Re: [syzbot] WARNING in mntput_no_expire (2)
From: Al Viro
Date: Mon Apr 05 2021 - 14:24:23 EST
On Mon, Apr 05, 2021 at 07:08:01PM +0200, Christian Brauner wrote:
> Ah dentry count of -127 looks... odd.
dead + 1...
void lockref_mark_dead(struct lockref *lockref)
{
assert_spin_locked(&lockref->lock);
lockref->count = -128;
}
IOW, a leaked (uncounted) reference to dentry, that got dget() called on
it after dentry had been freed.
IOW, current->fs->pwd.dentry happens to point to an already freed
struct dentry here. Joy...
Could you slap
spin_lock(¤t->fs->lock);
WARN_ON(d_count(current->fs->pwd.dentry) < 0);
spin_unlock(¤t->fs->lock);
before and after calls of io_issue_sqe() and see if it triggers? We definitely
are seeing buggered dentry refcounting here.