fuse: fix hang of single threaded fuseblk filesystem

Single threaded NTFS-3G could get stuck if a delayed RELEASE reply
triggered a DESTROY request via path_put().

Fix this by

 a) making RELEASE requests synchronous, whenever possible, on fuseblk
 filesystems

 b) if not possible (triggered by an asynchronous read/write) then do
 the path_put() in a separate thread with schedule_work().

Reported-by: Oliver Neukum <oneukum@suse.de>
Cc: stable@kernel.org
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 95da1bc1c8267a78efce954c56e7f48eb1338d42..9e0832dbb1e3dfb8e0872273fc53800f60a9251d 100644 (file)
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -86,18 +86,52 @@ struct fuse_file *fuse_file_get(struct fuse_file *ff)
        return ff;
 }
 
+static void fuse_release_async(struct work_struct *work)
+{
+       struct fuse_req *req;
+       struct fuse_conn *fc;
+       struct path path;
+
+       req = container_of(work, struct fuse_req, misc.release.work);
+       path = req->misc.release.path;
+       fc = get_fuse_conn(path.dentry->d_inode);
+
+       fuse_put_request(fc, req);
+       path_put(&path);
+}
+
 static void fuse_release_end(struct fuse_conn *fc, struct fuse_req *req)
 {
-       path_put(&req->misc.release.path);
+       if (fc->destroy_req) {
+               /*
+                * If this is a fuseblk mount, then it's possible that
+                * releasing the path will result in releasing the
+                * super block and sending the DESTROY request.  If
+                * the server is single threaded, this would hang.
+                * For this reason do the path_put() in a separate
+                * thread.
+                */
+               atomic_inc(&req->count);
+               INIT_WORK(&req->misc.release.work, fuse_release_async);
+               schedule_work(&req->misc.release.work);
+       } else {
+               path_put(&req->misc.release.path);
+       }
 }
 
-static void fuse_file_put(struct fuse_file *ff)
+static void fuse_file_put(struct fuse_file *ff, bool sync)
 {
        if (atomic_dec_and_test(&ff->count)) {
                struct fuse_req *req = ff->reserved_req;
 
-               req->end = fuse_release_end;
-               fuse_request_send_background(ff->fc, req);
+               if (sync) {
+                       fuse_request_send(ff->fc, req);
+                       path_put(&req->misc.release.path);
+                       fuse_put_request(ff->fc, req);
+               } else {
+                       req->end = fuse_release_end;
+                       fuse_request_send_background(ff->fc, req);
+               }
                kfree(ff);
        }
 }
@@ -219,8 +253,12 @@ void fuse_release_common(struct file *file, int opcode)
         * Normally this will send the RELEASE request, however if
         * some asynchronous READ or WRITE requests are outstanding,
         * the sending will be delayed.
+        *
+        * Make the release synchronous if this is a fuseblk mount,
+        * synchronous RELEASE is allowed (and desirable) in this case
+        * because the server can be trusted not to screw up.
         */
-       fuse_file_put(ff);
+       fuse_file_put(ff, ff->fc->destroy_req != NULL);
 }
 
 static int fuse_open(struct inode *inode, struct file *file)
@@ -558,7 +596,7 @@ static void fuse_readpages_end(struct fuse_conn *fc, struct fuse_req *req)
                page_cache_release(page);
        }
        if (req->ff)
-               fuse_file_put(req->ff);
+               fuse_file_put(req->ff, false);
 }
 
 static void fuse_send_readpages(struct fuse_req *req, struct file *file)
@@ -1137,7 +1175,7 @@ static ssize_t fuse_direct_write(struct file *file, const char __user *buf,
 static void fuse_writepage_free(struct fuse_conn *fc, struct fuse_req *req)
 {
        __free_page(req->pages[0]);
-       fuse_file_put(req->ff);
+       fuse_file_put(req->ff, false);
 }
 
 static void fuse_writepage_finish(struct fuse_conn *fc, struct fuse_req *req)

diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index ae5744a2f9e99a531551eb3704395d64ae08aee4..d4286947bc2cf57a6aba78109d3592ceb988205e 100644 (file)
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -21,6 +21,7 @@
 #include <linux/rwsem.h>
 #include <linux/rbtree.h>
 #include <linux/poll.h>
+#include <linux/workqueue.h>
 
 /** Max number of pages that can be used in a single read request */
 #define FUSE_MAX_PAGES_PER_REQ 32
@@ -262,7 +263,10 @@ struct fuse_req {
        /** Data for asynchronous requests */
        union {
                struct {
-                       struct fuse_release_in in;
+                       union {
+                               struct fuse_release_in in;
+                               struct work_struct work;
+                       };
                        struct path path;
                } release;
                struct fuse_init_in init_in;