diff options
| author | Sebastian Andrzej Siewior <bigeasy@linutronix.de> | 2022-07-27 14:49:04 +0300 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2022-07-30 07:38:16 +0300 |
| commit | 50417d22d0efbb1be76c3cb66b2329f83741c9c7 (patch) | |
| tree | dd7343e3ad9bd71c6e1e110f369e36e4437f236a | |
| parent | 45f78b0a2743c4fd71b73400bd5d5339628bf538 (diff) | |
| download | linux-50417d22d0efbb1be76c3cb66b2329f83741c9c7.tar.xz | |
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 <bigeasy@linutronix.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| -rw-r--r-- | fs/dcache.c | 10 |
1 files changed, 5 insertions, 5 deletions
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); |