From: Boqun Feng <boqun.feng@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
Andrea Parri <parri.andrea@gmail.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Josh Triplett <josh@joshtriplett.org>,
Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Subject: Re: [RFC tip/locking/lockdep v6 19/20] rcu: Equip sleepable RCU with lockdep dependency graph checks
Date: Fri, 13 Apr 2018 21:24:44 +0800 [thread overview]
Message-ID: <20180413132444.wb2liczapxxizrne@tardis> (raw)
In-Reply-To: <20180412091217.GY4082@hirez.programming.kicks-ass.net>
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On Thu, Apr 12, 2018 at 11:12:17AM +0200, Peter Zijlstra wrote:
> On Thu, Apr 12, 2018 at 10:12:33AM +0800, Boqun Feng wrote:
> > A trivial fix/hack would be adding local_irq_disable() and
> > local_irq_enable() around srcu_lock_sync() like:
> >
> > static inline void srcu_lock_sync(struct lockdep_map *map)
> > {
> > local_irq_disable();
> > lock_map_acquire(map);
> > lock_map_release(map);
> > local_irq_enable();
> > }
> >
> > However, it might be better, if lockdep could provide some annotation
> > API for such an empty critical section to say the grap-and-drop is
> > atomic. Something like:
> >
> > /*
> > * Annotate a wait point for all previous critical section to
> > * go out.
> > *
> > * This won't make @map a irq unsafe lock, no matter it's called
> > * w/ or w/o irq disabled.
> > */
> > lock_wait_unlock(struct lockdep_map *map, ..)
> >
> > And in this primitive, we do something similar like
> > lock_acquire()+lock_release(). This primitive could be used elsewhere,
> > as I bebieve we have several empty grab-and-drop critical section for
> > lockdep annotations, e.g. in start_flush_work().
> >
> > Thoughts?
> >
> > This cerntainly requires a bit more work, in the meanwhile, I will add
> > another self testcase which has a srcu_read_lock() called in irq.
>
> Yeah, I've never really bothered to clean those things up, but I don't
> see any reason to stop you from doing it ;-)
>
> As to the initial pattern with disabling IRQs, I think I've seen code
> like that before, and in general performance isn't a top priority
Yeah, I saw we used that pattern in del_timer_sync()
> (within reason) when you're running lockdep kernels, so I've usually let
> it be.
Turns out it's not very hard to write a working version of
lock_wait_unlock() ;-) Just call __lock_acquire() and __lock_release()
back-to-back with the @hardirqoff for __lock_acquire() to be 1:
/*
* lock_sync() - synchronize with all previous critical sections to finish.
*
* Simply a acquire+release annotation with hardirqoff is true, because no lock
* is actually held, so this annotaion alone is safe to be interrupted as if
* irqs are off
*/
void lock_sync(struct lockdep_map *lock, unsigned subclass, int read,
int check, struct lockdep_map *nest_lock, unsigned long ip)
{
unsigned long flags;
if (unlikely(current->lockdep_recursion))
return;
raw_local_irq_save(flags);
check_flags(flags);
current->lockdep_recursion = 1;
__lock_acquire(lock, subclass, 0, read, check, 1, nest_lock, ip, 0, 0);
if (__lock_release(lock, 0, ip))
check_chain_key(current);
current->lockdep_recursion = 0;
raw_local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(lock_sync);
I rename as lock_sync(), because most of the time, we annotate with this
for a "sync point" with other critical sections. We can avoid some
overhead if we refactor __lock_acquire() and __lock_release() with some
helper functions, but I think this version is good enough for now, at
least better than disabling IRQs around lock_map_acquire() +
lock_map_release() ;-)
Thoughts?
Regards,
Boqun
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next prev parent reply other threads:[~2018-04-13 13:20 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-11 13:50 [RFC tip/locking/lockdep v6 00/20] lockdep: Support deadlock detection for recursive read locks Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 01/20] lockdep/Documention: Recursive read lock detection reasoning Boqun Feng
2018-04-15 0:38 ` Randy Dunlap
2018-04-16 6:29 ` Boqun Feng
2018-04-27 13:50 ` Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 02/20] lockdep: Demagic the return value of BFS Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 03/20] lockdep: Make __bfs() visit every dependency until a match Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 04/20] lockdep: Redefine LOCK_*_STATE* bits Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 05/20] lockdep: Reduce the size of lock_list::distance Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 06/20] lockdep: Introduce lock_list::dep Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 07/20] lockdep: Extend __bfs() to work with multiple types of dependencies Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 08/20] lockdep: Make __bfs(.match) return bool Boqun Feng
2018-04-11 13:50 ` [RFC tip/locking/lockdep v6 09/20] lockdep: Support deadlock detection for recursive read locks in check_noncircular() Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 10/20] lockdep: Adjust check_redundant() for recursive read change Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 11/20] lockdep: Fix recursive read lock related safe->unsafe detection Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 12/20] lockdep: Add recursive read locks into dependency graph Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 13/20] lockdep/selftest: Add a R-L/L-W test case specific to chain cache behavior Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 14/20] lockdep: Take read/write status in consideration when generate chainkey Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 15/20] lockdep/selftest: Unleash irq_read_recursion2 and add more Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 16/20] lockdep/selftest: Add more recursive read related test cases Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 17/20] Revert "locking/lockdep/selftests: Fix mixed read-write ABBA tests" Boqun Feng
2018-04-11 13:51 ` [RFC tip/locking/lockdep v6 18/20] MAINTAINERS: Add myself as a LOCKING PRIMITIVES reviewer Boqun Feng
2018-04-11 13:56 ` [RFC tip/locking/lockdep v6 19/20] rcu: Equip sleepable RCU with lockdep dependency graph checks Boqun Feng
2018-04-11 18:57 ` Paul E. McKenney
2018-04-12 2:12 ` Boqun Feng
2018-04-12 9:12 ` Peter Zijlstra
2018-04-13 13:24 ` Boqun Feng [this message]
2018-04-11 13:57 ` [RFC tip/locking/lockdep v6 20/20] lockdep/selftest: Add a test case for SRCU Boqun Feng
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