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

From: Manfred Spraul
Date: Sat Jul 01 2017 - 15:23:40 EST

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 <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Cc: Andrea Parri <parri.andrea@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Acked-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
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);