[PATCH AUTOSEL for 3.18 30/53] scsi: mac_esp: Replace bogus memory barrier with spinlock

[Sasha Levin]

From: Finn Thain <fth...@telegraphics.com.au>

[ Upstream commit 4da2b1eb230ba4ad19b58984dc52e05b1073df5f ]

Commit da244654c66e ("[SCSI] mac_esp: fix for quadras with two esp
chips") added mac_scsi_esp_intr() to handle the IRQ lines from a pair of
on-board ESP chips (a normal shared IRQ did not work).

Proper mutual exclusion was missing from that patch. This patch fixes
race conditions between comparison and assignment of esp_chips[]
pointers.

Signed-off-by: Finn Thain <fth...@telegraphics.com.au>
Reviewed-by: Michael Schmitz <schmitz...@gmail.com>
Signed-off-by: Martin K. Petersen <martin.peter...@oracle.com>
Signed-off-by: Sasha Levin <alexander.le...@microsoft.com>
---
 drivers/scsi/mac_esp.c | 33 +++++++++++++++++++++++----------
 1 file changed, 23 insertions(+), 10 deletions(-)

diff --git a/drivers/scsi/mac_esp.c b/drivers/scsi/mac_esp.c
index 994fc5caf036..79fb6a4f661f 100644
--- a/drivers/scsi/mac_esp.c
+++ b/drivers/scsi/mac_esp.c
@@ -55,6 +55,7 @@ struct mac_esp_priv {
        int error;
 };
 static struct esp *esp_chips[2];
+static DEFINE_SPINLOCK(esp_chips_lock);
 
 #define MAC_ESP_GET_PRIV(esp) ((struct mac_esp_priv *) \
                               platform_get_drvdata((struct platform_device *) \
@@ -562,15 +563,18 @@ static int esp_mac_probe(struct platform_device *dev)
        }
 
        host->irq = IRQ_MAC_SCSI;
-       esp_chips[dev->id] = esp;
-       mb();
-       if (esp_chips[!dev->id] == NULL) {
-               err = request_irq(host->irq, mac_scsi_esp_intr, 0, "ESP", NULL);
-               if (err < 0) {
-                       esp_chips[dev->id] = NULL;
-                       goto fail_free_priv;
-               }
+
+       /* The request_irq() call is intended to succeed for the first device
+        * and fail for the second device.
+        */
+       err = request_irq(host->irq, mac_scsi_esp_intr, 0, "ESP", NULL);
+       spin_lock(&esp_chips_lock);
+       if (err < 0 && esp_chips[!dev->id] == NULL) {
+               spin_unlock(&esp_chips_lock);
+               goto fail_free_priv;
        }
+       esp_chips[dev->id] = esp;
+       spin_unlock(&esp_chips_lock);
 
        err = scsi_esp_register(esp, &dev->dev);
        if (err)
@@ -579,8 +583,13 @@ static int esp_mac_probe(struct platform_device *dev)
        return 0;
 
 fail_free_irq:
-       if (esp_chips[!dev->id] == NULL)
+       spin_lock(&esp_chips_lock);
+       esp_chips[dev->id] = NULL;
+       if (esp_chips[!dev->id] == NULL) {
+               spin_unlock(&esp_chips_lock);
                free_irq(host->irq, esp);
+       } else
+               spin_unlock(&esp_chips_lock);
 fail_free_priv:
        kfree(mep);
 fail_free_command_block:
@@ -599,9 +608,13 @@ static int esp_mac_remove(struct platform_device *dev)
 
        scsi_esp_unregister(esp);
 
+       spin_lock(&esp_chips_lock);
        esp_chips[dev->id] = NULL;
-       if (!(esp_chips[0] || esp_chips[1]))
+       if (esp_chips[!dev->id] == NULL) {
+               spin_unlock(&esp_chips_lock);
                free_irq(irq, NULL);
+       } else
+               spin_unlock(&esp_chips_lock);
 
        kfree(mep);
 
-- 
2.14.1