Re: [PATCH v3 5/9] seqlock, kcsan: Add annotations for KCSAN

From: kbuild test robot
Date: Tue Nov 05 2019 - 06:35:53 EST

Hi Marco,

I love your patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[also build test WARNING on v5.4-rc6]
[cannot apply to next-20191031]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url: https://github.com/0day-ci/linux/commits/Marco-Elver/Add-Kernel-Concurrency-Sanitizer-KCSAN/20191105-002542
base: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git a99d8080aaf358d5d23581244e5da23b35e340b9
reproduce:
# apt-get install sparse
# sparse version: v0.6.1-6-g57f8611-dirty
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 >>)

>> include/linux/rcupdate.h:651:9: sparse: sparse: context imbalance in 'thread_group_cputime' - different lock contexts for basic block

vim +/thread_group_cputime +651 include/linux/rcupdate.h

^1da177e4c3f41 Linus Torvalds 2005-04-16 603
^1da177e4c3f41 Linus Torvalds 2005-04-16 604 /*
^1da177e4c3f41 Linus Torvalds 2005-04-16 605 * So where is rcu_write_lock()? It does not exist, as there is no
^1da177e4c3f41 Linus Torvalds 2005-04-16 606 * way for writers to lock out RCU readers. This is a feature, not
^1da177e4c3f41 Linus Torvalds 2005-04-16 607 * a bug -- this property is what provides RCU's performance benefits.
^1da177e4c3f41 Linus Torvalds 2005-04-16 608 * Of course, writers must coordinate with each other. The normal
^1da177e4c3f41 Linus Torvalds 2005-04-16 609 * spinlock primitives work well for this, but any other technique may be
^1da177e4c3f41 Linus Torvalds 2005-04-16 610 * used as well. RCU does not care how the writers keep out of each
^1da177e4c3f41 Linus Torvalds 2005-04-16 611 * others' way, as long as they do so.
^1da177e4c3f41 Linus Torvalds 2005-04-16 612 */
3d76c082907e8f Paul E. McKenney 2009-09-28 613
3d76c082907e8f Paul E. McKenney 2009-09-28 614 /**
ca5ecddfa8fcbd Paul E. McKenney 2010-04-28 615 * rcu_read_unlock() - marks the end of an RCU read-side critical section.
3d76c082907e8f Paul E. McKenney 2009-09-28 616 *
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 617 * In most situations, rcu_read_unlock() is immune from deadlock.
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 618 * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock()
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 619 * is responsible for deboosting, which it does via rt_mutex_unlock().
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 620 * Unfortunately, this function acquires the scheduler's runqueue and
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 621 * priority-inheritance spinlocks. This means that deadlock could result
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 622 * if the caller of rcu_read_unlock() already holds one of these locks or
ec84b27f9b3b56 Anna-Maria Gleixner 2018-05-25 623 * any lock that is ever acquired while holding them.
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 624 *
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 625 * That said, RCU readers are never priority boosted unless they were
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 626 * preempted. Therefore, one way to avoid deadlock is to make sure
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 627 * that preemption never happens within any RCU read-side critical
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 628 * section whose outermost rcu_read_unlock() is called with one of
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 629 * rt_mutex_unlock()'s locks held. Such preemption can be avoided in
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 630 * a number of ways, for example, by invoking preempt_disable() before
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 631 * critical section's outermost rcu_read_lock().
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 632 *
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 633 * Given that the set of locks acquired by rt_mutex_unlock() might change
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 634 * at any time, a somewhat more future-proofed approach is to make sure
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 635 * that that preemption never happens within any RCU read-side critical
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 636 * section whose outermost rcu_read_unlock() is called with irqs disabled.
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 637 * This approach relies on the fact that rt_mutex_unlock() currently only
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 638 * acquires irq-disabled locks.
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 639 *
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 640 * The second of these two approaches is best in most situations,
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 641 * however, the first approach can also be useful, at least to those
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 642 * developers willing to keep abreast of the set of locks acquired by
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 643 * rt_mutex_unlock().
f27bc4873fa8b7 Paul E. McKenney 2014-05-04 644 *
3d76c082907e8f Paul E. McKenney 2009-09-28 645 * See rcu_read_lock() for more information.
3d76c082907e8f Paul E. McKenney 2009-09-28 646 */
bc33f24bdca8b6 Paul E. McKenney 2009-08-22 647 static inline void rcu_read_unlock(void)
bc33f24bdca8b6 Paul E. McKenney 2009-08-22 648 {
f78f5b90c4ffa5 Paul E. McKenney 2015-06-18 649 RCU_LOCKDEP_WARN(!rcu_is_watching(),
bde23c6892878e Heiko Carstens 2012-02-01 650 "rcu_read_unlock() used illegally while idle");
bc33f24bdca8b6 Paul E. McKenney 2009-08-22 @651 __release(RCU);
bc33f24bdca8b6 Paul E. McKenney 2009-08-22 652 __rcu_read_unlock();
d24209bb689e2c Paul E. McKenney 2015-01-21 653 rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
bc33f24bdca8b6 Paul E. McKenney 2009-08-22 654 }
^1da177e4c3f41 Linus Torvalds 2005-04-16 655

:::::: The code at line 651 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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