[kbuild-all] [oracle-dtrace:v2/5.17-rc2 8/10] fs/eventpoll.c:1224:3: warning: Assignment of function parameter has no effect outside the function. Did you forget dereferencing it? [uselessAssignmentPtrArg]

Thursday, 10 February 2022


tree:   https://github.com/oracle/dtrace-linux-kernel v2/5.17-rc2
head:   47946e7b2e2319f39cbb7f8aaa294298c2dec5b4
commit: 16ad67b61ac4f3dd93b3fa6875a011fff7b88500 [8/10] waitfd: new syscall implementing
waitpid() over fds
compiler: or1k-linux-gcc (GCC) 11.2.0

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp(a)intel.com&gt;


cppcheck possible warnings: (new ones prefixed by >>, may not be real problems)

...
> fs/eventpoll.c:1224:3: warning: Assignment of function parameter
has no effect outside the function. Did you forget dereferencing it?
[uselessAssignmentPtrArg]       key = (void *)epi->fixed_event;
      ^

vim +1224 fs/eventpoll.c

a218cc4914209a Roman Penyaev      2019-03-07  1118
^1da177e4c3f41 Linus Torvalds     2005-04-16  1119  /*
7699acd1341c63 Davide Libenzi     2007-05-10  1120   * This is the callback that is passed
to the wait queue wakeup
bf6a41db7726e6 Daniel Baluta      2011-01-30  1121   * mechanism. It is called by the
stored file descriptors when they
7699acd1341c63 Davide Libenzi     2007-05-10  1122   * have events to report.
a218cc4914209a Roman Penyaev      2019-03-07  1123   *
a6c67fee9cf095 Randy Dunlap       2021-03-01  1124   * This callback takes a read lock in
order not to contend with concurrent
a6c67fee9cf095 Randy Dunlap       2021-03-01  1125   * events from another file
descriptor, thus all modifications to ->rdllist
a218cc4914209a Roman Penyaev      2019-03-07  1126   * or ->ovflist are lockless.  Read
lock is paired with the write lock from
a218cc4914209a Roman Penyaev      2019-03-07  1127   * ep_scan_ready_list(), which stops
all list modifications and guarantees
a218cc4914209a Roman Penyaev      2019-03-07  1128   * that lists state is seen
correctly.
a218cc4914209a Roman Penyaev      2019-03-07  1129   *
a218cc4914209a Roman Penyaev      2019-03-07  1130   * Another thing worth to mention is
that ep_poll_callback() can be called
a218cc4914209a Roman Penyaev      2019-03-07  1131   * concurrently for the same @epi from
different CPUs if poll table was inited
a218cc4914209a Roman Penyaev      2019-03-07  1132   * with several wait queues entries. 
Plural wakeup from different CPUs of a
a218cc4914209a Roman Penyaev      2019-03-07  1133   * single wait queue is serialized by
wq.lock, but the case when multiple wait
a218cc4914209a Roman Penyaev      2019-03-07  1134   * queues are used should be detected
accordingly.  This is detected using
a218cc4914209a Roman Penyaev      2019-03-07  1135   * cmpxchg() operation.
^1da177e4c3f41 Linus Torvalds     2005-04-16  1136   */
ac6424b981bce1 Ingo Molnar        2017-06-20  1137  static int
ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, void *key)
^1da177e4c3f41 Linus Torvalds     2005-04-16  1138  {
7699acd1341c63 Davide Libenzi     2007-05-10  1139  	int pwake = 0;
7699acd1341c63 Davide Libenzi     2007-05-10  1140  	struct epitem *epi =
ep_item_from_wait(wait);
7699acd1341c63 Davide Libenzi     2007-05-10  1141  	struct eventpoll *ep = epi->ep;
3ad6f93e98d6df Al Viro            2017-07-03  1142  	__poll_t pollflags =
key_to_poll(key);
a218cc4914209a Roman Penyaev      2019-03-07  1143  	unsigned long flags;
df0108c5da561c Jason Baron        2016-01-20  1144  	int ewake = 0;
^1da177e4c3f41 Linus Torvalds     2005-04-16  1145
a218cc4914209a Roman Penyaev      2019-03-07  1146  	read_lock_irqsave(&ep->lock,
flags);
^1da177e4c3f41 Linus Torvalds     2005-04-16  1147
bf3b9f6372c45b Sridhar Samudrala  2017-03-24  1148  	ep_set_busy_poll_napi_id(epi);
bf3b9f6372c45b Sridhar Samudrala  2017-03-24  1149
^1da177e4c3f41 Linus Torvalds     2005-04-16  1150  	/*
7699acd1341c63 Davide Libenzi     2007-05-10  1151  	 * If the event mask does not contain
any poll(2) event, we consider the
7699acd1341c63 Davide Libenzi     2007-05-10  1152  	 * descriptor to be disabled. This
condition is likely the effect of the
7699acd1341c63 Davide Libenzi     2007-05-10  1153  	 * EPOLLONESHOT bit that disables the
descriptor when an event is received,
7699acd1341c63 Davide Libenzi     2007-05-10  1154  	 * until the next EPOLL_CTL_MOD will
be issued.
^1da177e4c3f41 Linus Torvalds     2005-04-16  1155  	 */
7699acd1341c63 Davide Libenzi     2007-05-10  1156  	if (!(epi->event.events &
~EP_PRIVATE_BITS))
d47de16c722196 Davide Libenzi     2007-05-15  1157  		goto out_unlock;
d47de16c722196 Davide Libenzi     2007-05-15  1158
2dfa4eeab0fc7e Davide Libenzi     2009-03-31  1159  	/*
2dfa4eeab0fc7e Davide Libenzi     2009-03-31  1160  	 * Check the events coming with the
callback. At this stage, not
2dfa4eeab0fc7e Davide Libenzi     2009-03-31  1161  	 * every device reports the events in
the "key" parameter of the
2dfa4eeab0fc7e Davide Libenzi     2009-03-31  1162  	 * callback. We need to be able to
handle both cases here, hence the
2dfa4eeab0fc7e Davide Libenzi     2009-03-31  1163  	 * test for "key" != NULL
before the event match test.
2dfa4eeab0fc7e Davide Libenzi     2009-03-31  1164  	 */
3ad6f93e98d6df Al Viro            2017-07-03  1165  	if (pollflags && !(pollflags
& epi->event.events))
2dfa4eeab0fc7e Davide Libenzi     2009-03-31  1166  		goto out_unlock;
2dfa4eeab0fc7e Davide Libenzi     2009-03-31  1167
d47de16c722196 Davide Libenzi     2007-05-15  1168  	/*
bf6a41db7726e6 Daniel Baluta      2011-01-30  1169  	 * If we are transferring events to
userspace, we can hold no locks
d47de16c722196 Davide Libenzi     2007-05-15  1170  	 * (because we're accessing user
memory, and because of linux f_op->poll()
bf6a41db7726e6 Daniel Baluta      2011-01-30  1171  	 * semantics). All the events that
happen during that period of time are
d47de16c722196 Davide Libenzi     2007-05-15  1172  	 * chained in ep->ovflist and
requeued later on.
d47de16c722196 Davide Libenzi     2007-05-15  1173  	 */
c5a282e9635e9c Davidlohr Bueso    2019-01-03  1174  	if (READ_ONCE(ep->ovflist) !=
EP_UNACTIVE_PTR) {
0c54a6a44bf3d4 Khazhismel Kumykov 2020-05-07  1175  		if (chain_epi_lockless(epi))
c3e320b61581ef Roman Penyaev      2019-03-07  1176  			ep_pm_stay_awake_rcu(epi);
0c54a6a44bf3d4 Khazhismel Kumykov 2020-05-07  1177  	} else if (!ep_is_linked(epi)) {
0c54a6a44bf3d4 Khazhismel Kumykov 2020-05-07  1178  		/* In the usual case, add event to
ready list. */
0c54a6a44bf3d4 Khazhismel Kumykov 2020-05-07  1179  		if
(list_add_tail_lockless(&epi->rdllink, &ep->rdllist))
eea1d585917c53 Eric Wong          2013-04-30  1180  			ep_pm_stay_awake_rcu(epi);
4d7e30d98939a0 Arve Hjønnevåg     2012-05-01  1181  	}
7699acd1341c63 Davide Libenzi     2007-05-10  1182
7699acd1341c63 Davide Libenzi     2007-05-10  1183  	/*
7699acd1341c63 Davide Libenzi     2007-05-10  1184  	 * Wake up ( if active ) both the
eventpoll wait list and the ->poll()
7699acd1341c63 Davide Libenzi     2007-05-10  1185  	 * wait list.
7699acd1341c63 Davide Libenzi     2007-05-10  1186  	 */
df0108c5da561c Jason Baron        2016-01-20  1187  	if (waitqueue_active(&ep->wq))
{
b6a515c8a0f6c2 Jason Baron        2016-02-05  1188  		if ((epi->event.events &
EPOLLEXCLUSIVE) &&
3ad6f93e98d6df Al Viro            2017-07-03  1189  					!(pollflags & POLLFREE)) {
3ad6f93e98d6df Al Viro            2017-07-03  1190  			switch (pollflags &
EPOLLINOUT_BITS) {
a9a08845e9acbd Linus Torvalds     2018-02-11  1191  			case EPOLLIN:
a9a08845e9acbd Linus Torvalds     2018-02-11  1192  				if (epi->event.events &
EPOLLIN)
b6a515c8a0f6c2 Jason Baron        2016-02-05  1193  					ewake = 1;
b6a515c8a0f6c2 Jason Baron        2016-02-05  1194  				break;
a9a08845e9acbd Linus Torvalds     2018-02-11  1195  			case EPOLLOUT:
a9a08845e9acbd Linus Torvalds     2018-02-11  1196  				if (epi->event.events &
EPOLLOUT)
b6a515c8a0f6c2 Jason Baron        2016-02-05  1197  					ewake = 1;
b6a515c8a0f6c2 Jason Baron        2016-02-05  1198  				break;
b6a515c8a0f6c2 Jason Baron        2016-02-05  1199  			case 0:
df0108c5da561c Jason Baron        2016-01-20  1200  				ewake = 1;
b6a515c8a0f6c2 Jason Baron        2016-02-05  1201  				break;
b6a515c8a0f6c2 Jason Baron        2016-02-05  1202  			}
b6a515c8a0f6c2 Jason Baron        2016-02-05  1203  		}
a218cc4914209a Roman Penyaev      2019-03-07  1204  		wake_up(&ep->wq);
df0108c5da561c Jason Baron        2016-01-20  1205  	}
7699acd1341c63 Davide Libenzi     2007-05-10  1206  	if
(waitqueue_active(&ep->poll_wait))
7699acd1341c63 Davide Libenzi     2007-05-10  1207  		pwake++;
^1da177e4c3f41 Linus Torvalds     2005-04-16  1208
d47de16c722196 Davide Libenzi     2007-05-15  1209  out_unlock:
a218cc4914209a Roman Penyaev      2019-03-07  1210 
	read_unlock_irqrestore(&ep->lock, flags);
7699acd1341c63 Davide Libenzi     2007-05-10  1211
7699acd1341c63 Davide Libenzi     2007-05-10  1212  	/* We have to call this outside the
lock */
7699acd1341c63 Davide Libenzi     2007-05-10  1213  	if (pwake)
efcdd350d1f8a9 Jason Baron        2020-04-06  1214  		ep_poll_safewake(ep, epi);
7699acd1341c63 Davide Libenzi     2007-05-10  1215
138e4ad67afd5c Oleg Nesterov      2017-09-01  1216  	if (!(epi->event.events &
EPOLLEXCLUSIVE))
138e4ad67afd5c Oleg Nesterov      2017-09-01  1217  		ewake = 1;
138e4ad67afd5c Oleg Nesterov      2017-09-01  1218
16ad67b61ac4f3 Nick Alcock        2018-11-14  1219  	/*
16ad67b61ac4f3 Nick Alcock        2018-11-14  1220  	 * If this fd type has a hardwired
event which should override the key
16ad67b61ac4f3 Nick Alcock        2018-11-14  1221  	 * (e.g. if it is waiting on a
non-file waitqueue), jam it in here.
16ad67b61ac4f3 Nick Alcock        2018-11-14  1222  	 */
16ad67b61ac4f3 Nick Alcock        2018-11-14  1223  	if (epi->fixed_event)
16ad67b61ac4f3 Nick Alcock        2018-11-14 @1224  		key = (void *)epi->fixed_event;
16ad67b61ac4f3 Nick Alcock        2018-11-14  1225
3ad6f93e98d6df Al Viro            2017-07-03  1226  	if (pollflags & POLLFREE) {
138e4ad67afd5c Oleg Nesterov      2017-09-01  1227  		/*
138e4ad67afd5c Oleg Nesterov      2017-09-01  1228  		 * If we race with
ep_remove_wait_queue() it can miss
138e4ad67afd5c Oleg Nesterov      2017-09-01  1229  		 * ->whead = NULL and do another
remove_wait_queue() after
138e4ad67afd5c Oleg Nesterov      2017-09-01  1230  		 * us, so we can't use
__remove_wait_queue().
138e4ad67afd5c Oleg Nesterov      2017-09-01  1231  		 */
138e4ad67afd5c Oleg Nesterov      2017-09-01  1232  		list_del_init(&wait->entry);
138e4ad67afd5c Oleg Nesterov      2017-09-01  1233  		/*
138e4ad67afd5c Oleg Nesterov      2017-09-01  1234  		 * ->whead != NULL protects us
from the race with ep_free()
138e4ad67afd5c Oleg Nesterov      2017-09-01  1235  		 * or ep_remove(),
ep_remove_wait_queue() takes whead->lock
138e4ad67afd5c Oleg Nesterov      2017-09-01  1236  		 * held by the caller. Once we
nullify it, nothing protects
138e4ad67afd5c Oleg Nesterov      2017-09-01  1237  		 * ep/epi or even wait.
138e4ad67afd5c Oleg Nesterov      2017-09-01  1238  		 */
138e4ad67afd5c Oleg Nesterov      2017-09-01  1239 
		smp_store_release(&ep_pwq_from_wait(wait)->whead, NULL);
138e4ad67afd5c Oleg Nesterov      2017-09-01  1240  	}
df0108c5da561c Jason Baron        2016-01-20  1241
138e4ad67afd5c Oleg Nesterov      2017-09-01  1242  	return ewake;
7699acd1341c63 Davide Libenzi     2007-05-10  1243  }
^1da177e4c3f41 Linus Torvalds     2005-04-16  1244

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[kbuild-all] [oracle-dtrace:v2/5.17-rc2 8/10] fs/eventpoll.c:1224:3: warning: Assignment of function parameter has no effect outside the function. Did you forget dereferencing it? [uselessAssignmentPtrArg]