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
......@@ -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)
......
......@@ -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);
......
......@@ -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,
......
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