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authorAl Viro <viro@zeniv.linux.org.uk>2019-07-24 23:01:55 -0400
committerAl Viro <viro@zeniv.linux.org.uk>2019-07-24 23:02:21 -0400
commitff09297ec9964b3fe4bade77c92c75fde34fa8e9 (patch)
tree145157267c90462a14ecaec483657d796a37e5d5 /fs/autofs
parent5f9e832c137075045d15cd6899ab0505cfb2ca4b (diff)
autofs: simplify get_next_positive_...(), get rid of trylocks
* new helper: positive_after(parent, child); parent->d_lock is held by caller, grabs and returns the first thing after child in the list of children that has simple_positive() true. NULL if nothing's found; NULL child == search the entire list. * get_next_positive_subdir() loses the redundant check for d_count and switches to use of that helper. BTW, dput(NULL) is a no-op for a good reason... * get_next_positive_dentry() switched to the same helper. Logics: look for positive child in prev; if not found, look for the positive child of prev's parent following prev, etc. That way we are guaranteed that we are only moving rootwards through the ancestors of prev, which is pinned and thus not going anywhere. Since ->d_parent on autofs never changes, the same goes for the entire chain of ancestors and we don't need overlapping ->d_lock on them. Which avoids the trylock loops, in addition to simplifying the logics in there... Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/autofs')
-rw-r--r--fs/autofs/expire.c103
1 files changed, 32 insertions, 71 deletions
diff --git a/fs/autofs/expire.c b/fs/autofs/expire.c
index cdff0567aacb..2866fabf497f 100644
--- a/fs/autofs/expire.c
+++ b/fs/autofs/expire.c
@@ -70,6 +70,27 @@ done:
return status;
}
+/* p->d_lock held */
+static struct dentry *positive_after(struct dentry *p, struct dentry *child)
+{
+ if (child)
+ child = list_next_entry(child, d_child);
+ else
+ child = list_first_entry(&p->d_subdirs, struct dentry, d_child);
+
+ list_for_each_entry_from(child, &p->d_subdirs, d_child) {
+ spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
+ if (simple_positive(child)) {
+ dget_dlock(child);
+ spin_unlock(&child->d_lock);
+ return child;
+ }
+ spin_unlock(&child->d_lock);
+ }
+
+ return NULL;
+}
+
/*
* Calculate and dget next entry in the subdirs list under root.
*/
@@ -77,43 +98,14 @@ static struct dentry *get_next_positive_subdir(struct dentry *prev,
struct dentry *root)
{
struct autofs_sb_info *sbi = autofs_sbi(root->d_sb);
- struct list_head *next;
struct dentry *q;
spin_lock(&sbi->lookup_lock);
spin_lock(&root->d_lock);
-
- if (prev)
- next = prev->d_child.next;
- else {
- prev = dget_dlock(root);
- next = prev->d_subdirs.next;
- }
-
-cont:
- if (next == &root->d_subdirs) {
- spin_unlock(&root->d_lock);
- spin_unlock(&sbi->lookup_lock);
- dput(prev);
- return NULL;
- }
-
- q = list_entry(next, struct dentry, d_child);
-
- spin_lock_nested(&q->d_lock, DENTRY_D_LOCK_NESTED);
- /* Already gone or negative dentry (under construction) - try next */
- if (!d_count(q) || !simple_positive(q)) {
- spin_unlock(&q->d_lock);
- next = q->d_child.next;
- goto cont;
- }
- dget_dlock(q);
- spin_unlock(&q->d_lock);
+ q = positive_after(root, prev);
spin_unlock(&root->d_lock);
spin_unlock(&sbi->lookup_lock);
-
dput(prev);
-
return q;
}
@@ -124,59 +116,28 @@ static struct dentry *get_next_positive_dentry(struct dentry *prev,
struct dentry *root)
{
struct autofs_sb_info *sbi = autofs_sbi(root->d_sb);
- struct list_head *next;
- struct dentry *p, *ret;
+ struct dentry *p = prev, *ret = NULL, *d = NULL;
if (prev == NULL)
return dget(root);
spin_lock(&sbi->lookup_lock);
-relock:
- p = prev;
spin_lock(&p->d_lock);
-again:
- next = p->d_subdirs.next;
- if (next == &p->d_subdirs) {
- while (1) {
- struct dentry *parent;
-
- if (p == root) {
- spin_unlock(&p->d_lock);
- spin_unlock(&sbi->lookup_lock);
- dput(prev);
- return NULL;
- }
+ while (1) {
+ struct dentry *parent;
- parent = p->d_parent;
- if (!spin_trylock(&parent->d_lock)) {
- spin_unlock(&p->d_lock);
- cpu_relax();
- goto relock;
- }
- spin_unlock(&p->d_lock);
- next = p->d_child.next;
- p = parent;
- if (next != &parent->d_subdirs)
- break;
- }
- }
- ret = list_entry(next, struct dentry, d_child);
-
- spin_lock_nested(&ret->d_lock, DENTRY_D_LOCK_NESTED);
- /* Negative dentry - try next */
- if (!simple_positive(ret)) {
+ ret = positive_after(p, d);
+ if (ret || p == root)
+ break;
+ parent = p->d_parent;
spin_unlock(&p->d_lock);
- lock_set_subclass(&ret->d_lock.dep_map, 0, _RET_IP_);
- p = ret;
- goto again;
+ spin_lock(&parent->d_lock);
+ d = p;
+ p = parent;
}
- dget_dlock(ret);
- spin_unlock(&ret->d_lock);
spin_unlock(&p->d_lock);
spin_unlock(&sbi->lookup_lock);
-
dput(prev);
-
return ret;
}