[SCSI] sd: avoid deadlocks when running under multipath

When multipathed systems run into an all-paths-down scenario
all devices might be dropped, too. This causes 'del_gendisk'
to be called, which will unregister the kobj_map->probe()
function for all disk device numbers.
When the device comes back the default ->probe() function
is run which will call __request_module(), which will
deadlock.
As 'del_gendisk' typically does _not_ trigger a module unload
the default ->probe() function is pointless anyway.
This patch implements a dummy ->probe() function, which will
just return NULL if the disk is not registered.
This will avoid the deadlock. Plus it'll speed up device
scanning.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index c1c5552..a37eda9 100644 (file)
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -504,6 +504,16 @@ static struct scsi_driver sd_template = {
 };
 
 /*
+ * Dummy kobj_map->probe function.
+ * The default ->probe function will call modprobe, which is
+ * pointless as this module is already loaded.
+ */
+static struct kobject *sd_default_probe(dev_t devt, int *partno, void *data)
+{
+       return NULL;
+}
+
+/*
  * Device no to disk mapping:
  * 
  *       major         disc2     disc  p1
@@ -2970,8 +2980,10 @@ static int sd_probe(struct device *dev)
 static int sd_remove(struct device *dev)
 {
        struct scsi_disk *sdkp;
+       dev_t devt;
 
        sdkp = dev_get_drvdata(dev);
+       devt = disk_devt(sdkp->disk);
        scsi_autopm_get_device(sdkp->device);
 
        async_synchronize_full_domain(&scsi_sd_probe_domain);
@@ -2981,6 +2993,9 @@ static int sd_remove(struct device *dev)
        del_gendisk(sdkp->disk);
        sd_shutdown(dev);
 
+       blk_register_region(devt, SD_MINORS, NULL,
+                           sd_default_probe, NULL, NULL);
+
        mutex_lock(&sd_ref_mutex);
        dev_set_drvdata(dev, NULL);
        put_device(&sdkp->dev);
@@ -3124,9 +3139,13 @@ static int __init init_sd(void)
 
        SCSI_LOG_HLQUEUE(3, printk("init_sd: sd driver entry point\n"));
 
-       for (i = 0; i < SD_MAJORS; i++)
-               if (register_blkdev(sd_major(i), "sd") == 0)
-                       majors++;
+       for (i = 0; i < SD_MAJORS; i++) {
+               if (register_blkdev(sd_major(i), "sd") != 0)
+                       continue;
+               majors++;
+               blk_register_region(sd_major(i), SD_MINORS, NULL,
+                                   sd_default_probe, NULL, NULL);
+       }
 
        if (!majors)
                return -ENODEV;
@@ -3185,8 +3204,10 @@ static void __exit exit_sd(void)
 
        class_unregister(&sd_disk_class);
 
-       for (i = 0; i < SD_MAJORS; i++)
+       for (i = 0; i < SD_MAJORS; i++) {
+               blk_unregister_region(sd_major(i), SD_MINORS);
                unregister_blkdev(sd_major(i), "sd");
+       }
 }
 
 module_init(init_sd);