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Subject[PATCH v2 5/4] ipc: replace ipc_perm.lock with an rwlock
These patches go on top of Davidlohr's 4 patches. Performance numbers in patch "7"

---8<---

Replace the ipc_perm.lock with an rwlock, in preparation for
finer grained locking for semaphore operations.

Signed-off-by: Rik van Riel <riel@redhat.com>
---
include/linux/ipc.h | 2 +-
ipc/sem.c | 11 +++--------
ipc/shm.c | 2 +-
ipc/util.c | 12 ++++++------
ipc/util.h | 6 +++---
5 files changed, 14 insertions(+), 19 deletions(-)

diff --git a/include/linux/ipc.h b/include/linux/ipc.h
index 8d861b2..3c5e2aa 100644
--- a/include/linux/ipc.h
+++ b/include/linux/ipc.h
@@ -10,7 +10,7 @@
/* used by in-kernel data structures */
struct kern_ipc_perm
{
- spinlock_t lock;
+ rwlock_t lock;
int deleted;
int id;
key_t key;
diff --git a/ipc/sem.c b/ipc/sem.c
index f06a853..efb49e7 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -260,7 +260,7 @@ static inline void sem_putref(struct sem_array *sma)
*/
static inline void sem_getref(struct sem_array *sma)
{
- spin_lock(&(sma)->sem_perm.lock);
+ write_lock(&(sma)->sem_perm.lock);
ipc_rcu_getref(sma);
ipc_unlock(&(sma)->sem_perm);
}
@@ -778,7 +778,6 @@ static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
struct list_head tasks;

/* Free the existing undo structures for this semaphore set. */
- assert_spin_locked(&sma->sem_perm.lock);
list_for_each_entry_safe(un, tu, &sma->list_id, list_id) {
list_del(&un->list_id);
spin_lock(&un->ulp->lock);
@@ -977,7 +976,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
}
}

- spin_lock(&sma->sem_perm.lock);
+ write_lock(&sma->sem_perm.lock);
for (i = 0; i < sma->sem_nsems; i++)
sem_io[i] = sma->sem_base[i].semval;
sem_unlock(sma);
@@ -1025,7 +1024,6 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
for (i = 0; i < nsems; i++)
sma->sem_base[i].semval = sem_io[i];

- assert_spin_locked(&sma->sem_perm.lock);
list_for_each_entry(un, &sma->list_id, list_id) {
for (i = 0; i < nsems; i++)
un->semadj[i] = 0;
@@ -1042,7 +1040,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
if(semnum < 0 || semnum >= nsems)
goto out_unlock;

- spin_lock(&sma->sem_perm.lock);
+ write_lock(&sma->sem_perm.lock);
curr = &sma->sem_base[semnum];

switch (cmd) {
@@ -1067,7 +1065,6 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
if (val > SEMVMX || val < 0)
goto out_unlock;

- assert_spin_locked(&sma->sem_perm.lock);
list_for_each_entry(un, &sma->list_id, list_id)
un->semadj[semnum] = 0;

@@ -1345,7 +1342,6 @@ static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid)
new->semid = semid;
assert_spin_locked(&ulp->lock);
list_add_rcu(&new->list_proc, &ulp->list_proc);
- assert_spin_locked(&sma->sem_perm.lock);
list_add(&new->list_id, &sma->list_id);
un = new;

@@ -1696,7 +1692,6 @@ void exit_sem(struct task_struct *tsk)
}

/* remove un from the linked lists */
- assert_spin_locked(&sma->sem_perm.lock);
list_del(&un->list_id);

spin_lock(&ulp->lock);
diff --git a/ipc/shm.c b/ipc/shm.c
index cb858df..62b9f1d 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -141,7 +141,7 @@ static inline struct shmid_kernel *shm_lock(struct ipc_namespace *ns, int id)
static inline void shm_lock_by_ptr(struct shmid_kernel *ipcp)
{
rcu_read_lock();
- spin_lock(&ipcp->shm_perm.lock);
+ write_lock(&ipcp->shm_perm.lock);
}

static inline struct shmid_kernel *shm_lock_check(struct ipc_namespace *ns,
diff --git a/ipc/util.c b/ipc/util.c
index 6a98e62..8a87900 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -263,17 +263,17 @@ int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)

idr_preload(GFP_KERNEL);

- spin_lock_init(&new->lock);
+ rwlock_init(&new->lock);
new->deleted = 0;
rcu_read_lock();
- spin_lock(&new->lock);
+ write_lock(&new->lock);

id = idr_alloc(&ids->ipcs_idr, new,
(next_id < 0) ? 0 : ipcid_to_idx(next_id), 0,
GFP_NOWAIT);
idr_preload_end();
if (id < 0) {
- spin_unlock(&new->lock);
+ write_unlock(&new->lock);
rcu_read_unlock();
return id;
}
@@ -708,7 +708,7 @@ struct kern_ipc_perm *ipc_lock(struct ipc_ids *ids, int id)
if (IS_ERR(out))
goto err1;

- spin_lock(&out->lock);
+ write_lock(&out->lock);

/* ipc_rmid() may have already freed the ID while ipc_lock
* was spinning: here verify that the structure is still valid
@@ -718,7 +718,7 @@ struct kern_ipc_perm *ipc_lock(struct ipc_ids *ids, int id)

return out;
err0:
- spin_unlock(&out->lock);
+ write_unlock(&out->lock);
err1:
rcu_read_unlock();
return ERR_PTR(-EINVAL);
@@ -830,7 +830,7 @@ struct kern_ipc_perm *ipcctl_pre_down(struct ipc_namespace *ns,
if (IS_ERR(ipcp))
goto out;

- spin_lock(&ipcp->lock);
+ write_lock(&ipcp->lock);
out:
return ipcp;
}
diff --git a/ipc/util.h b/ipc/util.h
index c36b997..6f157ab 100644
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -162,18 +162,18 @@ static inline int ipc_checkid(struct kern_ipc_perm *ipcp, int uid)
static inline void ipc_lock_by_ptr(struct kern_ipc_perm *perm)
{
rcu_read_lock();
- spin_lock(&perm->lock);
+ write_lock(&perm->lock);
}

static inline void ipc_unlock(struct kern_ipc_perm *perm)
{
- spin_unlock(&perm->lock);
+ write_unlock(&perm->lock);
rcu_read_unlock();
}

static inline void ipc_lock_object(struct kern_ipc_perm *perm)
{
- spin_lock(&perm->lock);
+ write_lock(&perm->lock);
}

struct kern_ipc_perm *ipc_lock_check(struct ipc_ids *ids, int id);

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