Hello! We were pondering with Amir about some issues with fsnotify subsystem and as a building block we would need a mechanism to make sure write(2) has completed. For simplicity we could imagine it like a sequence write(2) START do stuff to perform write END and we need a mechanism to wait for all processes that already passed START to reach END. Ideally without blocking new writes while we wait for the pending ones. Now this seems like a good task for SRCU. We could do: write(2) srcu_read_lock(&sb->s_write_rcu); do stuff to perform write srcu_read_unlock(&sb->s_write_rcu); and use synchronize_srcu(&sb->s_write_rcu) for waiting. But the trouble with writes is there are things like aio or io_uring where the part with srcu_read_lock() happens from one task (the submitter) while the part with srcu_read_unlock() happens from another context (usually worker thread triggered by IRQ reporting that the HW has finished the IO). Is there any chance to make SRCU work in a situation like this? It seems to me in principle it should be possible to make this work but maybe there are some implementation constraints I'm missing... Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
