Re: [PATCH RFC 06/26] ipc: Replace spin_unlock_wait() with lock/unlock pair

[Manfred Spraul]

On 06/30/2017 02:01 AM, Paul E. McKenney wrote:

There is no agreed-upon definition of spin_unlock_wait()'s semantics,
and it appears that all callers could do just as well with a lock/unlock
pair.  This commit therefore replaces the spin_unlock_wait() call in
exit_sem() with spin_lock() followed immediately by spin_unlock().
This should be safe from a performance perspective because exit_sem()
is rarely invoked in production.

Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Davidlohr Bueso <d...@stgolabs.net>
Cc: Manfred Spraul <manf...@colorfullife.com>
Cc: Will Deacon <will.dea...@arm.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Alan Stern <st...@rowland.harvard.edu>
Cc: Andrea Parri <parri.and...@gmail.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>

Acked-by: Manfred Spraul <manf...@colorfullife.com>

---
  ipc/sem.c | 3 ++-
  1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/ipc/sem.c b/ipc/sem.c
index 947dc2348271..e88d0749a929 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -2096,7 +2096,8 @@ void exit_sem(struct task_struct *tsk)
                         * possibility where we exit while freeary() didn't
                         * finish unlocking sem_undo_list.
                         */
-                       spin_unlock_wait(&ulp->lock);
+                       spin_lock(&ulp->lock);
+                       spin_unlock(&ulp->lock);
                        rcu_read_unlock();
                        break;
                }