Skip to content

Commit

Permalink
ipc,sem: do not hold ipc lock more than necessary
Browse files Browse the repository at this point in the history 
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%

[riel@redhat.com: fix two locking bugs]
[sasha.levin@oracle.com: prevent releasing RCU read lock twice in semctl_main]
[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Signed-off-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Chegu Vinod <chegu_vinod@hp.com>
Acked-by: Michel Lespinasse <walken@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Jason Low <jason.low2@hp.com>
Cc: Emmanuel Benisty <benisty.e@gmail.com>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Stanislav Kinsbursky <skinsbursky@parallels.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  • Loading branch information
Davidlohr Bueso authored and Linus Torvalds committed May 1, 2013
1 parent 444d0f6 commit 16df367
Show file tree
Hide file tree
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

0 comments on commit 16df367

Please sign in to comment.