On Thu, Dec 5, 2024 at 4:29 PM Jan Kara <jack@xxxxxxx> wrote: > On Thu 05-12-24 16:01:07, Mateusz Guzik wrote: > > Suppose the CPU reordered loads of the flag and the fd table. There is > > no ordering in which it can see both the old table and the unset flag. > > But I disagree here. If the reads are reordered, then the fd table read can > happen during the "flag is true and the fd table is old" state and the flag > read can happen later in "flag is false and the fd table is new" state. > Just as I outlined above... In your example all the work happens *after* synchronize_rcu(). The thread resizing the table already published the result even before calling into it. Furthermore by the time synchronize_rcu returns everyone is guaranteed to have issued a full fence. Meaning nobody can see the flag as unset. -- Mateusz Guzik <mjguzik gmail.com>