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fuse: clean up device cloning

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- fuse_mutex is not needed for device cloning, because fuse_dev_install()
   uses cmpxcg() to set fud->fc, which prevents races between clone/mount
   or clone/clone.  This makes the logic simpler

 - Drop fc->dev_count.  This is only used to check in release if the device
   is the last clone, but checking list_empty(&fc->devices) is equivalent
   after removing the released device from the list.  Removing the fuse_dev
   before calling fuse_abort_conn() is okay, since the processing and io
   lists are now empty for this device.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Miklos Szeredi
2026-03-12 12:19:10 +01:00
parent d42eb23b2e
commit 4ae404afd9
3 changed files with 15 additions and 24 deletions
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35
fs/fuse/dev.c
View File

@@ -2547,6 +2547,7 @@ int fuse_dev_release(struct inode *inode, struct file *file)
struct fuse_pqueue *fpq = &fud->pq;
LIST_HEAD(to_end);
unsigned int i;
bool last;
spin_lock(&fpq->lock);
WARN_ON(!list_empty(&fpq->io));
@@ -2556,14 +2557,16 @@ int fuse_dev_release(struct inode *inode, struct file *file)
fuse_dev_end_requests(&to_end);
spin_lock(&fc->lock);
list_del(&fud->entry);
/* Are we the last open device? */
if (atomic_dec_and_test(&fc->dev_count)) {
last = list_empty(&fc->devices);
spin_unlock(&fc->lock);
if (last) {
WARN_ON(fc->iq.fasync != NULL);
fuse_abort_conn(fc);
}
spin_lock(&fc->lock);
list_del(&fud->entry);
spin_unlock(&fc->lock);
fuse_conn_put(fc);
}
fuse_dev_put(fud);
@@ -2582,23 +2585,10 @@ static int fuse_dev_fasync(int fd, struct file *file, int on)
return fasync_helper(fd, file, on, &fud->fc->iq.fasync);
}
static int fuse_device_clone(struct fuse_conn *fc, struct file *new)
{
struct fuse_dev *new_fud = fuse_file_to_fud(new);
if (fuse_dev_fc_get(new_fud))
return -EINVAL;
fuse_dev_install(new_fud, fc);
atomic_inc(&fc->dev_count);
return 0;
}
static long fuse_dev_ioctl_clone(struct file *file, __u32 __user *argp)
{
int oldfd;
struct fuse_dev *fud;
struct fuse_dev *fud, *new_fud;
if (get_user(oldfd, argp))
return -EFAULT;
@@ -2618,8 +2608,13 @@ static long fuse_dev_ioctl_clone(struct file *file, __u32 __user *argp)
if (IS_ERR(fud))
return PTR_ERR(fud);
guard(mutex)(&fuse_mutex);
return fuse_device_clone(fud->fc, file);
new_fud = fuse_file_to_fud(file);
if (fuse_dev_fc_get(new_fud))
return -EINVAL;
fuse_dev_install(new_fud, fud->fc);
return 0;
}
static long fuse_dev_ioctl_backing_open(struct file *file,

3
fs/fuse/fuse_i.h
View File

@@ -650,9 +650,6 @@ struct fuse_conn {
/** Refcount */
refcount_t count;
/** Number of fuse_dev's */
atomic_t dev_count;
/** Current epoch for up-to-date dentries */
atomic_t epoch;

1
fs/fuse/inode.c
View File

@@ -1001,7 +1001,6 @@ void fuse_conn_init(struct fuse_conn *fc, struct fuse_mount *fm,
spin_lock_init(&fc->bg_lock);
init_rwsem(&fc->killsb);
refcount_set(&fc->count, 1);
atomic_set(&fc->dev_count, 1);
atomic_set(&fc->epoch, 1);
INIT_WORK(&fc->epoch_work, fuse_epoch_work);
init_waitqueue_head(&fc->blocked_waitq);