UBI: fix race condition
This patch fixes a minor problem where we may fail to wake
upe the UBI background thread. This is not fatal at all,
it may just result at sligtly worse performace for a short
period of time, just because the thread will be woken up
when real I/O on the UBI starts.
Anywey, the issue is the race condition between
'ubi_attach_mtd_dev()' and 'ubi_thread()'. If we do not
serialize them, the 'wake_up_process()' call may be done
before 'ubi_thread()' went seep, but after it checked
'ubi->thread_enabled'.
This issue was spotted by Shin Hong <hongshin@gmail.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c
index 2c3269e..1405b55 100644
--- a/drivers/mtd/ubi/build.c
+++ b/drivers/mtd/ubi/build.c
@@ -380,7 +380,7 @@
* @ubi: UBI device description object
*
* This function returns zero in case of success and a negative error code in
- * case of failure. Note, this function destroys all volumes if it failes.
+ * case of failure. Note, this function destroys all volumes if it fails.
*/
static int uif_init(struct ubi_device *ubi)
{
@@ -871,9 +871,15 @@
ubi->beb_rsvd_pebs);
ubi_msg("max/mean erase counter: %d/%d", ubi->max_ec, ubi->mean_ec);
+ /*
+ * The below lock makes sure we do not race with 'ubi_thread()' which
+ * checks @ubi->thread_enabled. Otherwise we may fail to wake it up.
+ */
+ spin_lock(&ubi->wl_lock);
if (!DBG_DISABLE_BGT)
ubi->thread_enabled = 1;
wake_up_process(ubi->bgt_thread);
+ spin_unlock(&ubi->wl_lock);
ubi_devices[ubi_num] = ubi;
return ubi_num;