ubi: Fix races around ubi_refill_pools()

commit 2e8f08de upstream.

When writing a new Fastmap the first thing that happens
is refilling the pools in memory.
At this stage it is possible that new PEBs from the new pools
get already claimed and written with data.
If this happens before the new Fastmap data structure hits the
flash and we face power cut the freshly written PEB will not
scanned and unnoticed.

Solve the issue by locking the pools until Fastmap is written.

Fixes: dbb7d2a8 ("UBI: Add fastmap core")
Signed-off-by: Richard Weinberger <richard@nod.at>
[bwh: Backported to 3.16:
 - Adjust filename, context, indentation
 - s/ubi->fm_eba_sem/ubi->fm_sem/]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/mtd/ubi/eba.c

@@ -1021,6 +1021,8 @@ int ubi_eba_copy_leb(struct ubi_device *ubi, int from, int to,
 	struct ubi_volume *vol;
 	uint32_t crc;
 
+	ubi_assert(rwsem_is_locked(&ubi->fm_sem));
+
 	vol_id = be32_to_cpu(vid_hdr->vol_id);
 	lnum = be32_to_cpu(vid_hdr->lnum);
 
@@ -1189,9 +1191,7 @@ int ubi_eba_copy_leb(struct ubi_device *ubi, int from, int to,
 	}
 
 	ubi_assert(vol->eba_tbl[lnum] == from);
-	down_read(&ubi->fm_sem);
 	vol->eba_tbl[lnum] = to;
-	up_read(&ubi->fm_sem);
 
 out_unlock_buf:
 	mutex_unlock(&ubi->buf_mutex);

drivers/mtd/ubi/fastmap.c

@@ -1413,22 +1413,30 @@ int ubi_update_fastmap(struct ubi_device *ubi)
 	struct ubi_wl_entry *tmp_e;
 
 	mutex_lock(&ubi->fm_mutex);
+	down_write(&ubi->work_sem);
+	down_write(&ubi->fm_sem);
 
 	ubi_refill_pools(ubi);
 
 	if (ubi->ro_mode || ubi->fm_disabled) {
+		up_write(&ubi->fm_sem);
+		up_write(&ubi->work_sem);
 		mutex_unlock(&ubi->fm_mutex);
 		return 0;
 	}
 
 	ret = ubi_ensure_anchor_pebs(ubi);
 	if (ret) {
+		up_write(&ubi->fm_sem);
+		up_write(&ubi->work_sem);
 		mutex_unlock(&ubi->fm_mutex);
 		return ret;
 	}
 
 	new_fm = kzalloc(sizeof(*new_fm), GFP_KERNEL);
 	if (!new_fm) {
+		up_write(&ubi->fm_sem);
+		up_write(&ubi->work_sem);
 		mutex_unlock(&ubi->fm_mutex);
 		return -ENOMEM;
 	}
@@ -1539,16 +1547,14 @@ int ubi_update_fastmap(struct ubi_device *ubi)
 		new_fm->e[0]->ec = tmp_e->ec;
 	}
 
-	down_write(&ubi->work_sem);
-	down_write(&ubi->fm_sem);
 	ret = ubi_write_fastmap(ubi, new_fm);
-	up_write(&ubi->fm_sem);
-	up_write(&ubi->work_sem);
 
 	if (ret)
 		goto err;
 
 out_unlock:
+	up_write(&ubi->fm_sem);
+	up_write(&ubi->work_sem);
 	mutex_unlock(&ubi->fm_mutex);
 	kfree(old_fm);
 	return ret;

drivers/mtd/ubi/wl.c

@@ -653,6 +653,8 @@ static struct ubi_wl_entry *get_peb_for_wl(struct ubi_device *ubi)
 	struct ubi_fm_pool *pool = &ubi->fm_wl_pool;
 	int pnum;
 
+	ubi_assert(rwsem_is_locked(&ubi->fm_sem));
+
 	if (pool->used == pool->size || !pool->size) {
 		/* We cannot update the fastmap here because this
 		 * function is called in atomic context.
@@ -889,7 +891,7 @@ int ubi_is_erase_work(struct ubi_work *wrk)
  * failure.
  */
 static int schedule_erase(struct ubi_device *ubi, struct ubi_wl_entry *e,
-			  int vol_id, int lnum, int torture)
+			  int vol_id, int lnum, int torture, bool nested)
 {
 	struct ubi_work *wl_wrk;
 
@@ -909,6 +911,9 @@ static int schedule_erase(struct ubi_device *ubi, struct ubi_wl_entry *e,
 	wl_wrk->lnum = lnum;
 	wl_wrk->torture = torture;
 
+	if (nested)
+		__schedule_ubi_work(ubi, wl_wrk);
+	else
 		schedule_ubi_work(ubi, wl_wrk);
 	return 0;
 }
@@ -982,7 +987,7 @@ int ubi_wl_put_fm_peb(struct ubi_device *ubi, struct ubi_wl_entry *fm_e,
 	spin_unlock(&ubi->wl_lock);
 
 	vol_id = lnum ? UBI_FM_DATA_VOLUME_ID : UBI_FM_SB_VOLUME_ID;
-	return schedule_erase(ubi, e, vol_id, lnum, torture);
+	return schedule_erase(ubi, e, vol_id, lnum, torture, true);
 }
 #endif
 
@@ -1015,6 +1020,7 @@ static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
 	if (!vid_hdr)
 		return -ENOMEM;
 
+	down_read(&ubi->fm_sem);
 	mutex_lock(&ubi->move_mutex);
 	spin_lock(&ubi->wl_lock);
 	ubi_assert(!ubi->move_from && !ubi->move_to);
@@ -1241,6 +1247,7 @@ static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
 
 	dbg_wl("done");
 	mutex_unlock(&ubi->move_mutex);
+	up_read(&ubi->fm_sem);
 	return 0;
 
 	/*
@@ -1282,6 +1289,7 @@ static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
 	}
 
 	mutex_unlock(&ubi->move_mutex);
+	up_read(&ubi->fm_sem);
 	return 0;
 
 out_error:
@@ -1303,6 +1311,7 @@ static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
 out_ro:
 	ubi_ro_mode(ubi);
 	mutex_unlock(&ubi->move_mutex);
+	up_read(&ubi->fm_sem);
 	ubi_assert(err != 0);
 	return err < 0 ? err : -EIO;
 
@@ -1310,6 +1319,7 @@ static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
 	ubi->wl_scheduled = 0;
 	spin_unlock(&ubi->wl_lock);
 	mutex_unlock(&ubi->move_mutex);
+	up_read(&ubi->fm_sem);
 	ubi_free_vid_hdr(ubi, vid_hdr);
 	return 0;
 }
@@ -1411,7 +1421,7 @@ int ubi_ensure_anchor_pebs(struct ubi_device *ubi)
 
 	wrk->anchor = 1;
 	wrk->func = &wear_leveling_worker;
-	schedule_ubi_work(ubi, wrk);
+	__schedule_ubi_work(ubi, wrk);
 	return 0;
 }
 #endif
@@ -1477,7 +1487,7 @@ static int erase_worker(struct ubi_device *ubi, struct ubi_work *wl_wrk,
 		int err1;
 
 		/* Re-schedule the LEB for erasure */
-		err1 = schedule_erase(ubi, e, vol_id, lnum, 0);
+		err1 = schedule_erase(ubi, e, vol_id, lnum, 0, false);
 		if (err1) {
 			err = err1;
 			goto out_ro;
@@ -1633,7 +1643,7 @@ int ubi_wl_put_peb(struct ubi_device *ubi, int vol_id, int lnum,
 	}
 	spin_unlock(&ubi->wl_lock);
 
-	err = schedule_erase(ubi, e, vol_id, lnum, torture);
+	err = schedule_erase(ubi, e, vol_id, lnum, torture, false);
 	if (err) {
 		spin_lock(&ubi->wl_lock);
 		wl_tree_add(e, &ubi->used);
@@ -1922,7 +1932,7 @@ int ubi_wl_init(struct ubi_device *ubi, struct ubi_attach_info *ai)
 		e->ec = aeb->ec;
 		ubi_assert(!ubi_is_fm_block(ubi, e->pnum));
 		ubi->lookuptbl[e->pnum] = e;
-		if (schedule_erase(ubi, e, aeb->vol_id, aeb->lnum, 0)) {
+		if (schedule_erase(ubi, e, aeb->vol_id, aeb->lnum, 0, false)) {
 			kmem_cache_free(ubi_wl_entry_slab, e);
 			goto out_free;
 		}