Re: [PATCH] nvme-fc: fix sleep-in-atomic-context bug caused by nvme_fc_rcv_ls_req

[James Smart]

On 10/2/2022 6:50 PM, duoming@xxxxxxxxxx wrote:
> Hello,
>
> On Sun, 2 Oct 2022 10:12:15 -0700 James Smart wrote:
>
> > On 10/1/2022 5:19 PM, Duoming Zhou wrote:
> > > The function lpfc_poll_timeout() is a timer handler that runs in an
> > > atomic context, but it calls "kzalloc(.., GFP_KERNEL)" that may sleep.
> > > As a result, the sleep-in-atomic-context bug will happen. The processes
> > > is shown below:
> > >
> > > lpfc_poll_timeout()
> > >    lpfc_sli_handle_fast_ring_event()
> > >     lpfc_sli_process_unsol_iocb()
> > >      lpfc_complete_unsol_iocb()
> > >       lpfc_nvme_unsol_ls_handler()
> > >        lpfc_nvme_handle_lsreq()
> > >         nvme_fc_rcv_ls_req()
> > >          kzalloc(sizeof(.., GFP_KERNEL) //may sleep
> > >
> > > This patch changes the gfp_t parameter of kzalloc() from GFP_KERNEL to
> > > GFP_ATOMIC in order to mitigate the bug.
> > >
> > > Fixes: 14fd1e98afaf ("nvme-fc: Add Disconnect Association Rcv support")
> > > Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
> > > ---
> > >    drivers/nvme/host/fc.c | 2 +-
> > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/nvme/host/fc.c b/drivers/nvme/host/fc.c
> > > index 127abaf9ba5..36698dfc8b3 100644
> > > --- a/drivers/nvme/host/fc.c
> > > +++ b/drivers/nvme/host/fc.c
> > > @@ -1754,7 +1754,7 @@ nvme_fc_rcv_ls_req(struct nvme_fc_remote_port *portptr,
> > >    	lsop = kzalloc(sizeof(*lsop) +
> > >    			sizeof(union nvmefc_ls_requests) +
> > >    			sizeof(union nvmefc_ls_responses),
> > > -			GFP_KERNEL);
> > > +			GFP_ATOMIC);
> > >    	if (!lsop) {
> > >    		dev_info(lport->dev,
> > >    			"RCV %s LS failed: No memory\n",
> >
> > I would prefer this was fixed within lpfc rather than introducing atomic
> > allocations (1st in either host or target transport).  It was introduced
> > by lpfc change in irq handling style.
>
> Thank your for your reply and suggestions!
>
> Do you think change the lpfc_poll_timeout() to a delayed_work is better?
>
> Best regards,
> Duoming Zhou

as a minimum: the lpfc_complete_unsol_iocb handler should be passing off 
the iocb to a work queue routine - so that the context changes so that 
either nvme host or nvmet ls callback routines can be called. If 
possible, it should do the axchg alloc - to avoid a GFP_ATOMIC there as 
well...

It's usually best for these nvme LS's and ELS's to be done in a slow 
path thread/work queue element. That may mean segmenting a little 
earlier in the path.

-- james