rwsem: more agressive lock stealing in rwsem_down_write_failed
Some small code simplifications can be achieved by doing more agressive
lock stealing:
- When rwsem_down_write_failed() notices that there are no active locks
(and thus no thread to wake us if we decided to sleep), it used to wake
the first queued process. However, stealing the lock is also sufficient
to deal with this case, so we don't need this check anymore.
- In try_get_writer_sem(), we can steal the lock even when the first waiter
is a reader. This is correct because the code path that wakes readers is
protected by the wait_lock. As to the performance effects of this change,
they are expected to be minimal: readers are still granted the lock
(rather than having to acquire it themselves) when they reach the front
of the wait queue, so we have essentially the same behavior as in
rwsem-spinlock.
Signed-off-by: Michel Lespinasse <walken@google.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Acked-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 file changed