[PATCH 2/2] ipc: semaphores: do not hold ipc lock more thannecessary
From: Davidlohr Bueso
Date: Fri Mar 01 2013 - 19:16:56 EST
Instead of holding the ipc lock for permissions and security
checks, among others, only acquire it when necessary.
Signed-off-by: Davidlohr Bueso <davidlohr.bueso@xxxxxx>
---
ipc/sem.c | 94 ++++++++++++++++++++++++++++++++++++++++++++-------------------
1 file changed, 66 insertions(+), 28 deletions(-)
diff --git a/ipc/sem.c b/ipc/sem.c
index 58d31f1..b74a6f7 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -204,6 +204,16 @@ static inline struct sem_array *sem_lock(struct ipc_namespace *ns, int id)
return container_of(ipcp, struct sem_array, sem_perm);
}
+static inline struct sem_array *sem_obtain_object(struct ipc_namespace *ns, int id)
+{
+ struct kern_ipc_perm *ipcp = ipc_obtain_object(&sem_ids(ns), id);
+
+ if (IS_ERR(ipcp))
+ return (struct sem_array *)ipcp;
+
+ return container_of(ipcp, struct sem_array, sem_perm);
+}
+
static inline struct sem_array *sem_lock_check(struct ipc_namespace *ns,
int id)
{
@@ -215,6 +225,17 @@ static inline struct sem_array *sem_lock_check(struct ipc_namespace *ns,
return container_of(ipcp, struct sem_array, sem_perm);
}
+static inline struct sem_array *sem_obtain_object_check(struct ipc_namespace *ns,
+ int id)
+{
+ struct kern_ipc_perm *ipcp = ipc_obtain_object_check(&sem_ids(ns), id);
+
+ if (IS_ERR(ipcp))
+ return (struct sem_array *)ipcp;
+
+ return container_of(ipcp, struct sem_array, sem_perm);
+}
+
static inline void sem_lock_and_putref(struct sem_array *sma)
{
ipc_lock_by_ptr(&sma->sem_perm);
@@ -234,6 +255,16 @@ static inline void sem_putref(struct sem_array *sma)
ipc_unlock(&(sma)->sem_perm);
}
+/*
+ * Call inside the rcu read section.
+ */
+static inline void sem_getref(struct sem_array *sma)
+{
+ spin_lock(&(sma)->sem_perm.lock);
+ ipc_rcu_getref(sma);
+ ipc_unlock(&(sma)->sem_perm);
+}
+
static inline void sem_rmid(struct ipc_namespace *ns, struct sem_array *s)
{
ipc_rmid(&sem_ids(ns), &s->sem_perm);
@@ -842,18 +873,19 @@ static int semctl_nolock(struct ipc_namespace *ns, int semid,
case SEM_STAT:
{
struct semid64_ds tbuf;
- int id;
+ int id = 0;
+
+ memset(&tbuf, 0, sizeof(tbuf));
if (cmd == SEM_STAT) {
- sma = sem_lock(ns, semid);
+ sma = sem_obtain_object(ns, semid);
if (IS_ERR(sma))
return PTR_ERR(sma);
id = sma->sem_perm.id;
} else {
- sma = sem_lock_check(ns, semid);
+ sma = sem_obtain_object_check(ns, semid);
if (IS_ERR(sma))
return PTR_ERR(sma);
- id = 0;
}
err = -EACCES;
@@ -864,13 +896,11 @@ static int semctl_nolock(struct ipc_namespace *ns, int semid,
if (err)
goto out_unlock;
- memset(&tbuf, 0, sizeof(tbuf));
-
kernel_to_ipc64_perm(&sma->sem_perm, &tbuf.sem_perm);
tbuf.sem_otime = sma->sem_otime;
tbuf.sem_ctime = sma->sem_ctime;
tbuf.sem_nsems = sma->sem_nsems;
- sem_unlock(sma);
+ rcu_read_unlock();
if (copy_semid_to_user (arg.buf, &tbuf, version))
return -EFAULT;
return id;
@@ -879,7 +909,7 @@ static int semctl_nolock(struct ipc_namespace *ns, int semid,
return -EINVAL;
}
out_unlock:
- sem_unlock(sma);
+ rcu_read_unlock();
return err;
}
@@ -894,11 +924,12 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
int nsems;
struct list_head tasks;
- sma = sem_lock_check(ns, semid);
+ INIT_LIST_HEAD(&tasks);
+
+ sma = sem_obtain_object_check(ns, semid);
if (IS_ERR(sma))
return PTR_ERR(sma);
- INIT_LIST_HEAD(&tasks);
nsems = sma->sem_nsems;
err = -EACCES;
@@ -918,7 +949,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
int i;
if(nsems > SEMMSL_FAST) {
- sem_getref_and_unlock(sma);
+ sem_getref(sma);
sem_io = ipc_alloc(sizeof(ushort)*nsems);
if(sem_io == NULL) {
@@ -934,6 +965,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
}
}
+ spin_lock(&sma->sem_perm.lock);
for (i = 0; i < sma->sem_nsems; i++)
sem_io[i] = sma->sem_base[i].semval;
sem_unlock(sma);
@@ -947,7 +979,8 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
int i;
struct sem_undo *un;
- sem_getref_and_unlock(sma);
+ ipc_rcu_getref(sma);
+ rcu_read_unlock();
if(nsems > SEMMSL_FAST) {
sem_io = ipc_alloc(sizeof(ushort)*nsems);
@@ -997,6 +1030,7 @@ 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);
curr = &sma->sem_base[semnum];
switch (cmd) {
@@ -1101,9 +1135,11 @@ static int semctl_down(struct ipc_namespace *ns, int semid,
switch(cmd){
case IPC_RMID:
+ spin_lock(&sma->sem_perm.lock);
freeary(ns, ipcp);
goto out_up;
case IPC_SET:
+ spin_lock(&sma->sem_perm.lock);
err = ipc_update_perm(&semid64.sem_perm, ipcp);
if (err)
goto out_unlock;
@@ -1252,12 +1288,13 @@ static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid)
/* no undo structure around - allocate one. */
/* step 1: figure out the size of the semaphore array */
- sma = sem_lock_check(ns, semid);
+ sma = sem_obtain_object_check(ns, semid);
if (IS_ERR(sma))
return ERR_CAST(sma);
nsems = sma->sem_nsems;
- sem_getref_and_unlock(sma);
+ ipc_rcu_getref(sma);
+ rcu_read_unlock();
/* step 2: allocate new undo structure */
new = kzalloc(sizeof(struct sem_undo) + sizeof(short)*nsems, GFP_KERNEL);
@@ -1392,7 +1429,7 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
INIT_LIST_HEAD(&tasks);
- sma = sem_lock_check(ns, semid);
+ sma = sem_obtain_object_check(ns, semid);
if (IS_ERR(sma)) {
if (un)
rcu_read_unlock();
@@ -1400,6 +1437,18 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
goto out_free;
}
+ error = -EFBIG;
+ if (max >= sma->sem_nsems)
+ goto out_unlock_free;
+
+ error = -EACCES;
+ if (ipcperms(ns, &sma->sem_perm, alter ? S_IWUGO : S_IRUGO))
+ goto out_unlock_free;
+
+ error = security_sem_semop(sma, sops, nsops, alter);
+ if (error)
+ goto out_unlock_free;
+
/*
* semid identifiers are not unique - find_alloc_undo may have
* allocated an undo structure, it was invalidated by an RMID
@@ -1408,6 +1457,7 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
* "un" itself is guaranteed by rcu.
*/
error = -EIDRM;
+ spin_lock(&sma->sem_perm.lock);
if (un) {
if (un->semid == -1) {
rcu_read_unlock();
@@ -1425,18 +1475,6 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
}
}
- error = -EFBIG;
- if (max >= sma->sem_nsems)
- goto out_unlock_free;
-
- error = -EACCES;
- if (ipcperms(ns, &sma->sem_perm, alter ? S_IWUGO : S_IRUGO))
- goto out_unlock_free;
-
- error = security_sem_semop(sma, sops, nsops, alter);
- if (error)
- goto out_unlock_free;
-
error = try_atomic_semop (sma, sops, nsops, un, task_tgid_vnr(current));
if (error <= 0) {
if (alter && error == 0)
@@ -1476,8 +1514,8 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
queue.sleeper = current;
sleep_again:
- current->state = TASK_INTERRUPTIBLE;
sem_unlock(sma);
+ current->state = TASK_INTERRUPTIBLE;
if (timeout)
jiffies_left = schedule_timeout(jiffies_left);
--
1.7.11.7
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