scsi: sg: Avoid race in error handling & drop bogus warn

commit d4e655c49f474deffaf5ed7e65034b8167ee39c8 upstream.

Commit 27f58c04a8f4 ("scsi: sg: Avoid sg device teardown race") introduced
an incorrect WARN_ON_ONCE() and missed a sequence where sg_device_destroy()
was used after scsi_device_put().

sg_device_destroy() is accessing the parent scsi_device request_queue which
will already be set to NULL when the preceding call to scsi_device_put()
removed the last reference to the parent scsi_device.

Drop the incorrect WARN_ON_ONCE() - allowing more than one concurrent
access to the sg device - and make sure sg_device_destroy() is not used
after scsi_device_put() in the error handling.

Link: https://lore.kernel.org/all/5375B275-D137-4D5F-BE25-6AF8ACAE41EF@linux.ibm.com
Fixes: 27f58c04a8f4 ("scsi: sg: Avoid sg device teardown race")
Cc: stable@vger.kernel.org
Signed-off-by: Alexander Wetzel <Alexander@wetzel-home.de>
Link: https://lore.kernel.org/r/20240401191038.18359-1-Alexander@wetzel-home.de
Tested-by: Sachin Sant <sachinp@linux.ibm.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index ff6894ce5404e7a3d873eb3ea67bec124117394a..b2d02dacaebd97439d54ec7909d4c0f2afee4474 100644 (file)
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -285,6 +285,7 @@ sg_open(struct inode *inode, struct file *filp)
        int dev = iminor(inode);
        int flags = filp->f_flags;
        struct request_queue *q;
+       struct scsi_device *device;
        Sg_device *sdp;
        Sg_fd *sfp;
        int retval;
@@ -301,11 +302,12 @@ sg_open(struct inode *inode, struct file *filp)
 
        /* This driver's module count bumped by fops_get in <linux/fs.h> */
        /* Prevent the device driver from vanishing while we sleep */
-       retval = scsi_device_get(sdp->device);
+       device = sdp->device;
+       retval = scsi_device_get(device);
        if (retval)
                goto sg_put;
 
-       retval = scsi_autopm_get_device(sdp->device);
+       retval = scsi_autopm_get_device(device);
        if (retval)
                goto sdp_put;
 
@@ -313,7 +315,7 @@ sg_open(struct inode *inode, struct file *filp)
         * check if O_NONBLOCK. Permits SCSI commands to be issued
         * during error recovery. Tread carefully. */
        if (!((flags & O_NONBLOCK) ||
-             scsi_block_when_processing_errors(sdp->device))) {
+             scsi_block_when_processing_errors(device))) {
                retval = -ENXIO;
                /* we are in error recovery for this device */
                goto error_out;
@@ -344,7 +346,7 @@ sg_open(struct inode *inode, struct file *filp)
 
        if (sdp->open_cnt < 1) {  /* no existing opens */
                sdp->sgdebug = 0;
-               q = sdp->device->request_queue;
+               q = device->request_queue;
                sdp->sg_tablesize = queue_max_segments(q);
        }
        sfp = sg_add_sfp(sdp);
@@ -370,10 +372,11 @@ sg_open(struct inode *inode, struct file *filp)
 error_mutex_locked:
        mutex_unlock(&sdp->open_rel_lock);
 error_out:
-       scsi_autopm_put_device(sdp->device);
+       scsi_autopm_put_device(device);
 sdp_put:
-       scsi_device_put(sdp->device);
-       goto sg_put;
+       kref_put(&sdp->d_ref, sg_device_destroy);
+       scsi_device_put(device);
+       return retval;
 }
 
 /* Release resources associated with a successful sg_open()
@@ -2233,7 +2236,6 @@ sg_remove_sfp_usercontext(struct work_struct *work)
                        "sg_remove_sfp: sfp=0x%p\n", sfp));
        kfree(sfp);
 
-       WARN_ON_ONCE(kref_read(&sdp->d_ref) != 1);
        kref_put(&sdp->d_ref, sg_device_destroy);
        scsi_device_put(device);
        module_put(THIS_MODULE);