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Commit 58db63d0 authored by Nick Piggin's avatar Nick Piggin
Browse files

fs: dcache avoid starvation in dcache multi-step operations 



Long lived dcache "multi-step" operations which retry on rename seq can
be starved with a lot of rename activity. If they fail after the 1st pass,
take the rename_lock for writing to avoid further starvation.

Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
parent b5c84bf6

fs/dcache.c

+42 −14
Original line number Diff line number Diff line
@@ -973,10 +973,11 @@ int have_submounts(struct dentry *parent) 
	struct dentry *this_parent;

	struct list_head *next;

	unsigned seq;

	int locked = 0;



rename_retry:

	this_parent = parent;

	seq = read_seqbegin(&rename_lock);

again:

	this_parent = parent;



	if (d_mountpoint(parent))

		goto positive;
@@ -1021,7 +1022,7 @@ int have_submounts(struct dentry *parent) 
		/* might go back up the wrong parent if we have had a rename

		 * or deletion */

		if (this_parent != child->d_parent ||

				read_seqretry(&rename_lock, seq)) {

			 (!locked && read_seqretry(&rename_lock, seq))) {

			spin_unlock(&this_parent->d_lock);

			rcu_read_unlock();

			goto rename_retry;
@@ -1031,13 +1032,22 @@ int have_submounts(struct dentry *parent) 
		goto resume;

	}

	spin_unlock(&this_parent->d_lock);

	if (read_seqretry(&rename_lock, seq))

	if (!locked && read_seqretry(&rename_lock, seq))

		goto rename_retry;

	if (locked)

		write_sequnlock(&rename_lock);

	return 0; /* No mount points found in tree */

positive:

	if (read_seqretry(&rename_lock, seq))

	if (!locked && read_seqretry(&rename_lock, seq))

		goto rename_retry;

	if (locked)

		write_sequnlock(&rename_lock);

	return 1;



rename_retry:

	locked = 1;

	write_seqlock(&rename_lock);

	goto again;

}

EXPORT_SYMBOL(have_submounts);
@@ -1061,11 +1071,11 @@ static int select_parent(struct dentry * parent) 
	struct list_head *next;

	unsigned seq;

	int found = 0;

	int locked = 0;



rename_retry:

	this_parent = parent;

	seq = read_seqbegin(&rename_lock);



again:

	this_parent = parent;

	spin_lock(&this_parent->d_lock);

repeat:

	next = this_parent->d_subdirs.next;
@@ -1127,7 +1137,7 @@ static int select_parent(struct dentry * parent) 
		/* might go back up the wrong parent if we have had a rename

		 * or deletion */

		if (this_parent != child->d_parent ||

				read_seqretry(&rename_lock, seq)) {

			(!locked && read_seqretry(&rename_lock, seq))) {

			spin_unlock(&this_parent->d_lock);

			rcu_read_unlock();

			goto rename_retry;
@@ -1138,9 +1148,18 @@ static int select_parent(struct dentry * parent) 
	}

out:

	spin_unlock(&this_parent->d_lock);

	if (read_seqretry(&rename_lock, seq))

	if (!locked && read_seqretry(&rename_lock, seq))

		goto rename_retry;

	if (locked)

		write_sequnlock(&rename_lock);

	return found;



rename_retry:

	if (found)

		return found;

	locked = 1;

	write_seqlock(&rename_lock);

	goto again;

}



/**
@@ -2655,10 +2674,11 @@ void d_genocide(struct dentry *root) 
	struct dentry *this_parent;

	struct list_head *next;

	unsigned seq;

	int locked = 0;



rename_retry:

	this_parent = root;

	seq = read_seqbegin(&rename_lock);

again:

	this_parent = root;

	spin_lock(&this_parent->d_lock);

repeat:

	next = this_parent->d_subdirs.next;
@@ -2703,7 +2723,7 @@ void d_genocide(struct dentry *root) 
		/* might go back up the wrong parent if we have had a rename

		 * or deletion */

		if (this_parent != child->d_parent ||

				read_seqretry(&rename_lock, seq)) {

			 (!locked && read_seqretry(&rename_lock, seq))) {

			spin_unlock(&this_parent->d_lock);

			rcu_read_unlock();

			goto rename_retry;
@@ -2713,8 +2733,16 @@ void d_genocide(struct dentry *root) 
		goto resume;

	}

	spin_unlock(&this_parent->d_lock);

	if (read_seqretry(&rename_lock, seq))

	if (!locked && read_seqretry(&rename_lock, seq))

		goto rename_retry;

	if (locked)

		write_sequnlock(&rename_lock);

	return;



rename_retry:

	locked = 1;

	write_seqlock(&rename_lock);

	goto again;

}



/**