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s390/cmm: avoid add_timer on concurrently used timer 

cmm_set_timer could be called concurrently from cmm_thread, cmm proc
handler, upon cmm smsg receive and timer function itself. To avoid
potential race condition and hitting BUG_ON in add_timer on already
pending timer simply reuse mod_timer which is according to
documentation "the only safe way to modify the timeout" with multiple
unserialized concurrent users. mod_timer can handle both active and
inactive timers which allows to carry out minor code simplification as
well.

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Vasily Gorbik 2018-07-13 08:13:13 +02:00 committed by Martin Schwidefsky
parent a09baa9543
commit ac4c4fc87d
1 changed files with 1 additions and 6 deletions
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7
arch/s390/mm/cmm.c
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@ -191,12 +191,7 @@ static void cmm_set_timer(void)
del_timer(&cmm_timer);
return;
}
if (timer_pending(&cmm_timer)) {
if (mod_timer(&cmm_timer, jiffies + cmm_timeout_seconds*HZ))
return;
}
cmm_timer.expires = jiffies + cmm_timeout_seconds*HZ;
add_timer(&cmm_timer);
mod_timer(&cmm_timer, jiffies + cmm_timeout_seconds * HZ);
}
static void cmm_timer_fn(struct timer_list *unused)