On (09/07/18 08:39), Jiri Slaby wrote:
> > [ 244.944070]
> > [ 244.944070] Showing all locks held in the system:
> > [ 244.945558] 1 lock held by khungtaskd/18:
> > [ 244.946495] #0: (____ptrval____) (rcu_read_lock){....}, at: debug_show_all_locks+0x16/0x190
> > [ 244.948503] 2 locks held by askfirst/235:
> > [ 244.949439] #0: (____ptrval____) (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x25/0x50
> > [ 244.951762] #1: (____ptrval____) (&ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x13d/0xa00
>
> Here, it just seems to wait for input from the user.
>
> > [ 244.953799] 1 lock held by validate_data/655:
> > [ 244.954814] #0: (____ptrval____) (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x25/0x50
> > [ 244.956764] 1 lock held by dnsmasq/668:
> > [ 244.957649] #0: (____ptrval____) (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x25/0x50
> > [ 244.959598] 1 lock held by dropbear/734:
> > [ 244.967564] #0: (____ptrval____) (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x25/0x50
>
> Hmm, I assume there is another task waiting for write_ldsem and that one
> prevents these readers to proceed. Unfortunately, due to the defunct
> __ptrval__ pointer hashing crap, we do not see who is waiting for what.
> But I am guessing all are the same locks.
Hmm, interesting. Am I getting it right that the test did pass before.
And now we see that sort of/smells like live-lock right after the
introduction of tty_ldisc_lock() to tty_reopen().
> So I think, we are forced to limit the waiting to 5 seconds in reopen in
> the end too (the same as we do for new open in tty_init_dev).
If I got it right, LKP did test the 5*HZ patch
retval = tty_ldisc_lock(tty, 5 * HZ);
At least it's
In-Reply-To: <20180829022353.23568-3-dima@xxxxxxxxxx>
and
Message-Id: <20180829022353.23568-3-dima@xxxxxxxxxx>
is the patch which does the 5*HZ lock timeout thing.
-ss
