Date: Wed, 8 Jun 2016 06:35:08 -0700 From: Mark Johnston <markj@FreeBSD.org> To: Konstantin Belousov <kostikbel@gmail.com> Cc: Jilles Tjoelker <jilles@stack.nl>, freebsd-current@FreeBSD.org, cem@FreeBSD.org Subject: Re: thread suspension when dumping core Message-ID: <20160608133508.GA93263@charmander> In-Reply-To: <20160608043055.GV38613@kib.kiev.ua> References: <20160604022347.GA1096@wkstn-mjohnston.west.isilon.com> <20160604093236.GA38613@kib.kiev.ua> <20160606171311.GC10101@wkstn-mjohnston.west.isilon.com> <20160607024610.GI38613@kib.kiev.ua> <20160607041741.GA29017@wkstn-mjohnston.west.isilon.com> <20160607042956.GM38613@kib.kiev.ua> <20160607142452.GA48251@stack.nl> <20160607160155.GP38613@kib.kiev.ua> <20160607211919.GA49961@stack.nl> <20160608043055.GV38613@kib.kiev.ua>
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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: > > In this case it is clear which sleep(9) calls should be affected so it > > may be better to avoid more hidden state. > In this case yes, but apparently some out-of-tree users exist. And, > the marking of the single sx_sleep() call depends on knowing our > implementation. I remember that as the arguments to change from PBDRY to > the current state setter, in NFS it is not too hard to try to enumerate > interruptible sleeps. > > > > > 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.
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