Date: Mon, 30 Jul 2012 11:49:43 -0400 From: John Baldwin <jhb@freebsd.org> To: Konstantin Belousov <kostikbel@gmail.com> Cc: Attilio Rao <attilio@freebsd.org>, Davide Italiano <davide@freebsd.org>, src-committers@freebsd.org, svn-src-projects@freebsd.org Subject: Re: svn commit: r238907 - projects/calloutng/sys/kern Message-ID: <201207301149.43458.jhb@freebsd.org> In-Reply-To: <20120730143943.GY2676@deviant.kiev.zoral.com.ua> References: <201207301350.q6UDobCI099069@svn.freebsd.org> <CAJ-FndBmXkyJJ=fCkEpVm84E56A2_EoM6kbch03e4RMEM6WCGQ@mail.gmail.com> <20120730143943.GY2676@deviant.kiev.zoral.com.ua>
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On Monday, July 30, 2012 10:39:43 am Konstantin Belousov wrote: > On Mon, Jul 30, 2012 at 03:24:26PM +0100, Attilio Rao wrote: > > On 7/30/12, Davide Italiano <davide@freebsd.org> wrote: > > > On Mon, Jul 30, 2012 at 4:02 PM, Attilio Rao <attilio@freebsd.org> wrote: > > > Thanks for the comment, Attilio. > > > Yes, it's exactly what you thought. If direct flag is equal to one > > > you're sure you're processing a callout which runs directly from > > > hardware interrupt context. In this case, the running thread cannot > > > sleep and it's likely you have TDP_NOSLEEPING flags set, failing the > > > KASSERT() in THREAD_NO_SLEEPING() and leading to panic if kernel is > > > compiled with INVARIANTS. > > > In case you're running from SWI context (direct equals to zero) code > > > remains the same as before. > > > I think what I'm doing works due the assumption thread running never > > > sleeps. Do you suggest some other way to handle this? > > > > Possibly the quicker way to do this is to have a way to deal with the > > TDP_NOSLEEPING flag in recursed way, thus implement the same logic as > > VFS_LOCK_GIANT() does, for example. > > You will need to change the few callers of THREAD_NO_SLEEPING(), but > > the patch should be no longer than 10/15 lines. > > There are already curthread_pflags_set/restore KPI designed exactly to handle > nested private thread flags. > > Also, I wonder, should you assert somehow that direct dispatch cannot block > as well ? Hmm, I have a nested TDP_NOSLEEPING already (need it to fix an issue in rmlocks). It uses a count though as the flag is set during rm_rlock() and released during rm_runlock(). I don't think it could use a set/restore KPI as there is no good place to store the state. -- John Baldwin
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