linux-kernel - Re: [PATCH] scsi: lpfc: Fix potential deadlock on &phba->hbalock

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Date:   Wed, 26 Jul 2023 15:16:39 -0700
From:   Justin Tee <justin.tee@...adcom.com>
To:     Chengfeng Ye <dg573847474@...il.com>
Cc:     james.smart@...adcom.com, dick.kennedy@...adcom.com,
        jejb@...ux.ibm.com, martin.petersen@...cle.com,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi: lpfc: Fix potential deadlock on &phba->hbalock

Hi Chengfeng,

lpfc_cmpl_els_uvem is for the VMID feature that could only ever be
called on an SLI4 type HBA.
lpfc_sli_intr_handler can only ever be called on an SLI3 type HBA.

So, the deadlock being referred to can never happen.

Thanks,
Justin

On Wed, Jul 26, 2023 at 8:55 AM Chengfeng Ye <dg573847474@...il.com> wrote:
>
> As &phba->hbalock is acquired by hardirq such as lpfc_sli_intr_handler(),
> process context code acquiring the lock &phba->hbalock should disable
> irq, otherwise deadlock could happen if the irq preempt the execution
> while the lock is held in process context on the same CPU.
>
> Most lock acquicision site disables irq but inside the callback
> lpfc_cmpl_els_uvem() the lock is acquired without explicitly disable irq.
> The outside caller of this callback also seems not disable irq.
>
> [Deadlock Scenario]
> lpfc_cmpl_els_uvem()
>     -> spin_lock(&phba->hbalock)
>         <irq>
>         -> lpfc_sli_intr_handle()
>         -> spin_lock(&phba->hbalock); (deadlock here)
>
> This flaw was found by an experimental static analysis tool I am
> developing for irq-related deadlock.
>
> The patch fix the potential deadlock by spin_lock_irqsave() just like
> other callsite.
>
> Signed-off-by: Chengfeng Ye <dg573847474@...il.com>
> ---
>  drivers/scsi/lpfc/lpfc_els.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/scsi/lpfc/lpfc_els.c b/drivers/scsi/lpfc/lpfc_els.c
> index 2bad9954c355..9667b4937b3a 100644
> --- a/drivers/scsi/lpfc/lpfc_els.c
> +++ b/drivers/scsi/lpfc/lpfc_els.c
> @@ -12398,6 +12398,7 @@ lpfc_cmpl_els_uvem(struct lpfc_hba *phba, struct lpfc_iocbq *icmdiocb,
>         u32 ulp_word4 = get_job_word4(phba, rspiocb);
>         struct lpfc_dmabuf *dmabuf = icmdiocb->cmd_dmabuf;
>         struct lpfc_vmid *vmid;
> +       unsigned long flags;
>
>         vmid = vmid_context->vmp;
>         if (!ndlp || ndlp->nlp_state != NLP_STE_UNMAPPED_NODE)
> @@ -12419,11 +12420,11 @@ lpfc_cmpl_els_uvem(struct lpfc_hba *phba, struct lpfc_iocbq *icmdiocb,
>                                  ulp_status, ulp_word4);
>                 goto out;
>         }
> -       spin_lock(&phba->hbalock);
> +       spin_lock_irqsave(&phba->hbalock, flags);
>         /* Set IN USE flag */
>         vport->vmid_flag |= LPFC_VMID_IN_USE;
>         phba->pport->vmid_flag |= LPFC_VMID_IN_USE;
> -       spin_unlock(&phba->hbalock);
> +       spin_unlock_irqrestore(&phba->hbalock, flags);
>
>         if (vmid_context->instantiated) {
>                 write_lock(&vport->vmid_lock);
> --
> 2.17.1
>

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