From 73ce8355c243a434524a34c05cc417dd0467996e Mon Sep 17 00:00:00 2001 From: Miklos Szeredi Date: Tue, 11 Apr 2006 21:14:26 +0200 Subject: [PATCH] [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 --- fs/fuse/dev.c | 28 ++++++++++++++++------------ fs/fuse/fuse_i.h | 12 +++--------- fs/fuse/inode.c | 27 +++++++++++++++++---------- 3 files changed, 36 insertions(+), 31 deletions(-) diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c index 6c740f8606..d4efb6223e 100644 --- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -120,20 +120,14 @@ void fuse_put_request(struct fuse_conn *fc, struct fuse_req *req) } } -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 @@ static void request_end(struct fuse_conn *fc, struct fuse_req *req) 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 19c7185a75..ee9b830425 100644 --- a/fs/fuse/fuse_i.h +++ b/fs/fuse/fuse_i.h @@ -255,15 +255,9 @@ struct fuse_conn { /** 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_noreply(struct fuse_conn *fc, struct fuse_req *req); 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 fd34037b05..43a6fc0db8 100644 --- a/fs/fuse/inode.c +++ b/fs/fuse/inode.c @@ -204,17 +204,26 @@ static void fuse_put_super(struct super_block *sb) { 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 @@ static struct fuse_conn *new_conn(void) 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 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent) goto err_free_req; sb->s_root = root_dentry; - fc->mounted = 1; fc->connected = 1; kobject_get(&fc->kobj); file->private_data = fc; -- 2.39.5