Hello, thanks a lot for help. I am sorry for the late response. I wanted to handle this mail with a clean head.
On Tue 2017-11-28 10:42:29, Byungchul Park wrote: > On Fri, Nov 24, 2017 at 04:58:16PM +0100, Petr Mladek wrote: > > @@ -1797,13 +1797,6 @@ asmlinkage int vprintk_emit(int facility, int level, > > spin_release(&console_owner_dep_map, 1, > > _THIS_IP_); > > printk_safe_exit_irqrestore(flags); > > > > - /* > > - * The owner passed the console lock to us. > > - * Since we did not spin on console lock, > > annotate > > - * this as a trylock. Otherwise lockdep will > > - * complain. > > - */ > > - mutex_acquire(&console_lock_dep_map, 0, 1, > > _THIS_IP_); > > Hello Petr, > > IMHO, it would get unbalanced if you only remove this mutex_acquire(). > > > console_unlock(); > > printk_safe_enter_irqsave(flags); > > } > > @@ -2334,10 +2327,10 @@ void console_unlock(void) > > /* The waiter is now free to continue */ > > spin_release(&console_owner_dep_map, 1, _THIS_IP_); > > /* > > - * Hand off console_lock to waiter. The waiter will perform > > - * the up(). After this, the waiter is the console_lock owner. > > + * Hand off console_lock to waiter. After this, the waiter > > + * is the console_lock owner. > > */ > > - mutex_release(&console_lock_dep_map, 1, _THIS_IP_); > > IMHO, this release() should be moved to somewhere properly. > > > + lock_commit_crosslock((struct lockdep_map > > *)&console_lock_dep_map); > > printk_safe_exit_irqrestore(flags); > > /* Note, if waiter is set, logbuf_lock is not held */ > > return; > > However, now that cross-release was introduces, lockdep can be applied > to semaphore operations. Actually, I have a plan to do that. I think it > would be better to make semaphore tracked with lockdep and remove all > these manual acquire() and release() here. What do you think about it? IMHO, it would be great to add lockdep annotations into semaphore operations. Well, I am not sure if this would be enough in this case. I think that the locking dependency in this Steven's patch is special. The semaphore is passed from one owner to another one without unlocking. Both sides wait for each other using a busy loop. The busy loop/waiting is activated only when the current owner is not sleeping to avoid softlockup. I think that it is a kind of conditional cross-release or something even more special. Sigh, I wish I was able to clean my head even more to be able to think about this. Best Regards, Petr
