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Subject[34-longterm 140/247] fuse: fix hang of single threaded fuseblk filesystem
Date
From: Miklos Szeredi <mszeredi@suse.cz>

-------------------
This is a commit scheduled for the next v2.6.34 longterm release.
If you see a problem with using this for longterm, please comment.
-------------------
commit 5a18ec176c934ca1bc9dc61580a5e0e90a9b5733 upstream.

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>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
fs/fuse/file.c | 52 +++++++++++++++++++++++++++++++++++++++++++++-------
fs/fuse/fuse_i.h | 6 +++++-
2 files changed, 50 insertions(+), 8 deletions(-)
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index edfce0b..f6104a95 100644
--- 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)
@@ -549,7 +587,7 @@ static void fuse_readpages_end(struct fuse_conn *fc, struct fuse_req *req)
unlock_page(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)
@@ -1129,7 +1167,7 @@ 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 01cc462..e6d614d 100644
--- 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
@@ -254,7 +255,10 @@ struct fuse_req {
union {
struct fuse_forget_in forget_in;
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;
--
1.7.4.4


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