Commit 73ce8355 authored by Miklos Szeredi's avatar Miklos Szeredi
Browse files

[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: default avatarMiklos Szeredi <miklos@szeredi.hu>
parent 2514395e
......@@ -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);
}
}
......
......@@ -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);
/**
......
......@@ -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;
......
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