The owner field in the rw_semaphore structure is used primarily for optimistic spinning. However, identifying the rwsem owner can also be helpful in debugging as well as tracing locking related issues when analyzing crash dump. The owner field may also store state information that can be important to the operation of the rwsem. So the owner field is now made a permanent member of the rw_semaphore structure irrespective of CONFIG_RWSEM_SPIN_ON_OWNER.
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| @@ -34,12 +34,12 @@ · 33 unmodified lines | ||
| 34 | 34 | */ |
| 35 | 35 | struct rw_semaphore { |
| 36 | 36 | atomic_long_t count; |
| 37 | −#ifdef CONFIG_RWSEM_SPIN_ON_OWNER | |
| 38 | 37 | /* |
| 39 | − * Write owner. Used as a speculative check to see | |
| 40 | − * if the owner is running on the cpu. | |
| 38 | + * Write owner or one of the read owners. Can be used as a | |
| 39 | + * speculative check to see if the owner is running on the cpu. | |
| 41 | 40 | */ |
| 42 | 41 | struct task_struct *owner; |
| 42 | +#ifdef CONFIG_RWSEM_SPIN_ON_OWNER | |
| 43 | 43 | struct optimistic_spin_queue osq; /* spinner MCS lock */ |
| 44 | 44 | #endif |
| 45 | 45 | raw_spinlock_t wait_lock; |
| @@ -73,13 +73,14 @@ static inline int rwsem_is_locked(struct rw_semaphore *sem) · 27 unmodified lines | ||
| 73 | 73 | #endif |
| 74 | 74 | |
| 75 | 75 | #ifdef CONFIG_RWSEM_SPIN_ON_OWNER |
| 76 | −#define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL | |
| 76 | +#define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED | |
| 77 | 77 | #else |
| 78 | 78 | #define __RWSEM_OPT_INIT(lockname) |
| 79 | 79 | #endif |
| 80 | 80 | |
| 81 | 81 | #define __RWSEM_INITIALIZER(name) \ |
| 82 | 82 | { __RWSEM_INIT_COUNT(name), \ |
| 83 | + .owner = NULL, \ | |
| 83 | 84 | .wait_list = LIST_HEAD_INIT((name).wait_list), \ |
| 84 | 85 | .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \ |
| 85 | 86 | __RWSEM_OPT_INIT(name) \ |