It is unsafe to return an entry pointer and release the map_entries_lock. So we should
not hold the map_entries_lock separately in firmware_map_find_entry() and
firmware_map_remove_entry(). Hold the map_entries_lock across find and remove
/sys/firmware/memmap/X operation.

And also, users of these two functions need to be careful to hold the lock when using
these two functions.

The suggestion is from Andrew Morton [off-list ref]

Signed-off-by: Tang Chen <redacted>
---
 drivers/firmware/memmap.c |   25 +++++++++++++++++--------
 1 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/drivers/firmware/memmap.c b/drivers/firmware/memmap.c
index 4211da5..940c4e9 100644
--- a/drivers/firmware/memmap.c
+++ b/drivers/firmware/memmap.c

@@ -188,23 +188,28 @@ static inline void remove_sysfs_fw_map_entry(struct firmware_map_entry *entry)
 }

 /*
- * Search memmap entry
+ * firmware_map_find_entry: Search memmap entry.
+ * @start: Start of the memory range.
+ * @end:   End of the memory range (exclusive).
+ * @type:  Type of the memory range.
+ *
+ * This function is to find the memmap entey of a given memory range.
+ * The caller must hold map_entries_lock, and must not release the lock
+ * until the processing of the returned entry has completed.
+ *
+ * Return pointer to the entry to be found on success, or NULL on failure.