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Message-ID: <20230516160753.32317-4-rf@opensource.cirrus.com>
Date: Tue, 16 May 2023 17:07:51 +0100
From: Richard Fitzgerald <rf@...nsource.cirrus.com>
To: <gregkh@...uxfoundation.org>, <rafael@...nel.org>
CC: <linux-kernel@...r.kernel.org>, <patches@...nsource.cirrus.com>,
Richard Fitzgerald <rf@...nsource.cirrus.com>
Subject: [PATCH 3/5] debugfs: Update debugfs_create_str() kerneldoc to warn about pointer race
Add a warning to the debugfs_create_str() kerneldoc that the char * pointer
value must not change after the function returns, because of a race with
debugfs_read_file_str() accessing the pointer.
The only safe case is a change from NULL to non-NULL because in that case
debugfs_read_file_str() will see either the NULL or the valid pointer.
Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
---
fs/debugfs/file.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index 0c039a3d9a42..77794871f26d 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -938,11 +938,18 @@ static const struct file_operations fops_str_wo = {
* directory dentry if set. If this parameter is %NULL, then the
* file will be created in the root of the debugfs filesystem.
* @value: a pointer to the variable that the file should read to and write
- * from.
+ * from. The char* pointer must not change, except from NULL to
+ * non-NULL.
*
* This function creates a file in debugfs with the given name that
* contains the value of the variable @value. If the @mode variable is so
* set, it can be read from, and written to.
+ *
+ * The char* pointed to by @value must not change after calling this
+ * function EXCEPT that it may change from NULL to non-NULL. This is to
+ * prevent the file read from accessing a stale pointer. A change from
+ * NULL to non-NULL is the only safe change, because the read will
+ * instantaneously see either NULL or the valid pointer.
*/
void debugfs_create_str(const char *name, umode_t mode,
struct dentry *parent, char **value)
--
2.30.2
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