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Commit ea8cd333 authored by Pavel Emelyanov's avatar Pavel Emelyanov Committed by Miklos Szeredi
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fuse: Fix O_DIRECT operations vs cached writeback misorder 



The problem is:

1. write cached data to a file
2. read directly from the same file (via another fd)

The 2nd operation may read stale data, i.e. the one that was in a file
before the 1st op. Problem is in how fuse manages writeback.

When direct op occurs the core kernel code calls filemap_write_and_wait
to flush all the cached ops in flight. But fuse acks the writeback right
after the ->writepages callback exits w/o waiting for the real write to
happen. Thus the subsequent direct op proceeds while the real writeback
is still in flight. This is a problem for backends that reorder operation.

Fix this by making the fuse direct IO callback explicitly wait on the
in-flight writeback to finish.

Signed-off-by: default avatarMaxim Patlasov <MPatlasov@parallels.com>
Signed-off-by: default avatarMiklos Szeredi <mszeredi@suse.cz>
parent fe38d7df

fs/fuse/cuse.c

+3 −2
Original line number Diff line number Diff line
@@ -95,7 +95,7 @@ static ssize_t cuse_read(struct file *file, char __user *buf, size_t count, 
	struct iovec iov = { .iov_base = buf, .iov_len = count };

	struct fuse_io_priv io = { .async = 0, .file = file };



	return fuse_direct_io(&io, &iov, 1, count, &pos, 0);

	return fuse_direct_io(&io, &iov, 1, count, &pos, FUSE_DIO_CUSE);

}



static ssize_t cuse_write(struct file *file, const char __user *buf,
@@ -109,7 +109,8 @@ static ssize_t cuse_write(struct file *file, const char __user *buf, 
	 * No locking or generic_write_checks(), the server is

	 * responsible for locking and sanity checks.

	 */

	return fuse_direct_io(&io, &iov, 1, count, &pos, 1);

	return fuse_direct_io(&io, &iov, 1, count, &pos,

			      FUSE_DIO_WRITE | FUSE_DIO_CUSE);

}



static int cuse_open(struct inode *inode, struct file *file)

fs/fuse/file.c

+26 −6
Original line number Diff line number Diff line
@@ -358,12 +358,13 @@ u64 fuse_lock_owner_id(struct fuse_conn *fc, fl_owner_t id) 
}



/*

 * Check if page is under writeback

 * Check if any page in a range is under writeback

 *

 * This is currently done by walking the list of writepage requests

 * for the inode, which can be pretty inefficient.

 */

static bool fuse_page_is_writeback(struct inode *inode, pgoff_t index)

static bool fuse_range_is_writeback(struct inode *inode, pgoff_t idx_from,

				   pgoff_t idx_to)

{

	struct fuse_conn *fc = get_fuse_conn(inode);

	struct fuse_inode *fi = get_fuse_inode(inode);
@@ -376,8 +377,8 @@ static bool fuse_page_is_writeback(struct inode *inode, pgoff_t index) 


		BUG_ON(req->inode != inode);

		curr_index = req->misc.write.in.offset >> PAGE_CACHE_SHIFT;

		if (curr_index <= index &&

		    index < curr_index + req->num_pages) {

		if (idx_from < curr_index + req->num_pages &&

		    curr_index <= idx_to) {

			found = true;

			break;

		}
@@ -387,6 +388,11 @@ static bool fuse_page_is_writeback(struct inode *inode, pgoff_t index) 
	return found;

}



static inline bool fuse_page_is_writeback(struct inode *inode, pgoff_t index)

{

	return fuse_range_is_writeback(inode, index, index);

}



/*

 * Wait for page writeback to be completed.

 *
@@ -1364,13 +1370,18 @@ static inline int fuse_iter_npages(const struct iov_iter *ii_p) 


ssize_t fuse_direct_io(struct fuse_io_priv *io, const struct iovec *iov,

		       unsigned long nr_segs, size_t count, loff_t *ppos,

		       int write)

		       int flags)

{

	int write = flags & FUSE_DIO_WRITE;

	int cuse = flags & FUSE_DIO_CUSE;

	struct file *file = io->file;

	struct inode *inode = file->f_mapping->host;

	struct fuse_file *ff = file->private_data;

	struct fuse_conn *fc = ff->fc;

	size_t nmax = write ? fc->max_write : fc->max_read;

	loff_t pos = *ppos;

	pgoff_t idx_from = pos >> PAGE_CACHE_SHIFT;

	pgoff_t idx_to = (pos + count - 1) >> PAGE_CACHE_SHIFT;

	ssize_t res = 0;

	struct fuse_req *req;

	struct iov_iter ii;
@@ -1384,6 +1395,14 @@ ssize_t fuse_direct_io(struct fuse_io_priv *io, const struct iovec *iov, 
	if (IS_ERR(req))

		return PTR_ERR(req);



	if (!cuse && fuse_range_is_writeback(inode, idx_from, idx_to)) {

		if (!write)

			mutex_lock(&inode->i_mutex);

		fuse_sync_writes(inode);

		if (!write)

			mutex_unlock(&inode->i_mutex);

	}



	while (count) {

		size_t nres;

		fl_owner_t owner = current->files;
@@ -1472,7 +1491,8 @@ static ssize_t __fuse_direct_write(struct fuse_io_priv *io, 


	res = generic_write_checks(file, ppos, &count, 0);

	if (!res)

		res = fuse_direct_io(io, iov, nr_segs, count, ppos, 1);

		res = fuse_direct_io(io, iov, nr_segs, count, ppos,

				     FUSE_DIO_WRITE);



	fuse_invalidate_attr(inode);

fs/fuse/fuse_i.h

+12 −1
Original line number Diff line number Diff line
@@ -868,9 +868,20 @@ int fuse_reverse_inval_entry(struct super_block *sb, u64 parent_nodeid, 


int fuse_do_open(struct fuse_conn *fc, u64 nodeid, struct file *file,

		 bool isdir);



/**

 * fuse_direct_io() flags

 */



/** If set, it is WRITE; otherwise - READ */

#define FUSE_DIO_WRITE (1 << 0)



/** CUSE pass fuse_direct_io() a file which f_mapping->host is not from FUSE */

#define FUSE_DIO_CUSE  (1 << 1)



ssize_t fuse_direct_io(struct fuse_io_priv *io, const struct iovec *iov,

		       unsigned long nr_segs, size_t count, loff_t *ppos,

		       int write);

		       int flags);

long fuse_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg,

		   unsigned int flags);

long fuse_ioctl_common(struct file *file, unsigned int cmd,