@@ -2581,11 +2581,13 @@ static inline unsigned start_dir_add(str
}
}
-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
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
}
__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 *dent
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 *dent
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);
__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 <bigeasy@linutronix.de> --- fs/dcache.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)