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Commit 7ffdea7e authored by Al Viro's avatar Al Viro Committed by Eric Van Hensbergen
Browse files

locking in fs/9p ->readdir() 



	... is really excessive.  First of all, ->readdir() is serialized by
file->f_path.dentry->d_inode->i_mutex; playing with file->f_path.dentry->d_lock
is not buying you anything.  Moreover, rdir->mutex is pointless for exactly
the same reason - you'll never see contention on it.

	While we are at it, there's no point in having rdir->buf a pointer -
you have it point just past the end of rdir, so it might as well be a flex
array (and no, it's not a gccism).

	Absolutely untested patch follows:

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarEric Van Hensbergen <ericvh@gmail.com>
parent 836dc9e3

fs/9p/vfs_dir.c

+23 −69
Original line number Diff line number Diff line
@@ -52,10 +52,9 @@ 
 */



struct p9_rdir {

	struct mutex mutex;

	int head;

	int tail;

	uint8_t *buf;

	uint8_t buf[];

};



/**
@@ -93,33 +92,12 @@ static void p9stat_init(struct p9_wstat *stbuf) 
 *

 */



static int v9fs_alloc_rdir_buf(struct file *filp, int buflen)

static struct p9_rdir *v9fs_alloc_rdir_buf(struct file *filp, int buflen)

{

	struct p9_rdir *rdir;

	struct p9_fid *fid;

	int err = 0;



	fid = filp->private_data;

	if (!fid->rdir) {

		rdir = kmalloc(sizeof(struct p9_rdir) + buflen, GFP_KERNEL);



		if (rdir == NULL) {

			err = -ENOMEM;

			goto exit;

		}

		spin_lock(&filp->f_dentry->d_lock);

		if (!fid->rdir) {

			rdir->buf = (uint8_t *)rdir + sizeof(struct p9_rdir);

			mutex_init(&rdir->mutex);

			rdir->head = rdir->tail = 0;

			fid->rdir = (void *) rdir;

			rdir = NULL;

		}

		spin_unlock(&filp->f_dentry->d_lock);

		kfree(rdir);

	}

exit:

	return err;

	struct p9_fid *fid = filp->private_data;

	if (!fid->rdir)

		fid->rdir = kzalloc(sizeof(struct p9_rdir) + buflen, GFP_KERNEL);

	return fid->rdir;

}



/**
@@ -145,20 +123,16 @@ static int v9fs_dir_readdir(struct file *filp, void *dirent, filldir_t filldir) 


	buflen = fid->clnt->msize - P9_IOHDRSZ;



	err = v9fs_alloc_rdir_buf(filp, buflen);

	if (err)

		goto exit;

	rdir = (struct p9_rdir *) fid->rdir;

	rdir = v9fs_alloc_rdir_buf(filp, buflen);

	if (!rdir)

		return -ENOMEM;



	err = mutex_lock_interruptible(&rdir->mutex);

	if (err)

		return err;

	while (err == 0) {

	while (1) {

		if (rdir->tail == rdir->head) {

			err = v9fs_file_readn(filp, rdir->buf, NULL,

							buflen, filp->f_pos);

			if (err <= 0)

				goto unlock_and_exit;

				return err;



			rdir->head = 0;

			rdir->tail = err;
@@ -169,9 +143,8 @@ static int v9fs_dir_readdir(struct file *filp, void *dirent, filldir_t filldir) 
					  rdir->tail - rdir->head, &st);

			if (err) {

				p9_debug(P9_DEBUG_VFS, "returned %d\n", err);

				err = -EIO;

				p9stat_free(&st);

				goto unlock_and_exit;

				return -EIO;

			}

			reclen = st.size+2;
@@ -180,19 +153,13 @@ static int v9fs_dir_readdir(struct file *filp, void *dirent, filldir_t filldir) 


			p9stat_free(&st);



			if (over) {

				err = 0;

				goto unlock_and_exit;

			}

			if (over)

				return 0;



			rdir->head += reclen;

			filp->f_pos += reclen;

		}

	}



unlock_and_exit:

	mutex_unlock(&rdir->mutex);

exit:

	return err;

}



/**
@@ -218,21 +185,16 @@ static int v9fs_dir_readdir_dotl(struct file *filp, void *dirent, 


	buflen = fid->clnt->msize - P9_READDIRHDRSZ;



	err = v9fs_alloc_rdir_buf(filp, buflen);

	if (err)

		goto exit;

	rdir = (struct p9_rdir *) fid->rdir;



	err = mutex_lock_interruptible(&rdir->mutex);

	if (err)

		return err;

	rdir = v9fs_alloc_rdir_buf(filp, buflen);

	if (!rdir)

		return -ENOMEM;



	while (err == 0) {

	while (1) {

		if (rdir->tail == rdir->head) {

			err = p9_client_readdir(fid, rdir->buf, buflen,

						filp->f_pos);

			if (err <= 0)

				goto unlock_and_exit;

				return err;



			rdir->head = 0;

			rdir->tail = err;
@@ -245,8 +207,7 @@ static int v9fs_dir_readdir_dotl(struct file *filp, void *dirent, 
					    &curdirent);

			if (err < 0) {

				p9_debug(P9_DEBUG_VFS, "returned %d\n", err);

				err = -EIO;

				goto unlock_and_exit;

				return -EIO;

			}



			/* d_off in dirent structure tracks the offset into
@@ -261,20 +222,13 @@ static int v9fs_dir_readdir_dotl(struct file *filp, void *dirent, 
					curdirent.d_type);

			oldoffset = curdirent.d_off;



			if (over) {

				err = 0;

				goto unlock_and_exit;

			}

			if (over)

				return 0;



			filp->f_pos = curdirent.d_off;

			rdir->head += err;

		}

	}



unlock_and_exit:

	mutex_unlock(&rdir->mutex);

exit:

	return err;

}