linux-kernel - Re: [PATCH] rcu: mollify sparse with RCU guard

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Date: Tue, 26 Mar 2024 10:39:24 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Johannes Berg <johannes@...solutions.net>
Cc: Boqun Feng <boqun.feng@...il.com>, rcu@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	Josh Triplett <josh@...htriplett.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] rcu: mollify sparse with RCU guard

On Mon, Mar 25, 2024 at 07:43:18PM +0100, Johannes Berg wrote:
> On Mon, 2024-03-25 at 21:28 +0300, Dan Carpenter wrote:
> > On Mon, Mar 25, 2024 at 05:41:22PM +0100, Johannes Berg wrote:
> > > Also __acquire()/__release() are just empty macros without __CHECKER__.
> > > So not sure the indirection really is warranted for this special case.
> > > 
> > > I can add a comment in there, I guess, something like
> > > 
> > >  /* sparse doesn't actually "call" cleanup functions */
> > > 
> > > perhaps. That reminds me I forgot to CC Dan ...
> > > 
> > 
> > These are Sparse warnings, not Smatch warning... Smatch doesn't use any
> > of the Sparse locking annotations.
> 
> Sure, of course. I just saw that you added cleanup stuff to sparse to
> allow using it in smatch.
> 
> > Smatch handles cleanup basically correctly at this point.
> 
> Do you "run" / "emit" the cleanup function calls there?

Yes.

> I briefly look
> at doing that in sparse but it felt ... complicated, and then I saw the
> condition in the cleanup function which I thought sparse could probably
> not see through anyway.

The if (_T->lock) statements are a problem.  For those, I have to
manually add them to check_locking.c as an unlock function and to
check_preempt.c as a decrement the preempt count function.  The other
place that I have to add them is to smatch_data/db/kernel.return_fixes
because the scoped_guard() macros checks them as well.  I had to do
quite a bit of patching things up when the sound subsystem started using
cleanup.h so here is an example of what that looks like:

https://github.com/error27/smatch/commit/a2f68c96f70a0cdc581beff81eb6d412ac8dfc4f

regards,
dan carpenter