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); rcu_read_unlock(); break; }
