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ipc,sem: do not hold ipc lock more than necessary
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Instead of holding the ipc lock for permissions and security checks, among
others, only acquire it when necessary.

Some numbers....

1) With Rik's semop-multi.c microbenchmark we can see the following
   results:

Baseline (3.9-rc1):
cpus 4, threads: 256, semaphores: 128, test duration: 30 secs
total operations: 151452270, ops/sec 5048409

+  59.40%            a.out  [kernel.kallsyms]  [k] _raw_spin_lock
+   6.14%            a.out  [kernel.kallsyms]  [k] sys_semtimedop
+   3.84%            a.out  [kernel.kallsyms]  [k] avc_has_perm_flags
+   3.64%            a.out  [kernel.kallsyms]  [k] __audit_syscall_exit
+   2.06%            a.out  [kernel.kallsyms]  [k] copy_user_enhanced_fast_string
+   1.86%            a.out  [kernel.kallsyms]  [k] ipc_lock

With this patchset:
cpus 4, threads: 256, semaphores: 128, test duration: 30 secs
total operations: 273156400, ops/sec 9105213

+  18.54%            a.out  [kernel.kallsyms]  [k] _raw_spin_lock
+  11.72%            a.out  [kernel.kallsyms]  [k] sys_semtimedop
+   7.70%            a.out  [kernel.kallsyms]  [k] ipc_has_perm.isra.21
+   6.58%            a.out  [kernel.kallsyms]  [k] avc_has_perm_flags
+   6.54%            a.out  [kernel.kallsyms]  [k] __audit_syscall_exit
+   4.71%            a.out  [kernel.kallsyms]  [k] ipc_obtain_object_check

2) While on an Oracle swingbench DSS (data mining) workload the
   improvements are not as exciting as with Rik's benchmark, we can see
   some positive numbers.  For an 8 socket machine the following are the
   percentages of %sys time incurred in the ipc lock:

Baseline (3.9-rc1):
100 swingbench users: 8,74%
400 swingbench users: 21,86%
800 swingbench users: 84,35%

With this patchset:
100 swingbench users: 8,11%
400 swingbench users: 19,93%
800 swingbench users: 77,69%

[[email protected]: fix two locking bugs]
[[email protected]: prevent releasing RCU read lock twice in semctl_main]
[[email protected]: coding-style fixes]
Signed-off-by: Davidlohr Bueso <[email protected]>
Signed-off-by: Rik van Riel <[email protected]>
Reviewed-by: Chegu Vinod <[email protected]>
Acked-by: Michel Lespinasse <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Jason Low <[email protected]>
Cc: Emmanuel Benisty <[email protected]>
Cc: Peter Hurley <[email protected]>
Cc: Stanislav Kinsbursky <[email protected]>
Tested-by: Sedat Dilek <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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@torvalds
Davidlohr Bueso authored and torvalds committed May 1, 2013
1 parent 444d0f6 commit 16df367
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Showing 2 changed files with 118 additions and 48 deletions.
161 changes: 113 additions & 48 deletions ipc/sem.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -204,13 +204,34 @@ 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 ERR_CAST(ipcp);

return container_of(ipcp, struct sem_array, sem_perm);
}

static inline struct sem_array *sem_lock_check(struct ipc_namespace *ns,
int id)
{
struct kern_ipc_perm *ipcp = ipc_lock_check(&sem_ids(ns), id);

if (IS_ERR(ipcp))
return (struct sem_array *)ipcp;
return ERR_CAST(ipcp);

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 ERR_CAST(ipcp);

return container_of(ipcp, struct sem_array, sem_perm);
}
Expand All @@ -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);
Expand Down Expand Up @@ -842,18 +873,25 @@ 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);
if (IS_ERR(sma))
return PTR_ERR(sma);
rcu_read_lock();
sma = sem_obtain_object(ns, semid);
if (IS_ERR(sma)) {
err = PTR_ERR(sma);
goto out_unlock;
}
id = sma->sem_perm.id;
} else {
sma = sem_lock_check(ns, semid);
if (IS_ERR(sma))
return PTR_ERR(sma);
id = 0;
rcu_read_lock();
sma = sem_obtain_object_check(ns, semid);
if (IS_ERR(sma)) {
err = PTR_ERR(sma);
goto out_unlock;
}
}

err = -EACCES;
Expand All @@ -864,13 +902,11 @@ 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(p, &tbuf, version))
return -EFAULT;
return id;
Expand All @@ -879,7 +915,7 @@ static int semctl_nolock(struct ipc_namespace *ns, int semid,
return -EINVAL;
}
out_unlock:
sem_unlock(sma);
rcu_read_unlock();
return err;
}

Expand Down Expand Up @@ -947,27 +983,34 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
{
struct sem_array *sma;
struct sem* curr;
int err;
int err, nsems;
ushort fast_sem_io[SEMMSL_FAST];
ushort* sem_io = fast_sem_io;
int nsems;
struct list_head tasks;

sma = sem_lock_check(ns, semid);
if (IS_ERR(sma))
INIT_LIST_HEAD(&tasks);

rcu_read_lock();
sma = sem_obtain_object_check(ns, semid);
if (IS_ERR(sma)) {
rcu_read_unlock();
return PTR_ERR(sma);
}

INIT_LIST_HEAD(&tasks);
nsems = sma->sem_nsems;

err = -EACCES;
if (ipcperms(ns, &sma->sem_perm,
cmd == SETALL ? S_IWUGO : S_IRUGO))
goto out_unlock;
cmd == SETALL ? S_IWUGO : S_IRUGO)) {
rcu_read_unlock();
goto out_wakeup;
}

err = security_sem_semctl(sma, cmd);
if (err)
goto out_unlock;
if (err) {
rcu_read_unlock();
goto out_wakeup;
}

err = -EACCES;
switch (cmd) {
Expand All @@ -977,7 +1020,7 @@ 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) {
Expand All @@ -993,6 +1036,7 @@ 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);
Expand All @@ -1006,7 +1050,8 @@ 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);
Expand Down Expand Up @@ -1053,9 +1098,12 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
/* GETVAL, GETPID, GETNCTN, GETZCNT: fall-through */
}
err = -EINVAL;
if(semnum < 0 || semnum >= nsems)
goto out_unlock;
if (semnum < 0 || semnum >= nsems) {
rcu_read_unlock();
goto out_wakeup;
}

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

switch (cmd) {
Expand All @@ -1072,10 +1120,11 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
err = count_semzcnt(sma,semnum);
goto out_unlock;
}

out_unlock:
sem_unlock(sma);
out_wakeup:
wake_up_sem_queue_do(&tasks);

out_free:
if(sem_io != fast_sem_io)
ipc_free(sem_io, sizeof(ushort)*nsems);
Expand Down Expand Up @@ -1126,29 +1175,35 @@ static int semctl_down(struct ipc_namespace *ns, int semid,
return -EFAULT;
}

ipcp = ipcctl_pre_down(ns, &sem_ids(ns), semid, cmd,
&semid64.sem_perm, 0);
ipcp = ipcctl_pre_down_nolock(ns, &sem_ids(ns), semid, cmd,
&semid64.sem_perm, 0);
if (IS_ERR(ipcp))
return PTR_ERR(ipcp);

sma = container_of(ipcp, struct sem_array, sem_perm);

err = security_sem_semctl(sma, cmd);
if (err)
if (err) {
rcu_read_unlock();
goto out_unlock;
}

switch(cmd){
case IPC_RMID:
ipc_lock_object(&sma->sem_perm);
freeary(ns, ipcp);
goto out_up;
case IPC_SET:
ipc_lock_object(&sma->sem_perm);
err = ipc_update_perm(&semid64.sem_perm, ipcp);
if (err)
goto out_unlock;
sma->sem_ctime = get_seconds();
break;
default:
rcu_read_unlock();
err = -EINVAL;
goto out_up;
}

out_unlock:
Expand Down Expand Up @@ -1277,16 +1332,18 @@ static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid)
spin_unlock(&ulp->lock);
if (likely(un!=NULL))
goto out;
rcu_read_unlock();

/* no undo structure around - allocate one. */
/* step 1: figure out the size of the semaphore array */
sma = sem_lock_check(ns, semid);
if (IS_ERR(sma))
sma = sem_obtain_object_check(ns, semid);
if (IS_ERR(sma)) {
rcu_read_unlock();
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);
Expand Down Expand Up @@ -1421,14 +1478,33 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,

INIT_LIST_HEAD(&tasks);

sma = sem_lock_check(ns, semid);
rcu_read_lock();
sma = sem_obtain_object_check(ns, semid);
if (IS_ERR(sma)) {
if (un)
rcu_read_unlock();
error = PTR_ERR(sma);
goto out_free;
}

error = -EFBIG;
if (max >= sma->sem_nsems) {
rcu_read_unlock();
goto out_wakeup;
}

error = -EACCES;
if (ipcperms(ns, &sma->sem_perm, alter ? S_IWUGO : S_IRUGO)) {
rcu_read_unlock();
goto out_wakeup;
}

error = security_sem_semop(sma, sops, nsops, alter);
if (error) {
rcu_read_unlock();
goto out_wakeup;
}

/*
* semid identifiers are not unique - find_alloc_undo may have
* allocated an undo structure, it was invalidated by an RMID
Expand All @@ -1437,6 +1513,7 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
* "un" itself is guaranteed by rcu.
*/
error = -EIDRM;
ipc_lock_object(&sma->sem_perm);
if (un) {
if (un->semid == -1) {
rcu_read_unlock();
Expand All @@ -1454,18 +1531,6 @@ 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)
Expand Down Expand Up @@ -1568,7 +1633,7 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,

out_unlock_free:
sem_unlock(sma);

out_wakeup:
wake_up_sem_queue_do(&tasks);
out_free:
if(sops != fast_sops)
Expand Down
5 changes: 5 additions & 0 deletions ipc/util.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -171,6 +171,11 @@ static inline void ipc_unlock(struct kern_ipc_perm *perm)
rcu_read_unlock();
}

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

struct kern_ipc_perm *ipc_lock_check(struct ipc_ids *ids, int id);
struct kern_ipc_perm *ipc_obtain_object_check(struct ipc_ids *ids, int id);
int ipcget(struct ipc_namespace *ns, struct ipc_ids *ids,
Expand Down

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