locking/qrwlock: Use atomic_cond_read_acquire() when spinning in qrwlock

The qrwlock slowpaths involve spinning when either a prospective reader
is waiting for a concurrent writer to drain, or a prospective writer is
waiting for concurrent readers to drain. In both of these situations,
atomic_cond_read_acquire() can be used to avoid busy-waiting and make use
of any backoff functionality provided by the architecture.

This patch replaces the open-code loops and rspin_until_writer_unlock()
implementation with atomic_cond_read_acquire(). The write mode transition
zero to _QW_WAITING is left alone, since (a) this doesn't need acquire
semantics and (b) should be fast.

Tested-by: Waiman Long <[email protected]>
Tested-by: Jeremy Linton <[email protected]>
Tested-by: Adam Wallis <[email protected]>
Tested-by: Jan Glauber <[email protected]>
Signed-off-by: Will Deacon <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: [email protected]
Cc: Linus Torvalds <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

0 files changed, 0 insertions, 0 deletions