block: fix __blkdev_get and add_disk race condition
The following situation might occur:
__blkdev_get: add_disk:
register_disk()
get_gendisk()
disk_block_events()
disk->ev == NULL
disk_add_events()
__disk_unblock_events()
disk->ev != NULL
--ev->block
Then we unblock events, when they are suppose to be blocked. This can
trigger events related block/genhd.c warnings, but also can crash in
sd_check_events() or other places.
I'm able to reproduce crashes with the following scripts (with
connected usb dongle as sdb disk).
<snip>
DEV=/dev/sdb
ENABLE=/sys/bus/usb/devices/1-2/bConfigurationValue
function stop_me()
{
for i in `jobs -p` ; do kill $i 2> /dev/null ; done
exit
}
trap stop_me SIGHUP SIGINT SIGTERM
for ((i = 0; i < 10; i++)) ; do
while true; do fdisk -l $DEV 2>&1 > /dev/null ; done &
done
while true ; do
echo 1 > $ENABLE
sleep 1
echo 0 > $ENABLE
done
</snip>
I use the script to verify patch fixing oops in sd_revalidate_disk
http://marc.info/?l=linux-scsi&m=132935572512352&w=2
Without Jun'ichi Nomura patch titled "Fix NULL pointer dereference in
sd_revalidate_disk" or this one, script easily crash kernel within
a few seconds. With both patches applied I do not observe crash.
Unfortunately after some time (dozen of minutes), script will hung in:
[ 1563.906432] [<c08354f5>] schedule_timeout_uninterruptible+0x15/0x20
[ 1563.906437] [<c04532d5>] msleep+0x15/0x20
[ 1563.906443] [<c05d60b2>] blk_drain_queue+0x32/0xd0
[ 1563.906447] [<c05d6e00>] blk_cleanup_queue+0xd0/0x170
[ 1563.906454] [<c06d278f>] scsi_free_queue+0x3f/0x60
[ 1563.906459] [<c06d7e6e>] __scsi_remove_device+0x6e/0xb0
[ 1563.906463] [<c06d4aff>] scsi_forget_host+0x4f/0x60
[ 1563.906468] [<c06cd84a>] scsi_remove_host+0x5a/0xf0
[ 1563.906482] [<f7f030fb>] quiesce_and_remove_host+0x5b/0xa0 [usb_storage]
[ 1563.906490] [<f7f03203>] usb_stor_disconnect+0x13/0x20 [usb_storage]
Anyway I think this patch is some step forward.
As drawback, I do not teardown on sysfs file create error, because I do
not know how to nullify disk->ev (since it can be used). However add_disk
error handling practically does not exist too, and things will work
without this sysfs file, except events will not be exported to user
space.
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: stable@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/genhd.c b/block/genhd.c
index 23b4f70..b26c408 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -35,6 +35,7 @@
static struct device_type disk_type;
+static void disk_alloc_events(struct gendisk *disk);
static void disk_add_events(struct gendisk *disk);
static void disk_del_events(struct gendisk *disk);
static void disk_release_events(struct gendisk *disk);
@@ -601,6 +602,8 @@
disk->major = MAJOR(devt);
disk->first_minor = MINOR(devt);
+ disk_alloc_events(disk);
+
/* Register BDI before referencing it from bdev */
bdi = &disk->queue->backing_dev_info;
bdi_register_dev(bdi, disk_devt(disk));
@@ -1733,9 +1736,9 @@
&disk_events_dfl_poll_msecs, 0644);
/*
- * disk_{add|del|release}_events - initialize and destroy disk_events.
+ * disk_{alloc|add|del|release}_events - initialize and destroy disk_events.
*/
-static void disk_add_events(struct gendisk *disk)
+static void disk_alloc_events(struct gendisk *disk)
{
struct disk_events *ev;
@@ -1748,16 +1751,6 @@
return;
}
- if (sysfs_create_files(&disk_to_dev(disk)->kobj,
- disk_events_attrs) < 0) {
- pr_warn("%s: failed to create sysfs files for events\n",
- disk->disk_name);
- kfree(ev);
- return;
- }
-
- disk->ev = ev;
-
INIT_LIST_HEAD(&ev->node);
ev->disk = disk;
spin_lock_init(&ev->lock);
@@ -1766,8 +1759,21 @@
ev->poll_msecs = -1;
INIT_DELAYED_WORK(&ev->dwork, disk_events_workfn);
+ disk->ev = ev;
+}
+
+static void disk_add_events(struct gendisk *disk)
+{
+ if (!disk->ev)
+ return;
+
+ /* FIXME: error handling */
+ if (sysfs_create_files(&disk_to_dev(disk)->kobj, disk_events_attrs) < 0)
+ pr_warn("%s: failed to create sysfs files for events\n",
+ disk->disk_name);
+
mutex_lock(&disk_events_mutex);
- list_add_tail(&ev->node, &disk_events);
+ list_add_tail(&disk->ev->node, &disk_events);
mutex_unlock(&disk_events_mutex);
/*
