fs/proc/internal.h: fix up comment

Document what ->pde_unload_lock actually does.

Link: http://lkml.kernel.org/r/20180103185120.GB31849@avx2
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/internal.h

@@ -38,7 +38,8 @@ struct proc_dir_entry {
 	atomic_t in_use;
 	atomic_t count;		/* use count */
 	struct list_head pde_openers;	/* who did ->open, but not ->release */
-	spinlock_t pde_unload_lock; /* proc_fops checks and pde_users bumps */
+	/* protects ->pde_openers and all struct pde_opener instances */
+	spinlock_t pde_unload_lock;
 	struct completion *pde_unload_completion;
 	const struct inode_operations *proc_iops;
 	const struct file_operations *proc_fops;