RE: [PATCH] DAMON dbgfs_mk_context() error handling

["Pulavarty, Badari" <badari.pulavarty@intel.com>]

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Hi SI,

> Nice finding, thank you!  But, the return value of the debugfs call is intentionally ignored[2].  How about doing the duplicated name check in
> dbgfs_mk_context() itself before the debugfs_create_dir() call?
>
> [2] https://lore.kernel.org/linux-mm/20210205155902.31102-1-sjpark@amazon.com/

How about this?

Thanks,
Badari



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damon dbgfs_mk_context() should check to make sure there is no existing 
context with the same name. Otherwise, it will cause failure when we 
enabling the monitor.

Test case:

echo "off" >  /sys/kernel/debug/damon/monitor_on
echo "abc" > /sys/kernel/debug/damon/mk_context
echo "abc" > /sys/kernel/debug/damon/mk_context
echo <pid> > /sys/kernel/debug/damon/abc/target_ids
echo "on" > /sys/kernel/debug/damon/monitor_on  <<< fails 

Signed-off-by: Badari Pulavarty <badari.pulavarty@intel.com>
---
--- a/mm/damon/dbgfs.c	2022-08-15 14:27:38.308806431 -0700
+++ b/mm/damon/dbgfs.c	2022-08-15 14:33:31.661163048 -0700
@@ -817,6 +817,12 @@
 	if (!root)
 		return -ENOENT;
 
+	new_dir = debugfs_lookup(name, root);
+	if (new_dir) {
+		dput(new_dir);
+		return -EEXIST;
+	}
+
 	new_dir = debugfs_create_dir(name, root);
 	dbgfs_dirs[dbgfs_nr_ctxs] = new_dir;