diff options
| author | Mateusz Guzik <mjguzik@gmail.com> | 2025-11-14 21:18:03 +0100 |
|---|---|---|
| committer | Christian Brauner <brauner@kernel.org> | 2025-11-19 14:49:28 +0100 |
| commit | bfef6e1f3488fc09ae966cb4dd2cb09f73cff791 (patch) | |
| tree | 181507c192c4c620407eae58e637a27e94c901fd | |
| parent | 6d228c181ed27957100bb1e77ccbb8078a22a8c1 (diff) | |
fs: move mntput_no_expire() slowpath into a dedicated routine
In the stock variant the compiler spills several registers on the stack
and employs stack smashing protection, adding even more code + a branch
on exit..
The actual fast path is small enough that the compiler inlines it for
all callers -- the symbol is no longer emitted.
Forcing noinline on it just for code-measurement purposes shows the fast
path dropping from 111 to 39 bytes.
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://patch.msgid.link/20251114201803.2183505-1-mjguzik@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
| -rw-r--r-- | fs/namespace.c | 38 |
1 files changed, 22 insertions, 16 deletions
diff --git a/fs/namespace.c b/fs/namespace.c index d82910f33dc4..43191f190ef6 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1345,26 +1345,12 @@ static void delayed_mntput(struct work_struct *unused) } static DECLARE_DELAYED_WORK(delayed_mntput_work, delayed_mntput); -static void mntput_no_expire(struct mount *mnt) +static void noinline mntput_no_expire_slowpath(struct mount *mnt) { LIST_HEAD(list); int count; - rcu_read_lock(); - if (likely(READ_ONCE(mnt->mnt_ns))) { - /* - * Since we don't do lock_mount_hash() here, - * ->mnt_ns can change under us. However, if it's - * non-NULL, then there's a reference that won't - * be dropped until after an RCU delay done after - * turning ->mnt_ns NULL. So if we observe it - * non-NULL under rcu_read_lock(), the reference - * we are dropping is not the final one. - */ - mnt_add_count(mnt, -1); - rcu_read_unlock(); - return; - } + VFS_BUG_ON(mnt->mnt_ns); lock_mount_hash(); /* * make sure that if __legitimize_mnt() has not seen us grab @@ -1415,6 +1401,26 @@ static void mntput_no_expire(struct mount *mnt) cleanup_mnt(mnt); } +static void mntput_no_expire(struct mount *mnt) +{ + rcu_read_lock(); + if (likely(READ_ONCE(mnt->mnt_ns))) { + /* + * Since we don't do lock_mount_hash() here, + * ->mnt_ns can change under us. However, if it's + * non-NULL, then there's a reference that won't + * be dropped until after an RCU delay done after + * turning ->mnt_ns NULL. So if we observe it + * non-NULL under rcu_read_lock(), the reference + * we are dropping is not the final one. + */ + mnt_add_count(mnt, -1); + rcu_read_unlock(); + return; + } + mntput_no_expire_slowpath(mnt); +} + void mntput(struct vfsmount *mnt) { if (mnt) { |