[cip:linux-4.19.y-cip-rt-rebase 96/9999] kernel/softirq.c:973 __tasklet_schedule_common() warn: inconsistent returns 'flags'.

[kernel test robot <lkp@intel.com>]

BCC: lkp@intel.com
CC: oe-kbuild-all@lists.linux.dev
TO: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/cip/linux-cip.git linux-4.19.y-cip-rt-rebase
head:   67ac3270c7aaf93810ea5b43e2bf8361b683718e
commit: 62d0a2a30cd01fabc7f6555df2cfae7dd3d9fad8 [96/9999] tasklet: Address a race resulting in double-enqueue
:::::: branch date: 4 days ago
:::::: commit date: 4 years, 5 months ago
config: i386-randconfig-141-20240927 (https://download.01.org/0day-ci/archive/20240928/202409280623.vGQgQ1pn-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Reported-by: Dan Carpenter <error27@gmail.com>
| Closes: https://lore.kernel.org/r/202409280623.vGQgQ1pn-lkp@intel.com/

smatch warnings:
kernel/softirq.c:973 __tasklet_schedule_common() warn: inconsistent returns 'flags'.

vim +/flags +973 kernel/softirq.c

^1da177e4c3f41 Linus Torvalds 2005-04-16  928  
6498ddad301c7a Ingo Molnar    2018-02-27  929  static void __tasklet_schedule_common(struct tasklet_struct *t,
6498ddad301c7a Ingo Molnar    2018-02-27  930  				      struct tasklet_head __percpu *headp,
6498ddad301c7a Ingo Molnar    2018-02-27  931  				      unsigned int softirq_nr)
^1da177e4c3f41 Linus Torvalds 2005-04-16  932  {
6498ddad301c7a Ingo Molnar    2018-02-27  933  	struct tasklet_head *head;
^1da177e4c3f41 Linus Torvalds 2005-04-16  934  	unsigned long flags;
^1da177e4c3f41 Linus Torvalds 2005-04-16  935  
^1da177e4c3f41 Linus Torvalds 2005-04-16  936  	local_irq_save(flags);
4a8c8d729198e3 Ingo Molnar    2011-11-29  937  	if (!tasklet_trylock(t)) {
4a8c8d729198e3 Ingo Molnar    2011-11-29  938  		local_irq_restore(flags);
4a8c8d729198e3 Ingo Molnar    2011-11-29  939  		return;
4a8c8d729198e3 Ingo Molnar    2011-11-29  940  	}
4a8c8d729198e3 Ingo Molnar    2011-11-29  941  
6498ddad301c7a Ingo Molnar    2018-02-27  942  	head = this_cpu_ptr(headp);
4a8c8d729198e3 Ingo Molnar    2011-11-29  943  again:
4a8c8d729198e3 Ingo Molnar    2011-11-29  944  	/* We may have been preempted before tasklet_trylock
4a8c8d729198e3 Ingo Molnar    2011-11-29  945  	 * and __tasklet_action may have already run.
4a8c8d729198e3 Ingo Molnar    2011-11-29  946  	 * So double check the sched bit while the takslet
4a8c8d729198e3 Ingo Molnar    2011-11-29  947  	 * is locked before adding it to the list.
4a8c8d729198e3 Ingo Molnar    2011-11-29  948  	 */
4a8c8d729198e3 Ingo Molnar    2011-11-29  949  	if (test_bit(TASKLET_STATE_SCHED, &t->state)) {
62d0a2a30cd01f Zhang Xiao     2020-03-17  950  		if (test_and_set_bit(TASKLET_STATE_CHAINED, &t->state)) {
62d0a2a30cd01f Zhang Xiao     2020-03-17  951  			tasklet_unlock(t);
62d0a2a30cd01f Zhang Xiao     2020-03-17  952  			return;
62d0a2a30cd01f Zhang Xiao     2020-03-17  953  		}
48f20a9a9488c4 Olof Johansson 2008-03-04  954  		t->next = NULL;
6498ddad301c7a Ingo Molnar    2018-02-27  955  		*head->tail = t;
6498ddad301c7a Ingo Molnar    2018-02-27  956  		head->tail = &(t->next);
6498ddad301c7a Ingo Molnar    2018-02-27  957  		raise_softirq_irqoff(softirq_nr);
4a8c8d729198e3 Ingo Molnar    2011-11-29  958  		tasklet_unlock(t);
4a8c8d729198e3 Ingo Molnar    2011-11-29  959  	} else {
4a8c8d729198e3 Ingo Molnar    2011-11-29  960  		/* This is subtle. If we hit the corner case above
4a8c8d729198e3 Ingo Molnar    2011-11-29  961  		 * It is possible that we get preempted right here,
4a8c8d729198e3 Ingo Molnar    2011-11-29  962  		 * and another task has successfully called
4a8c8d729198e3 Ingo Molnar    2011-11-29  963  		 * tasklet_schedule(), then this function, and
4a8c8d729198e3 Ingo Molnar    2011-11-29  964  		 * failed on the trylock. Thus we must be sure
4a8c8d729198e3 Ingo Molnar    2011-11-29  965  		 * before releasing the tasklet lock, that the
4a8c8d729198e3 Ingo Molnar    2011-11-29  966  		 * SCHED_BIT is clear. Otherwise the tasklet
4a8c8d729198e3 Ingo Molnar    2011-11-29  967  		 * may get its SCHED_BIT set, but not added to the
4a8c8d729198e3 Ingo Molnar    2011-11-29  968  		 * list
4a8c8d729198e3 Ingo Molnar    2011-11-29  969  		 */
4a8c8d729198e3 Ingo Molnar    2011-11-29  970  		if (!tasklet_tryunlock(t))
4a8c8d729198e3 Ingo Molnar    2011-11-29  971  			goto again;
4a8c8d729198e3 Ingo Molnar    2011-11-29  972  	}
^1da177e4c3f41 Linus Torvalds 2005-04-16 @973  	local_irq_restore(flags);
^1da177e4c3f41 Linus Torvalds 2005-04-16  974  }
6498ddad301c7a Ingo Molnar    2018-02-27  975  

:::::: The code at line 973 was first introduced by commit
:::::: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 Linux-2.6.12-rc2

:::::: TO: Linus Torvalds <torvalds@ppc970.osdl.org>
:::::: CC: Linus Torvalds <torvalds@ppc970.osdl.org>

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki