Commit c530c6ac authored by Pierre Peiffer's avatar Pierre Peiffer Committed by Linus Torvalds
Browse files

IPC: cleanup some code and wrong comments about semundo list managment 



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: default avatarPierre Peiffer <pierre.peiffer@bull.net>
Cc: Nadia Derbey <Nadia.Derbey@bull.net>
Acked-by: default avatarSerge Hallyn <serue@us.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1b531f21

ipc/sem.c

+6 −40
Original line number Diff line number Diff line
@@ -999,36 +999,6 @@ 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
@@ -1089,9 +1059,9 @@ 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;
@@ -1114,10 +1084,10 @@ 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);
@@ -1128,7 +1098,7 @@ 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;
@@ -1139,7 +1109,7 @@ 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;

}
@@ -1315,10 +1285,6 @@ 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)

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