4.18-stable review patch. If anyone has any objections, please let me know.
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[ Upstream commit e4a02ed2aaf447fa849e3254bfdb3b9b01e1e520 ]
If CONFIG_WW_MUTEX_SELFTEST=y is enabled, booting an image in an arm64 virtual machine results in the following traceback if 8 CPUs are enabled:
DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current) WARNING: CPU: 2 PID: 537 at kernel/locking/mutex.c:1033 __mutex_unlock_slowpath+0x1a8/0x2e0 ... Call trace: __mutex_unlock_slowpath() ww_mutex_unlock() test_cycle_work() process_one_work() worker_thread() kthread() ret_from_fork()
If requesting b_mutex fails with -EDEADLK, the error variable is reassigned to the return value from calling ww_mutex_lock on a_mutex again. If this call fails, a_mutex is not locked. It is, however, unconditionally unlocked subsequently, causing the reported warning. Fix the problem by using two error variables.
With this change, the selftest still fails as follows:
cyclic deadlock not resolved, ret[7/8] = -35
However, the traceback is gone.
Signed-off-by: Guenter Roeck linux@roeck-us.net Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Will Deacon will.deacon@arm.com Fixes: d1b42b800e5d0 ("locking/ww_mutex: Add kselftests for resolving ww_mutex cyclic deadlocks") Link: http://lkml.kernel.org/r/1538516929-9734-1-git-send-email-linux@roeck-us.net Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/locking/test-ww_mutex.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c index 0e4cd64ad2c0..654977862b06 100644 --- a/kernel/locking/test-ww_mutex.c +++ b/kernel/locking/test-ww_mutex.c @@ -260,7 +260,7 @@ static void test_cycle_work(struct work_struct *work) { struct test_cycle *cycle = container_of(work, typeof(*cycle), work); struct ww_acquire_ctx ctx; - int err; + int err, erra = 0;
ww_acquire_init(&ctx, &ww_class); ww_mutex_lock(&cycle->a_mutex, &ctx); @@ -270,17 +270,19 @@ static void test_cycle_work(struct work_struct *work)
err = ww_mutex_lock(cycle->b_mutex, &ctx); if (err == -EDEADLK) { + err = 0; ww_mutex_unlock(&cycle->a_mutex); ww_mutex_lock_slow(cycle->b_mutex, &ctx); - err = ww_mutex_lock(&cycle->a_mutex, &ctx); + erra = ww_mutex_lock(&cycle->a_mutex, &ctx); }
if (!err) ww_mutex_unlock(cycle->b_mutex); - ww_mutex_unlock(&cycle->a_mutex); + if (!erra) + ww_mutex_unlock(&cycle->a_mutex); ww_acquire_fini(&ctx);
- cycle->result = err; + cycle->result = err ?: erra; }
static int __test_cycle(unsigned int nthreads)