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Date: Thu, 25 Apr 2019 07:56:25 +0800
From: kbuild test robot <lkp@...el.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: kbuild-all@...org, netdev@...r.kernel.org
Subject: [net-next:master 292/294] include/linux/rcupdate.h:647:9: sparse:
context imbalance in 'tipc_udp_recv' - unexpected unlock
tree: https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git master
head: c049d56eb219661c9ae48d596c3e633973f89d1f
commit: 4109a2c3b91e5f38e401fc4ea56848e65e429785 [292/294] tipc: tipc_udp_recv() cleanup vs rcu verbs
reproduce:
# apt-get install sparse
git checkout 4109a2c3b91e5f38e401fc4ea56848e65e429785
make ARCH=x86_64 allmodconfig
make C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__'
If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@...el.com>
sparse warnings: (new ones prefixed by >>)
vim +/tipc_udp_recv +647 include/linux/rcupdate.h
^1da177e4 Linus Torvalds 2005-04-16 599
^1da177e4 Linus Torvalds 2005-04-16 600 /*
^1da177e4 Linus Torvalds 2005-04-16 601 * So where is rcu_write_lock()? It does not exist, as there is no
^1da177e4 Linus Torvalds 2005-04-16 602 * way for writers to lock out RCU readers. This is a feature, not
^1da177e4 Linus Torvalds 2005-04-16 603 * a bug -- this property is what provides RCU's performance benefits.
^1da177e4 Linus Torvalds 2005-04-16 604 * Of course, writers must coordinate with each other. The normal
^1da177e4 Linus Torvalds 2005-04-16 605 * spinlock primitives work well for this, but any other technique may be
^1da177e4 Linus Torvalds 2005-04-16 606 * used as well. RCU does not care how the writers keep out of each
^1da177e4 Linus Torvalds 2005-04-16 607 * others' way, as long as they do so.
^1da177e4 Linus Torvalds 2005-04-16 608 */
3d76c0829 Paul E. McKenney 2009-09-28 609
3d76c0829 Paul E. McKenney 2009-09-28 610 /**
ca5ecddfa Paul E. McKenney 2010-04-28 611 * rcu_read_unlock() - marks the end of an RCU read-side critical section.
3d76c0829 Paul E. McKenney 2009-09-28 612 *
f27bc4873 Paul E. McKenney 2014-05-04 613 * In most situations, rcu_read_unlock() is immune from deadlock.
f27bc4873 Paul E. McKenney 2014-05-04 614 * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock()
f27bc4873 Paul E. McKenney 2014-05-04 615 * is responsible for deboosting, which it does via rt_mutex_unlock().
f27bc4873 Paul E. McKenney 2014-05-04 616 * Unfortunately, this function acquires the scheduler's runqueue and
f27bc4873 Paul E. McKenney 2014-05-04 617 * priority-inheritance spinlocks. This means that deadlock could result
f27bc4873 Paul E. McKenney 2014-05-04 618 * if the caller of rcu_read_unlock() already holds one of these locks or
ec84b27f9 Anna-Maria Gleixner 2018-05-25 619 * any lock that is ever acquired while holding them.
f27bc4873 Paul E. McKenney 2014-05-04 620 *
f27bc4873 Paul E. McKenney 2014-05-04 621 * That said, RCU readers are never priority boosted unless they were
f27bc4873 Paul E. McKenney 2014-05-04 622 * preempted. Therefore, one way to avoid deadlock is to make sure
f27bc4873 Paul E. McKenney 2014-05-04 623 * that preemption never happens within any RCU read-side critical
f27bc4873 Paul E. McKenney 2014-05-04 624 * section whose outermost rcu_read_unlock() is called with one of
f27bc4873 Paul E. McKenney 2014-05-04 625 * rt_mutex_unlock()'s locks held. Such preemption can be avoided in
f27bc4873 Paul E. McKenney 2014-05-04 626 * a number of ways, for example, by invoking preempt_disable() before
f27bc4873 Paul E. McKenney 2014-05-04 627 * critical section's outermost rcu_read_lock().
f27bc4873 Paul E. McKenney 2014-05-04 628 *
f27bc4873 Paul E. McKenney 2014-05-04 629 * Given that the set of locks acquired by rt_mutex_unlock() might change
f27bc4873 Paul E. McKenney 2014-05-04 630 * at any time, a somewhat more future-proofed approach is to make sure
f27bc4873 Paul E. McKenney 2014-05-04 631 * that that preemption never happens within any RCU read-side critical
f27bc4873 Paul E. McKenney 2014-05-04 632 * section whose outermost rcu_read_unlock() is called with irqs disabled.
f27bc4873 Paul E. McKenney 2014-05-04 633 * This approach relies on the fact that rt_mutex_unlock() currently only
f27bc4873 Paul E. McKenney 2014-05-04 634 * acquires irq-disabled locks.
f27bc4873 Paul E. McKenney 2014-05-04 635 *
f27bc4873 Paul E. McKenney 2014-05-04 636 * The second of these two approaches is best in most situations,
f27bc4873 Paul E. McKenney 2014-05-04 637 * however, the first approach can also be useful, at least to those
f27bc4873 Paul E. McKenney 2014-05-04 638 * developers willing to keep abreast of the set of locks acquired by
f27bc4873 Paul E. McKenney 2014-05-04 639 * rt_mutex_unlock().
f27bc4873 Paul E. McKenney 2014-05-04 640 *
3d76c0829 Paul E. McKenney 2009-09-28 641 * See rcu_read_lock() for more information.
3d76c0829 Paul E. McKenney 2009-09-28 642 */
bc33f24bd Paul E. McKenney 2009-08-22 643 static inline void rcu_read_unlock(void)
bc33f24bd Paul E. McKenney 2009-08-22 644 {
f78f5b90c Paul E. McKenney 2015-06-18 645 RCU_LOCKDEP_WARN(!rcu_is_watching(),
bde23c689 Heiko Carstens 2012-02-01 646 "rcu_read_unlock() used illegally while idle");
bc33f24bd Paul E. McKenney 2009-08-22 @647 __release(RCU);
bc33f24bd Paul E. McKenney 2009-08-22 648 __rcu_read_unlock();
d24209bb6 Paul E. McKenney 2015-01-21 649 rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
bc33f24bd Paul E. McKenney 2009-08-22 650 }
^1da177e4 Linus Torvalds 2005-04-16 651
:::::: The code at line 647 was first introduced by commit
:::::: bc33f24bdca8b6e97376e3a182ab69e6cdefa989 rcu: Consolidate sparse and lockdep declarations in include/linux/rcupdate.h
:::::: TO: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
:::::: CC: Ingo Molnar <mingo@...e.hu>
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