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Commit 48f5ec21 authored by Al Viro's avatar Al Viro
Browse files

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



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: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 232d2d60

fs/dcache.c

+31 −33
Original line number Diff line number Diff line
@@ -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;

	return !(seq & 1) && read_seqretry(lock, seq);

}

	} else			/* Odd */



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;