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From:   Chengfeng Ye <dg573847474@gmail.com>
To:     james.smart@broadcom.com, dick.kennedy@broadcom.com,
        jejb@linux.ibm.com, martin.petersen@oracle.com,
        justin.tee@broadcom.com
Cc:     linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
        Chengfeng Ye <dg573847474@gmail.com>
Subject: [PATCH] scsi: lpfc: Fix potential deadlock on &phba->hbalock
Date:   Wed, 26 Jul 2023 15:53:42 +0000
Message-Id: <20230726155342.51623-1-dg573847474@gmail.com>
Precedence: bulk

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@gmail.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