On Sun, Jul 22, 2018 at 03:17:07PM +0200, Richard Weinberger wrote: > On Fri, Jul 20, 2018 at 2:54 AM, Theuns Verwoerd > <[email protected]> wrote: > > > > On 07/20/2018 12:04 PM, Al Viro wrote: > >> On Fri, Jul 20, 2018 at 11:50:12AM +1200, Theuns Verwoerd wrote: > >> > >>> +ssize_t jffs2_sync_file_read(struct file *f, > >>> + char __user *b, size_t len, loff_t *ofs) > >>> +{ > >>> + struct jffs2_sb_info *c = file_inode(f)->i_private; > >>> + > >>> + while (c->tidemark) > >>> + schedule(); > >>> + > >>> + return 0; > >>> +} > >> Brilliant. So when that gets called with c->tidemark being true and > >> need_resched() - false, we shall... > > By my reading, schedule() will happily force a reschedule (once) when > > need_resched() is false. Every time the process is granted a time > > slice, it'll check the condition and surrender if not ready.
Except that the task remains runnable (and not using its timeslice up). It won't sleep; there's nothing to drive it into TASK_NOT_RUNNING state. Try it and watch what's going on when you trigger that loop. That's really not a good way to wait for something to happen.
