fuse: direct-io: don't dirty ITER_BVEC pages

commit 8fba54aebbdf1f999738121922e74bf796ad60ee upstream.

When reading from a loop device backed by a fuse file it deadlocks on
lock_page().

This is because the page is already locked by the read() operation done on
the loop device.  In this case we don't want to either lock the page or
dirty it.

So do what fs/direct-io.c does: only dirty the page for ITER_IOVEC vectors.

Reported-by: Sheng Yang <sheng@yasker.org>
Fixes: aa4d86163e4e ("block: loop: switch to VFS ITER_BVEC")
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Reviewed-by: Sheng Yang <sheng@yasker.org>
Reviewed-by: Ashish Samant <ashish.samant@oracle.com>
Tested-by: Sheng Yang <sheng@yasker.org>
Tested-by: Ashish Samant <ashish.samant@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index d58d4c0af0ce548bf7f24b6f71f32b6a2c2e96c0..682e79965c164663a94bac2c46b9303f21a1eba8 100644 (file)
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -540,13 +540,13 @@ void fuse_read_fill(struct fuse_req *req, struct file *file, loff_t pos,
        req->out.args[0].size = count;
 }
 
-static void fuse_release_user_pages(struct fuse_req *req, int write)
+static void fuse_release_user_pages(struct fuse_req *req, bool should_dirty)
 {
        unsigned i;
 
        for (i = 0; i < req->num_pages; i++) {
                struct page *page = req->pages[i];
-               if (write)
+               if (should_dirty)
                        set_page_dirty_lock(page);
                put_page(page);
        }
@@ -1331,6 +1331,7 @@ ssize_t fuse_direct_io(struct fuse_io_priv *io, struct iov_iter *iter,
                       loff_t *ppos, int flags)
 {
        int write = flags & FUSE_DIO_WRITE;
+       bool should_dirty = !write && iter_is_iovec(iter);
        int cuse = flags & FUSE_DIO_CUSE;
        struct file *file = io->file;
        struct inode *inode = file->f_mapping->host;
@@ -1375,7 +1376,7 @@ ssize_t fuse_direct_io(struct fuse_io_priv *io, struct iov_iter *iter,
                        nres = fuse_send_read(req, io, pos, nbytes, owner);
 
                if (!io->async)
-                       fuse_release_user_pages(req, !write);
+                       fuse_release_user_pages(req, should_dirty);
                if (req->out.h.error) {
                        if (!res)
                                res = req->out.h.error;