github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-05-23 06:31:58 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph

mount: add a comment about concurrent changes with statmount()/listmount()

Browse Source 
Add some comments in there highlighting a few non-obvious assumptions.

Link: https://lore.kernel.org/20250416-zerknirschen-aluminium-14a55639076f@brauner
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2025-04-16 10:19:05 +02:00
parent 0af2f6be1b
commit a68cb18624
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
1 changed files with 23 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
fs/namespace.c
View File

@ -5831,13 +5831,29 @@ static int do_statmount(struct kstatmount *s, u64 mnt_id, u64 mnt_ns_id,
return err;
s->root = root;
s->idmap = mnt_idmap(s->mnt);
if (s->mask & STATMOUNT_SB_BASIC)
statmount_sb_basic(s);
/*
* Note that mount properties in mnt->mnt_flags, mnt->mnt_idmap
* can change concurrently as we only hold the read-side of the
* namespace semaphore and mount properties may change with only
* the mount lock held.
*
* We could sample the mount lock sequence counter to detect
* those changes and retry. But it's not worth it. Worst that
* happens is that the mnt->mnt_idmap pointer is already changed
* while mnt->mnt_flags isn't or vica versa. So what.
*
* Both mnt->mnt_flags and mnt->mnt_idmap are set and retrieved
* via READ_ONCE()/WRITE_ONCE() and guard against theoretical
* torn read/write. That's all we care about right now.
*/
s->idmap = mnt_idmap(s->mnt);
if (s->mask & STATMOUNT_MNT_BASIC)
statmount_mnt_basic(s);
if (s->mask & STATMOUNT_SB_BASIC)
statmount_sb_basic(s);
if (s->mask & STATMOUNT_PROPAGATE_FROM)
statmount_propagate_from(s);
@ -6149,6 +6165,10 @@ SYSCALL_DEFINE4(listmount, const struct mnt_id_req __user *, req,
!ns_capable_noaudit(ns->user_ns, CAP_SYS_ADMIN))
return -ENOENT;
/*
* We only need to guard against mount topology changes as
* listmount() doesn't care about any mount properties.
*/
scoped_guard(rwsem_read, &namespace_sem)
ret = do_listmount(ns, kreq.mnt_id, last_mnt_id, kmnt_ids,
nr_mnt_ids, (flags & LISTMOUNT_REVERSE));