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Subject[PATCH 11/11] Task watchers: Register per-task semundo watcher
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This patch switches semundo from using the global task_watchers notifier chain
to a per-task notifier chain. In the case where a task does not use SysV
semaphores this would save a call to exit_sem().

Based off Jes Sorensen's patch implementing this with task_notifiers.

Signed-off-by: Matt Helsley <matthltc@us.ibm.com>
Cc: Jes Sorensen <jes@sgi.com>
--

ipc/sem.c | 23 ++++++++++++++++-------
1 files changed, 16 insertions(+), 7 deletions(-)

Index: linux-2.6.17-rc6-mm2/ipc/sem.c
===================================================================
--- linux-2.6.17-rc6-mm2.orig/ipc/sem.c
+++ linux-2.6.17-rc6-mm2/ipc/sem.c
@@ -139,14 +139,10 @@ static int sem_undo_task_exit(struct not
default: /* Don't care */
return NOTIFY_DONE;
}
}

-static struct notifier_block sem_watch_tasks_nb = {
- .notifier_call = sem_undo_task_exit
-};
-
static void __ipc_init __sem_init_ns(struct ipc_namespace *ns, struct ipc_ids *ids)
{
ns->ids[IPC_SEM_IDS] = ids;
ns->sc_semmsl = SEMMSL;
ns->sc_semmns = SEMMNS;
@@ -193,11 +189,10 @@ void __init sem_init (void)
{
__sem_init_ns(&init_ipc_ns, &init_sem_ids);
ipc_init_proc_interface("sysvipc/sem",
" key semid perms nsems uid gid cuid cgid otime ctime\n",
IPC_SEM_IDS, sysvipc_sem_proc_show);
- register_task_watcher(&sem_watch_tasks_nb);
}

/*
* Lockless wakeup algorithm:
* Without the check/retry algorithm a lockless wakeup is possible:
@@ -1010,11 +1005,10 @@ static inline void unlock_semundo(void)
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
*
* If this allocation and assignment succeeds, but later
@@ -1026,24 +1020,39 @@ static inline void unlock_semundo(void)
*/
static inline int get_undo_list(struct sem_undo_list **undo_listp)
{
struct sem_undo_list *undo_list;
int size;
+ struct notifier_block *semun_nb;
+ int retval;

undo_list = current->sysvsem.undo_list;
if (!undo_list) {
+ semun_nb = NULL;
+ retval = -ENOMEM;
size = sizeof(struct sem_undo_list);
undo_list = (struct sem_undo_list *) kmalloc(size, GFP_KERNEL);
if (undo_list == NULL)
- return -ENOMEM;
+ goto err;
+ semun_nb = kzalloc(sizeof(*semun_nb), GFP_KERNEL);
+ if (semun_nb == NULL)
+ goto err;
+ semun_nb->notifier_call = sem_undo_task_exit;
+ retval = register_per_task_watcher(semun_nb);
+ if (retval)
+ goto err;
memset(undo_list, 0, size);
spin_lock_init(&undo_list->lock);
atomic_set(&undo_list->refcnt, 1);
current->sysvsem.undo_list = undo_list;
}
*undo_listp = undo_list;
return 0;
+err:
+ kfree(semun_nb);
+ kfree(undo_list);
+ return retval;
}

static struct sem_undo *lookup_undo(struct sem_undo_list *ulp, int semid)
{
struct sem_undo **last, *un;
--

-
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