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fuse: writepages: crop secondary requests

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If writeback happens while fuse is in FUSE_NOWRITE condition, the request
will be queued but not processed immediately (see fuse_flush_writepages()).
Until FUSE_NOWRITE becomes relaxed, more writebacks can happen.  They will
be queued as "secondary" requests to that first ("primary") request.

Existing implementation crops only primary request.  This is not correct
because a subsequent extending write(2) may increase i_size and then
secondary requests won't be cropped properly.  The result would be stale
data written to the server to a file offset where zeros must be.

Similar problem may happen if secondary requests are attached to an
in-flight request that was already cropped.

The patch solves the issue by cropping all secondary requests in
fuse_writepage_end().  Thanks to Miklos for idea.

Signed-off-by: Maxim Patlasov <MPatlasov@parallels.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
This commit is contained in:
Maxim Patlasov 2013-10-02 21:38:32 +04:00 committed by Miklos Szeredi
parent f6011081f5
commit 6eaf4782eb
1 changed files with 31 additions and 5 deletions
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36
fs/fuse/file.c
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@ -1436,12 +1436,12 @@ static void fuse_writepage_finish(struct fuse_conn *fc, struct fuse_req *req)
}
/* Called under fc->lock, may release and reacquire it */
static void fuse_send_writepage(struct fuse_conn *fc, struct fuse_req *req)
static void fuse_send_writepage(struct fuse_conn *fc, struct fuse_req *req,
loff_t size)
__releases(fc->lock)
__acquires(fc->lock)
{
struct fuse_inode *fi = get_fuse_inode(req->inode);
loff_t size = i_size_read(req->inode);
struct fuse_write_in *inarg = &req->misc.write.in;
__u64 data_size = req->num_pages * PAGE_CACHE_SIZE;
@ -1482,12 +1482,13 @@ __acquires(fc->lock)
{
struct fuse_conn *fc = get_fuse_conn(inode);
struct fuse_inode *fi = get_fuse_inode(inode);
size_t crop = i_size_read(inode);
struct fuse_req *req;
while (fi->writectr >= 0 && !list_empty(&fi->queued_writes)) {
req = list_entry(fi->queued_writes.next, struct fuse_req, list);
list_del_init(&req->list);
fuse_send_writepage(fc, req);
fuse_send_writepage(fc, req, crop);
}
}
@ -1499,12 +1500,37 @@ static void fuse_writepage_end(struct fuse_conn *fc, struct fuse_req *req)
mapping_set_error(inode->i_mapping, req->out.h.error);
spin_lock(&fc->lock);
while (req->misc.write.next) {
struct fuse_conn *fc = get_fuse_conn(inode);
struct fuse_write_in *inarg = &req->misc.write.in;
struct fuse_req *next = req->misc.write.next;
req->misc.write.next = next->misc.write.next;
next->misc.write.next = NULL;
list_add(&next->writepages_entry, &fi->writepages);
list_add_tail(&next->list, &fi->queued_writes);
fuse_flush_writepages(inode);
/*
* Skip fuse_flush_writepages() to make it easy to crop requests
* based on primary request size.
*
* 1st case (trivial): there are no concurrent activities using
* fuse_set/release_nowrite. Then we're on safe side because
* fuse_flush_writepages() would call fuse_send_writepage()
* anyway.
*
* 2nd case: someone called fuse_set_nowrite and it is waiting
* now for completion of all in-flight requests. This happens
* rarely and no more than once per page, so this should be
* okay.
*
* 3rd case: someone (e.g. fuse_do_setattr()) is in the middle
* of fuse_set_nowrite..fuse_release_nowrite section. The fact
* that fuse_set_nowrite returned implies that all in-flight
* requests were completed along with all of their secondary
* requests. Further primary requests are blocked by negative
* writectr. Hence there cannot be any in-flight requests and
* no invocations of fuse_writepage_end() while we're in
* fuse_set_nowrite..fuse_release_nowrite section.
*/
fuse_send_writepage(fc, next, inarg->offset + inarg->size);
}
fi->writectr--;
fuse_writepage_finish(fc, req);