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From:   linan666@huaweicloud.com
To:     dlemoal@kernel.org
Cc:     linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org,
        linan122@huawei.com, yukuai3@huawei.com, yi.zhang@huawei.com,
        houtao1@huawei.com, yangerkun@huawei.com
Subject: [PATCH v2] scsi: ata: Fix a race condition between scsi error handler and ahci interrupt
Date:   Tue,  5 Sep 2023 11:48:40 +0800
Message-Id: <20230905034840.478332-1-linan666@huaweicloud.com>
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From: Li Nan <linan122@huawei.com>

If a disk is removed and quickly inserted when an I/O error is processing,
the disk may not be able to be re-added. The function call timeline is as
follows:

  interrupt                            scsi_eh

  ahci_error_intr
   ata_port_freeze
    __ata_port_freeze
     =>ahci_freeze (turn IRQ off)
    ata_port_abort
     ata_do_link_abort
      ata_port_schedule_eh
       =>ata_std_sched_eh
        ata_eh_set_pending
	 set EH_PENDING
        scsi_schedule_eh
         shost->host_eh_scheduled++ (=1)
                                       scsi_error_handler
                                        =>ata_scsi_error
                                         ata_scsi_port_error_handler
					  clear EH_PENDING
                                          =>ahci_error_handler
                                          . sata_pmp_error_handler
                                          .  ata_eh_reset
                                          .   ata_eh_thaw_port
                                          .   . =>ahci_thaw (turn IRQ on)
  ahci_error_intr			  .   .
   ata_port_freeze			  .   .
    __ata_port_freeze			  .   .
     =>ahci_freeze (turn IRQ off)	  .   .
    ...					  .   .
        ata_eh_set_pending		  .   .
	 set EH_PENDING			  .   .
        scsi_schedule_eh		  .   .
         shost->host_eh_scheduled++ (=2)  .   .
					  .   clear EH_PENDING
					  check EH_PENDING
                                          =>ata_std_end_eh
                                           host->host_eh_scheduled = 0;

'host_eh_scheduled' is 0 and scsi eh thread will not be scheduled again.
The ata port remain freeze and will never be enabled.

Decrease ’host_eh_scheduled‘ instead of set it to 0 roughly and move
WARN_ON of nr_active_links to ata_scsi_port_error_handler().

Reported-by: luojian <luojian5@huawei.com>
Signed-off-by: Li Nan <linan122@huawei.com>
---
Changes in v2:
  - fix the bug by decrease 'host_eh_scheduled’
  - improve commit message.

 drivers/ata/libata-eh.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/ata/libata-eh.c b/drivers/ata/libata-eh.c
index 159ba6ba19eb..b9454756ecde 100644
--- a/drivers/ata/libata-eh.c
+++ b/drivers/ata/libata-eh.c
@@ -735,6 +735,12 @@ void ata_scsi_port_error_handler(struct Scsi_Host *host, struct ata_port *ap)
 	 */
 	ap->ops->end_eh(ap);
 
+	if (!ap->scsi_host->host_eh_scheduled) {
+		/* make sure nr_active_links is zero after EH */
+		WARN_ON(ap->nr_active_links);
+		ap->nr_active_links = 0;
+	}
+
 	spin_unlock_irqrestore(ap->lock, flags);
 	ata_eh_release(ap);
 
@@ -948,7 +954,7 @@ void ata_std_end_eh(struct ata_port *ap)
 {
 	struct Scsi_Host *host = ap->scsi_host;
 
-	host->host_eh_scheduled = 0;
+	host->host_eh_scheduled--;
 }
 EXPORT_SYMBOL(ata_std_end_eh);
 
@@ -3922,10 +3928,6 @@ void ata_eh_finish(struct ata_port *ap)
 			}
 		}
 	}
-
-	/* make sure nr_active_links is zero after EH */
-	WARN_ON(ap->nr_active_links);
-	ap->nr_active_links = 0;
 }
 
 /**
-- 
2.39.2