[PATCH -mm] ipc,sem: fix locking in semctl_main

[Rik van Riel <riel@redhat.com>]

Andrew, here is the patch I promised :)

Everywhere else in the code, we check sma->sem_perm.deleted under
the semaphore array lock, so we should do teh same here.
The easy fix is to simply not drop and re-take the lock, but keep
it locked.

This patch can be folded into ipcsem-fine-grained-locking-for-semtimedop.patch

Signed-off-by: Rik van Riel <riel@redhat.com>
---
 ipc/sem.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/ipc/sem.c b/ipc/sem.c
index 5711616..efdaee6 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -1243,10 +1243,9 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
 				err = -EIDRM;
 				goto out_free;
 			}
-			sem_unlock(sma, -1);
-		}
+		} else
+			sem_lock(sma, NULL, -1);
 
-		sem_lock(sma, NULL, -1);
 		for (i = 0; i < sma->sem_nsems; i++)
 			sem_io[i] = sma->sem_base[i].semval;
 		sem_unlock(sma, -1);