Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754126AbXJINYu (ORCPT ); Tue, 9 Oct 2007 09:24:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752280AbXJINYm (ORCPT ); Tue, 9 Oct 2007 09:24:42 -0400 Received: from smtp114.sbc.mail.mud.yahoo.com ([68.142.198.213]:46490 "HELO smtp114.sbc.mail.mud.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752659AbXJINYl (ORCPT ); Tue, 9 Oct 2007 09:24:41 -0400 X-YMail-OSG: EXHkFmUVM1lqvmWP7PK3UtgN4YdNd.rQKjGDgQtFq7yzLJtg7tRjJUW8s1H8FaghQnLWRAg666bETeHiEKzS3OBNaiPWghIEiI0.OnAEGpXY01uEITI- Date: Tue, 9 Oct 2007 08:24:37 -0500 From: "Serge E. Hallyn" To: Pierre Peiffer Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH] IPC: cleanup some code and wrong comments about semundo list managment Message-ID: <20071009132437.GA18312@vino.hallyn.com> References: <20071005164606.284341c9.Pierre.Peiffer@bull.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20071005164606.284341c9.Pierre.Peiffer@bull.net> User-Agent: Mutt/1.5.16 (2007-06-09) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4692 Lines: 137 Quoting Pierre Peiffer (Pierre.Peiffer@bull.net): > 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). I see, that was changed since commit 00a5dfdb93f74e4d95fb0d83c890728e331f8810 in 2005 :) > Finally, (un)lock_semundo functions are useless, so remove them > for simplification. (this avoids an useless if statement) Looks correct. > Signed-off-by: Pierre Peiffer Acked-by: Serge Hallyn > --- > > 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/ - 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/