Prepare to simplify lock acquistion by waiting writer. Derived from Michel Lespinasse's write lock stealing work on rwsem.
Cc: Michel Lespinasse <[email protected]> Signed-off-by: Peter Hurley <[email protected]> --- drivers/tty/tty_ldsem.c | 22 +++++++++++++++------- 1 file changed, 15 insertions(+), 7 deletions(-) diff --git a/drivers/tty/tty_ldsem.c b/drivers/tty/tty_ldsem.c index d2f091a..48f1ce8 100644 --- a/drivers/tty/tty_ldsem.c +++ b/drivers/tty/tty_ldsem.c @@ -136,13 +136,8 @@ static void __ldsem_wake_readers(struct ld_semaphore *sem) sem->wait_readers = 0; } -static void __ldsem_wake_writer(struct ld_semaphore *sem) +static inline int writer_trylock(struct ld_semaphore *sem) { - struct ldsem_waiter *waiter; - struct task_struct *tsk; - - waiter = list_entry(sem->write_wait.next, struct ldsem_waiter, list); - /* only wake this writer if the active part of the count can be * transitioned from 0 -> 1 */ @@ -159,9 +154,22 @@ static void __ldsem_wake_writer(struct ld_semaphore *sem) */ count = ldsem_atomic_update(-LDSEM_ACTIVE_BIAS, sem); if (count & LDSEM_ACTIVE_MASK) - return; + return 0; } while (1); + return 1; +} + +static void __ldsem_wake_writer(struct ld_semaphore *sem) +{ + struct ldsem_waiter *waiter; + struct task_struct *tsk; + + waiter = list_entry(sem->write_wait.next, struct ldsem_waiter, list); + + if (!writer_trylock(sem)) + return; + /* We must be careful not to touch 'waiter' after we set ->task = NULL. * It is an allocated on the waiter's stack and may become invalid at * any time after that point (due to a wakeup from another source). -- 1.8.1.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
