On Wed, Jun 08, 2016 at 06:35:08AM -0700, Mark Johnston wrote: > On Wed, Jun 08, 2016 at 07:30:55AM +0300, Konstantin Belousov wrote: > > On Tue, Jun 07, 2016 at 11:19:19PM +0200, Jilles Tjoelker wrote: > > > I also wonder whether we may be overengineering things here. Perhaps > > > the advlock sleep can simply turn off TDF_SBDRY. > > Well, this was the very first patch suggested. I would be fine with that, > > but again, out-of-tree code seems to be not quite fine with that local > > solution. > > In our particular case, we could possibly use a similar approach. In > general, it seems incorrect to clear TDF_SBDRY if the thread calling > sx_sleep() has any locks held. It is easy to verify that all callers of > lf_advlock() are safe in this respect, but this kind of auditing is > generally hard. In fact, I believe the sx_sleep that led to the problem > described in D2612 is the same as the one in my case. That is, the > sleeping thread may or may not hold a vnode lock depending on context.
I do not think that in-tree code sleeps with a vnode lock held in the lf_advlock(). Otherwise, system would hang in lock cascade by an attempt to obtain an advisory lock. I think we can even assert this with witness. There is another sleep, which Jilles mentioned, in lf_purgelocks(), called from vgone(). This sleep indeed occurs under the vnode lock, and as such must be non-suspendable. The sleep waits until other threads leave the lf_advlock() for the reclaimed vnode, and they should leave in deterministic time due to issued wakeups. So this sleep is exempt from the considerations, and TDF_SBDRY there is correct. I am fine with either the braces around sx_sleep() in lf_advlock() to clear TDF_SBDRY (sigdeferstsop()), or with the latest patch I sent, which adds temporal override for TDF_SBDRY with TDF_SRESTART. My understanding is that you prefer the later. If I do not mis-represent your position, I understand why you do prefer that. _______________________________________________ firstname.lastname@example.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to "freebsd-current-unsubscr...@freebsd.org"