Re: [PATCH v3 2/5] fs/filesystems.c: downgrade user-reachable WARN_ONCE() to pr_warn_once()

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+++ Eric Biggers [14/03/20 14:34 -0700]:
From: Eric Biggers <ebiggers@xxxxxxxxxx>

After request_module(), nothing is stopping the module from being
unloaded until someone takes a reference to it via try_get_module().

The WARN_ONCE() in get_fs_type() is thus user-reachable, via userspace
running 'rmmod' concurrently.

Since WARN_ONCE() is for kernel bugs only, not for user-reachable
situations, downgrade this warning to pr_warn_once().

Acked-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Jeff Vander Stoep <jeffv@xxxxxxxxxx>
Cc: Jessica Yu <jeyu@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: NeilBrown <neilb@xxxxxxxx>
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
---
fs/filesystems.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/filesystems.c b/fs/filesystems.c
index 77bf5f95362da..90b8d879fbaf3 100644
--- a/fs/filesystems.c
+++ b/fs/filesystems.c
@@ -272,7 +272,9 @@ struct file_system_type *get_fs_type(const char *name)
	fs = __get_fs_type(name, len);
	if (!fs && (request_module("fs-%.*s", len, name) == 0)) {
		fs = __get_fs_type(name, len);
-		WARN_ONCE(!fs, "request_module fs-%.*s succeeded, but still no fs?\n", len, name);
+		if (!fs)
+			pr_warn_once("request_module fs-%.*s succeeded, but still no fs?\n",
+				     len, name);

Hm, what was the rationale for warning only once again? It might be useful
for debugging issues to see each instance of request_module() failure
(and with which fs). However, I don't have a concrete use case to
support this argument, so:

Reviewed-by: Jessica Yu <jeyu@xxxxxxxxxx>



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