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shm: optimize locking and ipc_namespace getting 

shm_lock() does a lookup of shm segment in shm_ids(ns).ipcs_idr, which
is redundant as we already know shmid_kernel address.  An actual lock is
also not required for reads until we really want to destroy the segment.

exit_shm() and shm_destroy_orphaned() may avoid the loop by checking
whether there is at least one segment in current ipc_namespace.

The check of nsproxy and ipc_ns against NULL is redundant as exit_shm()
is called from do_exit() before the call to exit_notify(), so the
dereferencing current->nsproxy->ipc_ns is guaranteed to be safe.

Reported-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Vasiliy Kulikov 2011-07-29 03:56:40 +04:00 committed by Linus Torvalds
parent 5774ed014f
commit 4c677e2eef
1 changed files with 28 additions and 33 deletions
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61
ipc/shm.c
View File

@ -131,6 +131,12 @@ static inline struct shmid_kernel *shm_lock(struct ipc_namespace *ns, int id)
return container_of(ipcp, struct shmid_kernel, shm_perm);
}
static inline void shm_lock_by_ptr(struct shmid_kernel *ipcp)
{
rcu_read_lock();
spin_lock(&ipcp->shm_perm.lock);
}
static inline struct shmid_kernel *shm_lock_check(struct ipc_namespace *ns,
int id)
{
@ -231,19 +237,16 @@ static void shm_close(struct vm_area_struct *vma)
up_write(&shm_ids(ns).rw_mutex);
}
/* Called with ns->shm_ids(ns).rw_mutex locked */
static int shm_try_destroy_current(int id, void *p, void *data)
{
struct ipc_namespace *ns = data;
struct shmid_kernel *shp = shm_lock(ns, id);
struct kern_ipc_perm *ipcp = p;
struct shmid_kernel *shp = container_of(ipcp, struct shmid_kernel, shm_perm);
if (IS_ERR(shp))
if (shp->shm_creator != current)
return 0;
if (shp->shm_creator != current) {
shm_unlock(shp);
return 0;
}
/*
* Mark it as orphaned to destroy the segment when
* kernel.shm_rmid_forced is changed.
@ -255,64 +258,56 @@ static int shm_try_destroy_current(int id, void *p, void *data)
* Don't even try to destroy it. If shm_rmid_forced=0 and IPC_RMID
* is not set, it shouldn't be deleted here.
*/
if (!ns->shm_rmid_forced) {
shm_unlock(shp);
if (!ns->shm_rmid_forced)
return 0;
}
if (shm_may_destroy(ns, shp))
if (shm_may_destroy(ns, shp)) {
shm_lock_by_ptr(shp);
shm_destroy(ns, shp);
else
shm_unlock(shp);
}
return 0;
}
/* Called with ns->shm_ids(ns).rw_mutex locked */
static int shm_try_destroy_orphaned(int id, void *p, void *data)
{
struct ipc_namespace *ns = data;
struct shmid_kernel *shp = shm_lock(ns, id);
if (IS_ERR(shp))
return 0;
struct kern_ipc_perm *ipcp = p;
struct shmid_kernel *shp = container_of(ipcp, struct shmid_kernel, shm_perm);
/*
* We want to destroy segments without users and with already
* exit'ed originating process.
*
* As shp->* are changed under rw_mutex, it's safe to skip shp locking.
*/
if (shp->shm_creator != NULL) {
shm_unlock(shp);
if (shp->shm_creator != NULL)
return 0;
}
if (shm_may_destroy(ns, shp))
if (shm_may_destroy(ns, shp)) {
shm_lock_by_ptr(shp);
shm_destroy(ns, shp);
else
shm_unlock(shp);
}
return 0;
}
void shm_destroy_orphaned(struct ipc_namespace *ns)
{
down_write(&shm_ids(ns).rw_mutex);
idr_for_each(&shm_ids(ns).ipcs_idr, &shm_try_destroy_orphaned, ns);
if (&shm_ids(ns).in_use)
idr_for_each(&shm_ids(ns).ipcs_idr, &shm_try_destroy_orphaned, ns);
up_write(&shm_ids(ns).rw_mutex);
}
void exit_shm(struct task_struct *task)
{
struct nsproxy *nsp = task->nsproxy;
struct ipc_namespace *ns;
if (!nsp)
return;
ns = nsp->ipc_ns;
if (!ns)
return;
struct ipc_namespace *ns = task->nsproxy->ipc_ns;
/* Destroy all already created segments, but not mapped yet */
down_write(&shm_ids(ns).rw_mutex);
idr_for_each(&shm_ids(ns).ipcs_idr, &shm_try_destroy_current, ns);
if (&shm_ids(ns).in_use)
idr_for_each(&shm_ids(ns).ipcs_idr, &shm_try_destroy_current, ns);
up_write(&shm_ids(ns).rw_mutex);
}