[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);
}
}