Commit 4c677e2e authored by Vasiliy Kulikov's avatar Vasiliy Kulikov Committed by Linus Torvalds
Browse files

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: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarVasiliy Kulikov <segoon@openwall.com>
Acked-by: default avatarSerge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5774ed01

ipc/shm.c

+28 −33
Original line number Diff line number Diff line
@@ -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)

{
@@ -231,18 +237,15 @@ 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))

		return 0;



	if (shp->shm_creator != current) {

		shm_unlock(shp);

	if (shp->shm_creator != current)

		return 0;

	}



	/*

	 * Mark it as orphaned to destroy the segment when
@@ -255,45 +258,43 @@ 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);

	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);

}
@@ -301,17 +302,11 @@ void shm_destroy_orphaned(struct ipc_namespace *ns) 


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);

	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);

}

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