From: Kalesh Singh kaleshsingh@google.com

Commit 78ff64081949 ("vfs: Convert tracefs to use the new mount API") converted tracefs to use the new mount APIs caused mount options (e.g. gid=<gid>) to not take effect.

The tracefs superblock can be updated from multiple paths: - on fs_initcall() to init_trace_printk_function_export() - from a work queue to initialize eventfs tracer_init_tracefs_work_func() - fsconfig() syscall to mount or remount of tracefs

The tracefs superblock root inode gets created early on in init_trace_printk_function_export().

With the new mount API, tracefs effectively uses get_tree_single() instead of the old API mount_single().

Previously, mount_single() ensured that the options are always applied to the superblock root inode: (1) If the root inode didn't exist, call fill_super() to create it and apply the options. (2) If the root inode exists, call reconfigure_single() which effectively calls tracefs_apply_options() to parse and apply options to the subperblock's fs_info and inode and remount eventfs (if necessary)

On the other hand, get_tree_single() effectively calls vfs_get_super() which: (3) If the root inode doesn't exists, calls fill_super() to create it and apply the options. (4) If the root inode already exists, updates the fs_context root with the superblock's root inode.

(4) above is always the case for tracefs mounts, since the super block's root inode will already be created by init_trace_printk_function_export().

This means that the mount options get ignored: - Since it isn't applied to the superblock's root inode, it doesn't get inherited by the children. - Since eventfs is initialized from a separate work queue and before call to mount with the options, and it doesn't get remounted for mount.

Ensure that the mount options are applied to the super block and eventfs is remounted to respect the mount options.

To understand this better, if fstab has the following:

tracefs /sys/kernel/tracing tracefs nosuid,nodev,noexec,gid=tracing 0 0

On boot up, permissions look like:

# ls -l /sys/kernel/tracing/trace -rw-r----- 1 root root 0 Nov 1 08:37 /sys/kernel/tracing/trace

When it should look like:

# ls -l /sys/kernel/tracing/trace -rw-r----- 1 root tracing 0 Nov 1 08:37 /sys/kernel/tracing/trace

Link: https://lore.kernel.org/r/536e99d3-345c-448b-adee-a21389d7ab4b@redhat.com/

Cc: Eric Sandeen sandeen@redhat.com Cc: Mathieu Desnoyers mathieu.desnoyers@efficios.com Cc: Shuah Khan shuah@kernel.org Cc: Ali Zahraee ahzahraee@gmail.com Cc: Christian Brauner brauner@kernel.org Cc: David Howells dhowells@redhat.com Cc: Steven Rostedt rostedt@goodmis.org Cc: Masami Hiramatsu mhiramat@kernel.org Cc: stable@vger.kernel.org Fixes: 78ff64081949 ("vfs: Convert tracefs to use the new mount API") Link: https://lore.kernel.org/20241030171928.4168869-2-kaleshsingh@google.com Signed-off-by: Kalesh Singh kaleshsingh@google.com Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org --- fs/tracefs/inode.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c index 1748dff58c3b..cfc614c638da 100644 --- a/fs/tracefs/inode.c +++ b/fs/tracefs/inode.c @@ -392,6 +392,9 @@ static int tracefs_reconfigure(struct fs_context *fc) struct tracefs_fs_info *sb_opts = sb->s_fs_info; struct tracefs_fs_info *new_opts = fc->s_fs_info;

+ if (!new_opts) + return 0; + sync_filesystem(sb); /* structure copy of new mount options to sb */ *sb_opts = *new_opts; @@ -478,14 +481,17 @@ static int tracefs_fill_super(struct super_block *sb, struct fs_context *fc) sb->s_op = &tracefs_super_operations; sb->s_d_op = &tracefs_dentry_operations;

- tracefs_apply_options(sb, false); - return 0; }

static int tracefs_get_tree(struct fs_context *fc) { - return get_tree_single(fc, tracefs_fill_super); + int err = get_tree_single(fc, tracefs_fill_super); + + if (err) + return err; + + return tracefs_reconfigure(fc); }

static void tracefs_free_fc(struct fs_context *fc)