Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763259AbXJEOqe (ORCPT ); Fri, 5 Oct 2007 10:46:34 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755344AbXJEOqP (ORCPT ); Fri, 5 Oct 2007 10:46:15 -0400 Received: from ecfrec.frec.bull.fr ([129.183.4.8]:33231 "EHLO ecfrec.frec.bull.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757015AbXJEOqN (ORCPT ); Fri, 5 Oct 2007 10:46:13 -0400 Date: Fri, 5 Oct 2007 16:46:06 +0200 From: Pierre Peiffer To: linux-kernel@vger.kernel.org Subject: [PATCH] IPC: cleanup some code and wrong comments about semundo list managment Message-Id: <20071005164606.284341c9.Pierre.Peiffer@bull.net> X-Mailer: Sylpheed 2.3.1 (GTK+ 2.10.14; i386-redhat-linux-gnu) Mime-Version: 1.0 X-MIMETrack: Itemize by SMTP Server on ECN002/FR/BULL(Release 5.0.12 |February 13, 2003) at 05/10/2007 16:52:25, Serialize by Router on ECN002/FR/BULL(Release 5.0.12 |February 13, 2003) at 05/10/2007 16:52:26, Serialize complete at 05/10/2007 16:52:26 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4006 Lines: 124 From: Pierre Peiffer 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 --- 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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/