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split read_seqretry_or_unlock(), convert d_walk() to resulting primitives

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Separate "check if we need to retry" from "unlock if we are done and
had seq_writelock"; that allows to use these guys in d_walk(), where
we need to recheck every time we ascend back to parent, but do *not*
want to unlock until the very end.  Lift rcu_read_lock/rcu_read_unlock
out into callers.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2013-09-09 15:22:25 -04:00
parent 232d2d60aa
commit 48f5ec21d9
1 changed files with 31 additions and 33 deletions
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64
fs/dcache.c
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@ -100,30 +100,21 @@ static struct kmem_cache *dentry_cache __read_mostly;
*/
static inline void read_seqbegin_or_lock(seqlock_t *lock, int *seq)
{
if (!(*seq & 1)) { /* Even */
if (!(*seq & 1)) /* Even */
*seq = read_seqbegin(lock);
rcu_read_lock();
} else /* Odd */
else /* Odd */
write_seqlock(lock);
}
/**
* read_seqretry_or_unlock - end a seqretry or lock block & return retry status
* lock : sequence lock
* seq : sequence number
* Return: 1 to retry operation again, 0 to continue
*/
static inline int read_seqretry_or_unlock(seqlock_t *lock, int *seq)
static inline int need_seqretry(seqlock_t *lock, int seq)
{
if (!(*seq & 1)) { /* Even */
rcu_read_unlock();
if (read_seqretry(lock, *seq)) {
(*seq)++; /* Take writer lock */
return 1;
}
} else /* Odd */
return !(seq & 1) && read_seqretry(lock, seq);
}
static inline void done_seqretry(seqlock_t *lock, int seq)
{
if (seq & 1)
write_sequnlock(lock);
return 0;
}
/*
@ -1047,7 +1038,7 @@ void shrink_dcache_for_umount(struct super_block *sb)
* the parenthood after dropping the lock and check
* that the sequence number still matches.
*/
static struct dentry *try_to_ascend(struct dentry *old, int locked, unsigned seq)
static struct dentry *try_to_ascend(struct dentry *old, unsigned seq)
{
struct dentry *new = old->d_parent;
@ -1061,7 +1052,7 @@ static struct dentry *try_to_ascend(struct dentry *old, int locked, unsigned seq
*/
if (new != old->d_parent ||
(old->d_flags & DCACHE_DENTRY_KILLED) ||
(!locked && read_seqretry(&rename_lock, seq))) {
need_seqretry(&rename_lock, seq)) {
spin_unlock(&new->d_lock);
new = NULL;
}
@ -1098,13 +1089,12 @@ static void d_walk(struct dentry *parent, void *data,
{
struct dentry *this_parent;
struct list_head *next;
unsigned seq;
int locked = 0;
unsigned seq = 0;
enum d_walk_ret ret;
bool retry = true;
seq = read_seqbegin(&rename_lock);
again:
read_seqbegin_or_lock(&rename_lock, &seq);
this_parent = parent;
spin_lock(&this_parent->d_lock);
@ -1158,13 +1148,13 @@ static void d_walk(struct dentry *parent, void *data,
*/
if (this_parent != parent) {
struct dentry *child = this_parent;
this_parent = try_to_ascend(this_parent, locked, seq);
this_parent = try_to_ascend(this_parent, seq);
if (!this_parent)
goto rename_retry;
next = child->d_u.d_child.next;
goto resume;
}
if (!locked && read_seqretry(&rename_lock, seq)) {
if (need_seqretry(&rename_lock, seq)) {
spin_unlock(&this_parent->d_lock);
goto rename_retry;
}
@ -1173,17 +1163,13 @@ static void d_walk(struct dentry *parent, void *data,
out_unlock:
spin_unlock(&this_parent->d_lock);
if (locked)
write_sequnlock(&rename_lock);
done_seqretry(&rename_lock, seq);
return;
rename_retry:
if (!retry)
return;
if (locked)
goto again;
locked = 1;
write_seqlock(&rename_lock);
seq = 1;
goto again;
}
@ -2745,6 +2731,7 @@ static int prepend_path(const struct path *path,
char *bptr;
int blen;
rcu_read_lock();
restart:
bptr = *buffer;
blen = *buflen;
@ -2783,8 +2770,13 @@ static int prepend_path(const struct path *path,
dentry = parent;
}
if (read_seqretry_or_unlock(&rename_lock, &seq))
if (!(seq & 1))
rcu_read_unlock();
if (need_seqretry(&rename_lock, seq)) {
seq = 1;
goto restart;
}
done_seqretry(&rename_lock, seq);
if (error >= 0 && bptr == *buffer) {
if (--blen < 0)
@ -2957,6 +2949,7 @@ static char *__dentry_path(struct dentry *dentry, char *buf, int buflen)
int len, seq = 0;
int error = 0;
rcu_read_lock();
restart:
end = buf + buflen;
len = buflen;
@ -2979,8 +2972,13 @@ static char *__dentry_path(struct dentry *dentry, char *buf, int buflen)
retval = end;
dentry = parent;
}
if (read_seqretry_or_unlock(&rename_lock, &seq))
if (!(seq & 1))
rcu_read_unlock();
if (need_seqretry(&rename_lock, seq)) {
seq = 1;
goto restart;
}
done_seqretry(&rename_lock, seq);
if (error)
goto Elong;
return retval;