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author | Stanislaw Gruszka <sgruszka@redhat.com> | 2012-03-02 10:43:28 +0100 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2012-03-19 08:57:58 -0700 |
commit | aaa136d348dc723f45667aa8b39eb58c7e7c4383 (patch) | |
tree | beef9c85935bbc5e4a06fb180a62e7f7aab4b4b3 /block | |
parent | 30503b5edf8c1e3204280534d416f31fcb277aee (diff) | |
download | lwn-aaa136d348dc723f45667aa8b39eb58c7e7c4383.tar.gz lwn-aaa136d348dc723f45667aa8b39eb58c7e7c4383.zip |
block: fix __blkdev_get and add_disk race condition
commit 9f53d2fe815b4011ff930a7b6db98385d45faa68 upstream.
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>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'block')
-rw-r--r-- | block/genhd.c | 32 |
1 files changed, 19 insertions, 13 deletions
diff --git a/block/genhd.c b/block/genhd.c index 8c0829a36376..091429d2c7c9 100644 --- a/block/genhd.c +++ b/block/genhd.c @@ -36,6 +36,7 @@ static DEFINE_IDR(ext_devt_idr); 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); @@ -602,6 +603,8 @@ void add_disk(struct gendisk *disk) 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)); @@ -1740,9 +1743,9 @@ module_param_cb(events_dfl_poll_msecs, &disk_events_dfl_poll_msecs_param_ops, &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; @@ -1755,16 +1758,6 @@ static void disk_add_events(struct gendisk *disk) 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); @@ -1773,8 +1766,21 @@ static void disk_add_events(struct gendisk *disk) 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); /* |