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

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Date:   Mon, 3 Oct 2022 10:48:31 -0700
From:   James Smart <jsmart2021@...il.com>
To:     duoming@....edu.cn
Cc:     linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        james.smart@...adcom.com, kbusch@...nel.org, axboe@...com,
        hch@....de, sagi@...mberg.me
Subject: Re: [PATCH] nvme-fc: fix sleep-in-atomic-context bug caused by
 nvme_fc_rcv_ls_req

On 10/2/2022 7:56 PM, James Smart wrote:
> On 10/2/2022 6:50 PM, duoming@....edu.cn 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@....edu.cn>
>>>> ---
>>>>    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
> 

looking further...   lpfc_poll_timeout() should only be used on an SLI-3 
adapter.  The existing SLI-3 adapters don't support NVMe. So I'm a 
little confused by this stack trace.

Can you describe what the system config/software setup is and 
specifically what lpfc adapter is being used (dmesg attachment logs are 
sufficient, or lspci output).

-- james