[tip:WIP.timers/core 27/68] include/linux/rcupdate.h:644:9: sparse: sparse: context imbalance in 'timer_wait_running' - unexpected unlock
From: kbuild test robot
Date: Mon Aug 19 2019 - 17:13:30 EST
tree: https://kernel.googlesource.com/pub/scm/linux/kernel/git/tip/tip.git WIP.timers/core
head: b16101077c4444bc7e0dde91e7ffb258ce1f979b
commit: e51f39feec02940feeb0914ef9ff8fe5e05965c1 [27/68] posix-timer: Use a callback for cancel synchronization
reproduce:
# apt-get install sparse
# sparse version: v0.6.1-rc1-7-g2b96cd8-dirty
git checkout e51f39feec02940feeb0914ef9ff8fe5e05965c1
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@xxxxxxxxx>
sparse warnings: (new ones prefixed by >>)
kernel/time/posix-timers.c:588:24: sparse: sparse: context imbalance in '__lock_timer' - different lock contexts for basic block
>> include/linux/rcupdate.h:644:9: sparse: sparse: context imbalance in 'timer_wait_running' - unexpected unlock
kernel/time/posix-timers.c:870:12: sparse: sparse: context imbalance in 'do_timer_settime' - different lock contexts for basic block
kernel/time/posix-timers.c:976:1: sparse: sparse: context imbalance in '__se_sys_timer_delete' - different lock contexts for basic block
vim +/timer_wait_running +644 include/linux/rcupdate.h
^1da177e4c3f41 Linus Torvalds 2005-04-16 596
^1da177e4c3f41 Linus Torvalds 2005-04-16 597 /*
^1da177e4c3f41 Linus Torvalds 2005-04-16 598 * So where is rcu_write_lock()? It does not exist, as there is no
^1da177e4c3f41 Linus Torvalds 2005-04-16 599 * way for writers to lock out RCU readers. This is a feature, not
^1da177e4c3f41 Linus Torvalds 2005-04-16 600 * a bug -- this property is what provides RCU's performance benefits.
^1da177e4c3f41 Linus Torvalds 2005-04-16 601 * Of course, writers must coordinate with each other. The normal
^1da177e4c3f41 Linus Torvalds 2005-04-16 602 * spinlock primitives work well for this, but any other technique may be
^1da177e4c3f41 Linus Torvalds 2005-04-16 603 * used as well. RCU does not care how the writers keep out of each
^1da177e4c3f41 Linus Torvalds 2005-04-16 604 * others' way, as long as they do so.
^1da177e4c3f41 Linus Torvalds 2005-04-16 605 */
3d76c082907e8f Paul E. McKenney 2009-09-28 606
3d76c082907e8f Paul E. McKenney 2009-09-28 607 /**
ca5ecddfa8fcbd Paul E. McKenney 2010-04-28 608 * rcu_read_unlock() - marks the end of an RCU read-side critical section.
3d76c082907e8f Paul E. McKenney 2009-09-28 609 *
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 610 * In most situations, rcu_read_unlock() is immune from deadlock.
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 611 * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock()
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 612 * is responsible for deboosting, which it does via rt_mutex_unlock().
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 613 * Unfortunately, this function acquires the scheduler's runqueue and
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 614 * priority-inheritance spinlocks. This means that deadlock could result
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 615 * if the caller of rcu_read_unlock() already holds one of these locks or
ec84b27f9b3b56 Anna-Maria Gleixner 2018-05-25 616 * any lock that is ever acquired while holding them.
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 617 *
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 618 * That said, RCU readers are never priority boosted unless they were
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 619 * preempted. Therefore, one way to avoid deadlock is to make sure
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 620 * that preemption never happens within any RCU read-side critical
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 621 * section whose outermost rcu_read_unlock() is called with one of
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 622 * rt_mutex_unlock()'s locks held. Such preemption can be avoided in
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 623 * a number of ways, for example, by invoking preempt_disable() before
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 624 * critical section's outermost rcu_read_lock().
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 625 *
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 626 * Given that the set of locks acquired by rt_mutex_unlock() might change
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 627 * at any time, a somewhat more future-proofed approach is to make sure
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 628 * that that preemption never happens within any RCU read-side critical
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 629 * section whose outermost rcu_read_unlock() is called with irqs disabled.
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 630 * This approach relies on the fact that rt_mutex_unlock() currently only
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 631 * acquires irq-disabled locks.
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 632 *
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 633 * The second of these two approaches is best in most situations,
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 634 * however, the first approach can also be useful, at least to those
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 635 * developers willing to keep abreast of the set of locks acquired by
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 636 * rt_mutex_unlock().
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 637 *
3d76c082907e8f Paul E. McKenney 2009-09-28 638 * See rcu_read_lock() for more information.
3d76c082907e8f Paul E. McKenney 2009-09-28 639 */
bc33f24bdca8b6 Paul E. McKenney 2009-08-22 640 static inline void rcu_read_unlock(void)
bc33f24bdca8b6 Paul E. McKenney 2009-08-22 641 {
f78f5b90c4ffa5 Paul E. McKenney 2015-06-18 642 RCU_LOCKDEP_WARN(!rcu_is_watching(),
bde23c6892878e Heiko Carstens 2012-02-01 643 "rcu_read_unlock() used illegally while idle");
bc33f24bdca8b6 Paul E. McKenney 2009-08-22 @644 __release(RCU);
bc33f24bdca8b6 Paul E. McKenney 2009-08-22 645 __rcu_read_unlock();
d24209bb689e2c Paul E. McKenney 2015-01-21 646 rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
bc33f24bdca8b6 Paul E. McKenney 2009-08-22 647 }
^1da177e4c3f41 Linus Torvalds 2005-04-16 648
:::::: The code at line 644 was first introduced by commit
:::::: bc33f24bdca8b6e97376e3a182ab69e6cdefa989 rcu: Consolidate sparse and lockdep declarations in include/linux/rcupdate.h
:::::: TO: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
:::::: CC: Ingo Molnar <mingo@xxxxxxx>
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