On Mon, Oct 28, 2024 at 8:00 PM Eric Sandeen <sand...@redhat.com> wrote:
>
> On 10/28/24 4:43 PM, Kalesh Singh wrote:
> > Commit 78ff64081949 ("vfs: Convert tracefs to use the new mount API")
> > tracefs to use the new mount APIs caused mounting with the gid=<gid>
> > option to not take effect.
>
> Or any other mount options. I'm sure this isn't unique to gid, right?
> So, might want to fix the commit title.Hi Eric, You are right, they same applies to any of the mount options. I'll update the commit text for v2. > > > The tracefs superblock can be updated from multiple paths: > > - on fs_initcall() to init_trace_printk_function_export() > > - form a work queue to initialize eventfs > > tracer_init_tracefs_work_func() > > - fsconfig() syscall to mount of remount sysfs > > > > The tracefs super block 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 alway applied to > > the superblock root inode: > > (1) If the root inode didn't exist, called fill_super() to create it > > and apply the options. > > (2) If the root inode exists, called reconfigure_single() which > > effectively called 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. > > I'm honestly a little lost here, but given the differences between > mount_single() > and get_tree_single() - are other get_tree_single() users similarly broken? > I'm not sure if other filesystems are broken in the same way. The issue happened for tracefs due to the fact that the sb root is created before calling mount -- from init_trace_printk_function_export(). If there are other filesystems that have similar early initialization (before mount) they may be broken as well. > Should get_tree_single() just be calling reconfigure_single() internally like > mount_single() did? The comment in reconfigure_single() confuses me. > > > (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 reminds me a little of > > commit a6097180d884ddab769fb25588ea8598589c218c > Author: NeilBrown <ne...@suse.de> > Date: Mon Jan 17 09:07:26 2022 +1100 > > devtmpfs regression fix: reconfigure on each mount > Interesting, yes it seems like the same root cause. i.e. devtmpfs sb root is created early on from kernel_init() .... --> driver_init() ---> devtmpfs_init() which setups up the root inode for devtmpfs in shmem_get_tree() ... -> vfs_get_super(); which is the case (4), meaning that it would have ignored the options on mount for the same reason: the superblock root indoe already exists. I'm not very familiar with the filesystem area. If this is a common scenario, maybe there needs to be a separate API to handle this case? > > This means that the gid mount option gets ignored: > > - Since it isn't applied to the super block's root inode, it doesn't > > get inherited by the children. > > - Since eventfs is initialized from form 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 new mount options. > > > > [1] > > https://lore.kernel.org/r/536e99d3-345c-448b-adee-a21389d7a...@redhat.com/ > > > > Fixes: 78ff64081949 ("vfs: Convert tracefs to use the new mount API") > > Cc: David Howells <dhowe...@redhat.com> > > Cc: Steven Rostedt <rost...@goodmis.org> > > Cc: Masami Hiramatsu <mhira...@kernel.org> > > Signed-off-by: Kalesh Singh <kaleshsi...@google.com> > > --- > > 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; > > Can this really happen? >From init_trace_printk_function_export() the first time the super block is allocated and added to file_system_type->fs_supers; fc->s_fs_info is reset to NULL. [1]. I think that is ok since the fs_info would have already been copied to the super block. [2] See sget_fc(): [1] https://github.com/torvalds/linux/blob/v6.12-rc4/fs/super.c#L774 [2] https://github.com/torvalds/linux/blob/v6.12-rc4/fs/super.c#L766 --Kalesh > > > + > > sync_filesystem(sb); > > /* structure copy of new mount options to sb */ > > *sb_opts = *new_opts; > > FWIW doing this as a structure copy was probably a terrible choice on my > part. :( > > > @@ -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) >
