[PATCH] scsi: sg: Avoid sg device teardown race

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sg_remove_sfp_usercontext() must not use sg_device_destroy() after
calling scsi_device_put().

sg_device_destroy() is accessling the device queue. Which will be set to
NULL if scsi_device_put() removes the last reference to the sg device.

Link: https://lore.kernel.org/r/20240305150509.23896-1-Alexander@xxxxxxxxxxxxxx
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Alexander Wetzel <Alexander@xxxxxxxxxxxxxx>
---

This is my best shot for a real fix of the issue.
I confirmed with printk's that I get the NULL pointer freeze ony when
scsi_device_put() is deleting the last reference to the device.
In the cases where it's not crashing there is still a reference left
after the call.

I don't see any obvious down side of simply swapping the calls.
The alternative would by my first patch, just without the WARN_ON.

Alexander
---
 drivers/scsi/sg.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 86210e4dd0d3..80e0d1981191 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -2232,8 +2232,8 @@ sg_remove_sfp_usercontext(struct work_struct *work)
 			"sg_remove_sfp: sfp=0x%p\n", sfp));
 	kfree(sfp);
 
-	scsi_device_put(sdp->device);
 	kref_put(&sdp->d_ref, sg_device_destroy);
+	scsi_device_put(sdp->device);
 	module_put(THIS_MODULE);
 }
 
-- 
2.44.0





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