UBIFS: possible bug for the absence of memory barrier

[Adrian Hunter]

홍신 shin hong wrote:
> Hello. I am reporting the possible bugs caused by absence of memory barriers.
> 
> Since I do not have much background,
> I can not convince that the codes are buggy.
> But I hope that this report is helpful.
> Please examine the issue and let me know your opinion.
> 
> In add_replay_bud() of UBIFS in Linux 2.6.30.5, it newly allocate a bud_entry
> object and initialize and then link it to the replay_buds list.
> 
> The last initialization operation is "b->sqnum = sqnum ;" and
> the linking to the list "list_add_tail(&b->list, &c->replay_buds;".
> 
> However, since there is no memory barrier between these two,
> the execution order might be changed
> so that uninitialized data might be accessible to other threads.
> 
> Therefore, race condition might occur and it may result error.
> 
> Please examine this issue.
> Thank you
> 
> Sincerely
> Shin Hong

A race is not possible because there is only one thread that can be
replaying because it is only done when mounting.