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[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>
This commit is contained in:
Hannes Reinecke 2013-05-10 11:06:16 +02:00 committed by James Bottomley
parent 70288b4c8f
commit 0761df9c4b
1 changed files with 25 additions and 4 deletions
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29
drivers/scsi/sd.c
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@ -503,6 +503,16 @@ static struct scsi_driver sd_template = {
.eh_action = sd_eh_action,
};
/*
* 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:
*
@ -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);