   do_fault+0x118/0x1a4
> >    |   handle_pte_fault+0x154/0x230
> >    |   __handle_mm_fault+0x1ac/0x390
> >    |   handle_mm_fault+0xf0/0x250
> >    |   do_page_fault+0x184/0x454
> >    |   do_translation_fault+0xac/0xd4
> >    |   do_mem_abort+0x44/0xb4
> >    |   el0_da+0x40/0x74
> >    |   el0_sync_handler+0x60/0xb4
> >    |   el0_sync+0x168/0x180
> >    |  handlers:
> >    |   pcc_mbox_irq
> >    |  Disabling IRQ #13
> > 
> > To solve this issue, pcc_mbox_irq() must clear 'chan_in_use' flag before
> > the call to mbox_chan_received_data().
> > 
> > Signed-off-by: Huisong Li <lihuisong@huawei.com>
> > (sudeep.holla: Minor updates to the subject and commit message)
> > Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
> > ---
> >   drivers/mailbox/pcc.c | 7 ++++++-
> >   1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
> > index 82102a4c5d68839170238540a6fed61afa5185a0..f2e4087281c70eeb5b9b33371596613a371dff4f 100644
> > --- a/drivers/mailbox/pcc.c
> > +++ b/drivers/mailbox/pcc.c
> > @@ -333,10 +333,15 @@ static irqreturn_t pcc_mbox_irq(int irq, void *p)
> >   	if (pcc_chan_reg_read_modify_write(&pchan->plat_irq_ack))
> >   		return IRQ_NONE;
> > +	/*
> > +	 * Clear this flag immediately after updating interrupt ack register
> > +	 * to avoid possible race in updatation of the flag from
> > +	 * pcc_send_data() that could execute from mbox_chan_received_data()
> This comment may be inappropriate becuase of the moving of clearing
> interrupt ack register in patch 2/13.
> I suggested that fix it in this patch or patch 2/13.

Right, I did think of updating or did update and missed to commit.
I wanted to update something like:
"
Clear this flag after updating interrupt ack register and just before
mbox_chan_received_data() which might call pcc_send_data() where the
flag is set again to start new transfer
"

Hope that is more apt to the current situation.

-- 
Regards,
Sudeep