Zizhi Wo <wozizhi@xxxxxxxxxx> wrote:
> 在 2024/10/10 19:26, David Howells 写道:
> > Zizhi Wo <wozizhi@xxxxxxxxxx> wrote:
> >
> >> + spin_lock(&object->lock);
> >> if (object->file) {
> >> fput(object->file);
> >> object->file = NULL;
> >> }
> >> + spin_unlock(&object->lock);
> > I would suggest stashing the file pointer in a local var and then doing the
> > fput() outside of the locks.
> > David
> >
>
> If fput() is executed outside the lock, I am currently unsure how to
> guarantee that file in __cachefiles_write() does not trigger null
> pointer dereference...
I'm not sure why there's a problem here. I was thinking along the lines of:
struct file *tmp;
spin_lock(&object->lock);
tmp = object->file)
object->file = NULL;
spin_unlock(&object->lock);
if (tmp)
fput(tmp);
Note that fput() may defer the actual work if the counter hits zero, so the
cleanup may not happen inside the lock; further, the cleanup done by __fput()
may sleep.
David
