Hello! On Sun 25-06-23 15:56:10, Baokun Li wrote: > > > I think we can simply focus on the race between the DQ_ACTIVE_B flag and > > > the DQ_MOD_B flag, which is the core problem, because the same quota > > > should not have both flags. These two flags are protected by dq_list_lock > > > and dquot->dq_lock respectively, so it makes sense to add a > > > wait_on_dquot() to ensure the accuracy of DQ_ACTIVE_B. > > But the fundamental problem is not only the race with DQ_MOD_B setting. The > > dquot structure can be completely freed by the time > > dquot_claim_space_nodirty() calls dquot_mark_dquot_dirty() on it. That's > > why I think making __dquot_transfer() obey dquot_srcu rules is the right > > solution. > Yes, now I also think that making __dquot_transfer() obey dquot_srcu > rules is a better solution. But with inode->i_lock protection, why would > the dquot structure be completely freed? Well, when dquot_claim_space_nodirty() calls mark_all_dquot_dirty() it does not hold any locks (only dquot_srcu). So nothing prevents dquot_transfer() to go, swap dquot structure pointers and drop dquot references and after that mark_all_dquot_dirty() can use a stale pointer to call mark_dquot_dirty() on already freed memory. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
