[fuse] fix deadlock between fuse_put_super() and request_end()
A deadlock was possible, when the last reference to the superblock was
held due to a background request containing a file reference.
Releasing the file would release the vfsmount which in turn would
release the superblock. Since sbput_sem is held during the fput() and
fuse_put_super() tries to acquire this same semaphore, a deadlock
results.
The chosen soltuion is to get rid of sbput_sem, and instead use the
spinlock to ensure the referenced inodes/file are released only once.
Since the actual release may sleep, defer these outside the locked
region, but using local variables instead of the structure members.
This is a much more rubust solution.
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 6c740f8..d4efb62 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -120,20 +120,14 @@
}
}
-void fuse_release_background(struct fuse_conn *fc, struct fuse_req *req)
+void fuse_remove_background(struct fuse_conn *fc, struct fuse_req *req)
{
- iput(req->inode);
- iput(req->inode2);
- if (req->file)
- fput(req->file);
- spin_lock(&fc->lock);
- list_del(&req->bg_entry);
+ list_del_init(&req->bg_entry);
if (fc->num_background == FUSE_MAX_BACKGROUND) {
fc->blocked = 0;
wake_up_all(&fc->blocked_waitq);
}
fc->num_background--;
- spin_unlock(&fc->lock);
}
/*
@@ -163,17 +157,27 @@
wake_up(&req->waitq);
fuse_put_request(fc, req);
} else {
+ struct inode *inode = req->inode;
+ struct inode *inode2 = req->inode2;
+ struct file *file = req->file;
void (*end) (struct fuse_conn *, struct fuse_req *) = req->end;
req->end = NULL;
+ req->inode = NULL;
+ req->inode2 = NULL;
+ req->file = NULL;
+ if (!list_empty(&req->bg_entry))
+ fuse_remove_background(fc, req);
spin_unlock(&fc->lock);
- down_read(&fc->sbput_sem);
- if (fc->mounted)
- fuse_release_background(fc, req);
- up_read(&fc->sbput_sem);
+
if (end)
end(fc, req);
else
fuse_put_request(fc, req);
+
+ if (file)
+ fput(file);
+ iput(inode);
+ iput(inode2);
}
}
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 19c7185..ee9b830 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -255,15 +255,9 @@
/** waitq for blocked connection */
wait_queue_head_t blocked_waitq;
- /** RW semaphore for exclusion with fuse_put_super() */
- struct rw_semaphore sbput_sem;
-
/** The next unique request id */
u64 reqctr;
- /** Mount is active */
- unsigned mounted;
-
/** Connection established, cleared on umount, connection
abort and device release */
unsigned connected;
@@ -474,11 +468,11 @@
void request_send_background(struct fuse_conn *fc, struct fuse_req *req);
/**
- * Release inodes and file associated with background request
+ * Remove request from the the background list
*/
-void fuse_release_background(struct fuse_conn *fc, struct fuse_req *req);
+void fuse_remove_background(struct fuse_conn *fc, struct fuse_req *req);
-/* Abort all requests */
+/** Abort all requests */
void fuse_abort_conn(struct fuse_conn *fc);
/**
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index fd34037..43a6fc0 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -204,17 +204,26 @@
{
struct fuse_conn *fc = get_fuse_conn_super(sb);
- down_write(&fc->sbput_sem);
- while (!list_empty(&fc->background))
- fuse_release_background(fc,
- list_entry(fc->background.next,
- struct fuse_req, bg_entry));
-
spin_lock(&fc->lock);
- fc->mounted = 0;
fc->connected = 0;
+ while (!list_empty(&fc->background)) {
+ struct fuse_req *req = list_entry(fc->background.next,
+ struct fuse_req, bg_entry);
+ struct inode *inode = req->inode;
+ struct inode *inode2 = req->inode2;
+
+ /* File would hold a reference to vfsmount */
+ BUG_ON(req->file);
+ req->inode = NULL;
+ req->inode2 = NULL;
+ fuse_remove_background(fc, req);
+
+ spin_unlock(&fc->lock);
+ iput(inode);
+ iput(inode2);
+ spin_lock(&fc->lock);
+ }
spin_unlock(&fc->lock);
- up_write(&fc->sbput_sem);
/* Flush all readers on this fs */
kill_fasync(&fc->fasync, SIGIO, POLL_IN);
wake_up_all(&fc->waitq);
@@ -386,7 +395,6 @@
INIT_LIST_HEAD(&fc->processing);
INIT_LIST_HEAD(&fc->io);
INIT_LIST_HEAD(&fc->background);
- init_rwsem(&fc->sbput_sem);
kobj_set_kset_s(fc, connections_subsys);
kobject_init(&fc->kobj);
atomic_set(&fc->num_waiting, 0);
@@ -541,7 +549,6 @@
goto err_free_req;
sb->s_root = root_dentry;
- fc->mounted = 1;
fc->connected = 1;
kobject_get(&fc->kobj);
file->private_data = fc;