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Subject[PATCH v4 2/5] fs/filesystems.c: downgrade user-reachable WARN_ONCE() to pr_warn_once()
From: Eric Biggers <>

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().

Keep it printed once only, since the intent of this warning is to detect
a bug in modprobe at boot time. Printing the warning more than once
wouldn't really provide any useful extra information.

Fixes: 41124db869b7 ("fs: warn in case userspace lied about modprobe return")
Acked-by: Luis Chamberlain <>
Reviewed-by: Jessica Yu <>
Cc: <> # v4.13+
Cc: Alexei Starovoitov <>
Cc: Andrew Morton <>
Cc: Greg Kroah-Hartman <>
Cc: Jeff Vander Stoep <>
Cc: Kees Cook <>
Cc: NeilBrown <>
Signed-off-by: Eric Biggers <>
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);

if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
 \ /
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