From: Pierre Peiffer <pierre.peiffer@bull.net>
Some comments about sem_undo_list seem wrong.
About the comment above unlock_semundo:
"... If task2 now exits before task1 releases the lock (by calling
unlock_semundo()), then task1 will never call spin_unlock(). ..."
This is just wrong, I see no reason for which task1 will not call
spin_unlock... The rest of this comment is also wrong... Unless I
miss something (of course).
Finally, (un)lock_semundo functions are useless, so remove them
for simplification. (this avoids an useless if statement)
Signed-off-by: Pierre Peiffer <pierre.peiffer@bull.net>
---
ipc/sem.c | 46 ++++++----------------------------------------
1 files changed, 6 insertions(+), 40 deletions(-)
diff --git a/ipc/sem.c b/ipc/sem.c
index b676fef..5585817 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -957,36 +957,6 @@ asmlinkage long sys_semctl (int semid, int semnum, int cmd, union semun arg)
}
}
-static inline void lock_semundo(void)
-{
- struct sem_undo_list *undo_list;
-
- undo_list = current->sysvsem.undo_list;
- if (undo_list)
- spin_lock(&undo_list->lock);
-}
-
-/* This code has an interaction with copy_semundo().
- * Consider; two tasks are sharing the undo_list. task1
- * acquires the undo_list lock in lock_semundo(). If task2 now
- * exits before task1 releases the lock (by calling
- * unlock_semundo()), then task1 will never call spin_unlock().
- * This leave the sem_undo_list in a locked state. If task1 now creats task3
- * and once again shares the sem_undo_list, the sem_undo_list will still be
- * locked, and future SEM_UNDO operations will deadlock. This case is
- * dealt with in copy_semundo() by having it reinitialize the spin lock when
- * the refcnt goes from 1 to 2.
- */
-static inline void unlock_semundo(void)
-{
- struct sem_undo_list *undo_list;
-
- undo_list = current->sysvsem.undo_list;
- if (undo_list)
- spin_unlock(&undo_list->lock);
-}
-
-
/* If the task doesn't already have a undo_list, then allocate one
* here. We guarantee there is only one thread using this undo list,
* and current is THE ONE
@@ -1047,9 +1017,9 @@ static struct sem_undo *find_undo(struct ipc_namespace *ns, int semid)
if (error)
return ERR_PTR(error);
- lock_semundo();
+ spin_lock(&ulp->lock);
un = lookup_undo(ulp, semid);
- unlock_semundo();
+ spin_unlock(&ulp->lock);
if (likely(un!=NULL))
goto out;
@@ -1077,10 +1047,10 @@ static struct sem_undo *find_undo(struct ipc_namespace *ns, int semid)
new->semadj = (short *) &new[1];
new->semid = semid;
- lock_semundo();
+ spin_lock(&ulp->lock);
un = lookup_undo(ulp, semid);
if (un) {
- unlock_semundo();
+ spin_unlock(&ulp->lock);
kfree(new);
ipc_lock_by_ptr(&sma->sem_perm);
ipc_rcu_putref(sma);
@@ -1091,7 +1061,7 @@ static struct sem_undo *find_undo(struct ipc_namespace *ns, int semid)
ipc_rcu_putref(sma);
if (sma->sem_perm.deleted) {
sem_unlock(sma);
- unlock_semundo();
+ spin_unlock(&ulp->lock);
kfree(new);
un = ERR_PTR(-EIDRM);
goto out;
@@ -1102,7 +1072,7 @@ static struct sem_undo *find_undo(struct ipc_namespace *ns, int semid)
sma->undo = new;
sem_unlock(sma);
un = new;
- unlock_semundo();
+ spin_unlock(&ulp->lock);
out:
return un;
}
@@ -1279,10 +1249,6 @@ asmlinkage long sys_semop (int semid, struct sembuf __user *tsops, unsigned nsop
/* If CLONE_SYSVSEM is set, establish sharing of SEM_UNDO state between
* parent and child tasks.
- *
- * See the notes above unlock_semundo() regarding the spin_lock_init()
- * in this code. Initialize the undo_list->lock here instead of get_undo_list()
- * because of the reasoning in the comment above unlock_semundo.
*/
int copy_semundo(unsigned long clone_flags, struct task_struct *tsk)
Pierre Peiffer
-
