Unverified Commit e7c8dde3 authored by Christian Brauner's avatar Christian Brauner
Browse files

fs: simplify rwlock to spinlock 

We're not taking the read_lock() anymore now that all lookup is
lockless. Just use a simple spinlock.

Link: https://lore.kernel.org/r/20241213-work-mount-rbtree-lockless-v3-6-6e3cdaf9b280@kernel.org


Reviewed-by: default avatarJeff Layton <jlayton@kernel.org>
Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent 4368898b

fs/namespace.c

+6 −9
Original line number Diff line number Diff line
@@ -78,8 +78,7 @@ static struct kmem_cache *mnt_cache __ro_after_init; 
static DECLARE_RWSEM(namespace_sem);

static HLIST_HEAD(unmounted);	/* protected by namespace_sem */

static LIST_HEAD(ex_mountpoints); /* protected by namespace_sem */

static DEFINE_RWLOCK(mnt_ns_tree_lock);

static seqcount_rwlock_t mnt_ns_tree_seqcount = SEQCNT_RWLOCK_ZERO(mnt_ns_tree_seqcount, &mnt_ns_tree_lock);

static DEFINE_SEQLOCK(mnt_ns_tree_lock);



static struct rb_root mnt_ns_tree = RB_ROOT; /* protected by mnt_ns_tree_lock */

static LIST_HEAD(mnt_ns_list); /* protected by mnt_ns_tree_lock */
@@ -131,14 +130,12 @@ static int mnt_ns_cmp(struct rb_node *a, const struct rb_node *b) 


static inline void mnt_ns_tree_write_lock(void)

{

	write_lock(&mnt_ns_tree_lock);

	write_seqcount_begin(&mnt_ns_tree_seqcount);

	write_seqlock(&mnt_ns_tree_lock);

}



static inline void mnt_ns_tree_write_unlock(void)

{

	write_seqcount_end(&mnt_ns_tree_seqcount);

	write_unlock(&mnt_ns_tree_lock);

	write_sequnlock(&mnt_ns_tree_lock);

}



static void mnt_ns_tree_add(struct mnt_namespace *ns)
@@ -163,7 +160,7 @@ static void mnt_ns_tree_add(struct mnt_namespace *ns) 


static void mnt_ns_release(struct mnt_namespace *ns)

{

	lockdep_assert_not_held(&mnt_ns_tree_lock);

	lockdep_assert_not_held(&mnt_ns_tree_lock.lock);



	/* keep alive for {list,stat}mount() */

	if (refcount_dec_and_test(&ns->passive)) {
@@ -225,11 +222,11 @@ static struct mnt_namespace *lookup_mnt_ns(u64 mnt_ns_id) 


	guard(rcu)();

	do {

		seq = read_seqcount_begin(&mnt_ns_tree_seqcount);

		seq = read_seqbegin(&mnt_ns_tree_lock);

		node = rb_find_rcu(&mnt_ns_id, &mnt_ns_tree, mnt_ns_find);

		if (node)

			break;

	} while (read_seqcount_retry(&mnt_ns_tree_seqcount, seq));

	} while (read_seqretry(&mnt_ns_tree_lock, seq));



	if (!node)

		return NULL;