From 50417d22d0efbb1be76c3cb66b2329f83741c9c7 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Wed, 27 Jul 2022 13:49:04 +0200 Subject: fs/dcache: Move wakeup out of i_seq_dir write held region. __d_add() and __d_move() wake up waiters on dentry::d_wait from within the i_seq_dir write held region. This violates the PREEMPT_RT constraints as the wake up acquires wait_queue_head::lock which is a "sleeping" spinlock on RT. There is no requirement to do so. __d_lookup_unhash() has cleared DCACHE_PAR_LOOKUP and dentry::d_wait and returned the now unreachable wait queue head pointer to the caller, so the actual wake up can be postponed until the i_dir_seq write side critical section is left. The only requirement is that dentry::lock is held across the whole sequence including the wake up. The previous commit includes an analysis why this is considered safe. Move the wake up past end_dir_add() which leaves the i_dir_seq write side critical section and enables preemption. For non RT kernels there is no difference because preemption is still disabled due to dentry::lock being held, but it shortens the time between wake up and unlocking dentry::lock, which reduces the contention for the woken up waiter. Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Al Viro --- fs/dcache.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) (limited to 'fs/dcache.c') diff --git a/fs/dcache.c b/fs/dcache.c index b6cdc0ffca6f..ea5cdec24ea7 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -2581,11 +2581,13 @@ static inline unsigned start_dir_add(struct inode *dir) } } -static inline void end_dir_add(struct inode *dir, unsigned n) +static inline void end_dir_add(struct inode *dir, unsigned int n, + wait_queue_head_t *d_wait) { smp_store_release(&dir->i_dir_seq, n + 2); if (IS_ENABLED(CONFIG_PREEMPT_RT)) preempt_enable(); + wake_up_all(d_wait); } static void d_wait_lookup(struct dentry *dentry) @@ -2756,7 +2758,6 @@ static inline void __d_add(struct dentry *dentry, struct inode *inode) dir = dentry->d_parent->d_inode; n = start_dir_add(dir); d_wait = __d_lookup_unhash(dentry); - wake_up_all(d_wait); } if (inode) { unsigned add_flags = d_flags_for_inode(inode); @@ -2768,7 +2769,7 @@ static inline void __d_add(struct dentry *dentry, struct inode *inode) } __d_rehash(dentry); if (dir) - end_dir_add(dir, n); + end_dir_add(dir, n, d_wait); spin_unlock(&dentry->d_lock); if (inode) spin_unlock(&inode->i_lock); @@ -2947,7 +2948,6 @@ static void __d_move(struct dentry *dentry, struct dentry *target, dir = target->d_parent->d_inode; n = start_dir_add(dir); d_wait = __d_lookup_unhash(target); - wake_up_all(d_wait); } write_seqcount_begin(&dentry->d_seq); @@ -2983,7 +2983,7 @@ static void __d_move(struct dentry *dentry, struct dentry *target, write_seqcount_end(&dentry->d_seq); if (dir) - end_dir_add(dir, n); + end_dir_add(dir, n, d_wait); if (dentry->d_parent != old_parent) spin_unlock(&dentry->d_parent->d_lock); -- cgit v1.2.3