From: Alexander Sverdlin alexander.sverdlin@siemens.com
KCSAN reports:
BUG: KCSAN: data-race in do_raw_write_lock / do_raw_write_lock
write (marked) to 0xffff800009cf504c of 4 bytes by task 1102 on cpu 1: do_raw_write_lock+0x120/0x204 _raw_write_lock_irq do_exit call_usermodehelper_exec_async ret_from_fork
read to 0xffff800009cf504c of 4 bytes by task 1103 on cpu 0: do_raw_write_lock+0x88/0x204 _raw_write_lock_irq do_exit call_usermodehelper_exec_async ret_from_fork
value changed: 0xffffffff -> 0x00000001
Reported by Kernel Concurrency Sanitizer on: CPU: 0 PID: 1103 Comm: kworker/u4:1 6.1.111
Commit 1a365e822372 ("locking/spinlock/debug: Fix various data races") has adressed most of these races, but seems to be not consistent/not complete.
From do_raw_write_lock() only debug_write_lock_after() part has been converted to WRITE_ONCE(), but not debug_write_lock_before() part. Do it now.
Cc: stable@vger.kernel.org Fixes: 1a365e822372 ("locking/spinlock/debug: Fix various data races") Reported-by: Adrian Freihofer adrian.freihofer@siemens.com Acked-by: Waiman Long longman@redhat.com Signed-off-by: Alexander Sverdlin alexander.sverdlin@siemens.com --- There are still some inconsistencies remaining IMO: - lock->magic is sometimes accessed with READ_ONCE() even though it's only being plain-written; - debug_spin_unlock() and debug_write_unlock() both do WRITE_ONCE() on lock->owner and lock->owner_cpu, but examine them with plain read accesses.
kernel/locking/spinlock_debug.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/locking/spinlock_debug.c b/kernel/locking/spinlock_debug.c index 87b03d2e41dbb..2338b3adfb55f 100644 --- a/kernel/locking/spinlock_debug.c +++ b/kernel/locking/spinlock_debug.c @@ -184,8 +184,8 @@ void do_raw_read_unlock(rwlock_t *lock) static inline void debug_write_lock_before(rwlock_t *lock) { RWLOCK_BUG_ON(lock->magic != RWLOCK_MAGIC, lock, "bad magic"); - RWLOCK_BUG_ON(lock->owner == current, lock, "recursion"); - RWLOCK_BUG_ON(lock->owner_cpu == raw_smp_processor_id(), + RWLOCK_BUG_ON(READ_ONCE(lock->owner) == current, lock, "recursion"); + RWLOCK_BUG_ON(READ_ONCE(lock->owner_cpu) == raw_smp_processor_id(), lock, "cpu recursion"); }