When busy-spinning on a ww_mutex_trylock(), we depend upon the other
thread advancing and releasing the lock. This can not happen on a single
CPU unless we relinquish it:
[ ] NMI watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [kworker/0:1:18]
...
[ ] Call Trace:
[ ] mutex_trylock()
[ ] test_mutex_work+0x31/0x56
[ ] process_one_work+0x1b4/0x2f9
[ ] worker_thread+0x1b0/0x27c
[ ] kthread+0xd1/0xd3
[ ] ret_from_fork+0x19/0x30
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes:
f2a5fec17395 ("locking/ww_mutex: Begin kselftests for ww_mutex")
Link: http://lkml.kernel.org/r/20170228094011.2595-1-chris@chris-wilson.co.uk
Signed-off-by: Ingo Molnar <mingo@kernel.org>
if (mtx->flags & TEST_MTX_TRY) {
while (!ww_mutex_trylock(&mtx->mutex))
- cpu_relax();
+ cond_resched();
} else {
ww_mutex_lock(&mtx->mutex, NULL);
}
ret = -EINVAL;
break;
}
- cpu_relax();
+ cond_resched();
} while (time_before(jiffies, timeout));
} else {
ret = wait_for_completion_timeout(&mtx.done, TIMEOUT);