From: Peter Zijlstra <peterz@infradead.org>
To: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
linux-rt-users <linux-rt-users@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: Re: [btrfs/rt] lockdep false positive
Date: Mon, 23 Jan 2017 10:07:51 +0100 [thread overview]
Message-ID: <20170123090751.GU6485@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1485107114.4467.73.camel@gmail.com>
On Sun, Jan 22, 2017 at 06:45:14PM +0100, Mike Galbraith wrote:
> On Sun, 2017-01-22 at 09:46 +0100, Mike Galbraith wrote:
> > Greetings btrfs/lockdep wizards,
> >
> > RT trees have trouble with the BTRFS lockdep positive avoidance lock
> > class dance (see disk-io.c). Seems the trouble is due to RT not having
> > a means of telling lockdep that its rwlocks are recursive for read by
> > the lock owner only, combined with the BTRFS lock class dance assuming
> > that read_lock() is annotated rwlock_acquire_read(), which RT cannot
> > do, as that would be a big fat lie.
> >
> > Creating a rt_read_lock_shared() for btrfs_clear_lock_blocking_rw() did
> > indeed make lockdep happy as a clam for test purposes. (hm, submitting
> > that would be excellent way to replenish frozen shark supply:)
> >
> > Ideas?
Not having looked at anything much, currently lockdep does not in fact
model rwlock properly as is.
Note that rwlock is _not_ in fact reader biased like it used to be, that
is, read_lock() will block if there is a pending writer (just like
rwsem), with the exception when read_lock() happend in_interrupt()
(because tasklist_lock).
next prev parent reply other threads:[~2017-01-23 9:08 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-22 8:46 [btrfs/rt] lockdep false positive Mike Galbraith
2017-01-22 17:45 ` Mike Galbraith
2017-01-22 18:25 ` Mike Galbraith
2017-01-23 5:23 ` Mike Galbraith
2017-01-23 9:07 ` Peter Zijlstra [this message]
2017-01-25 17:02 ` Sebastian Andrzej Siewior
2017-01-25 18:29 ` Mike Galbraith
2017-01-26 17:09 ` Sebastian Andrzej Siewior
2017-01-26 18:01 ` Mike Galbraith
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