diff options
author | Vasiliy Kulikov <segoon@openwall.com> | 2011-07-29 01:56:40 +0200 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2011-07-30 20:44:20 +0200 |
commit | 4c677e2eefdba9c5bfc4474e2e91b26ae8458a1d (patch) | |
tree | c3c81703d022e0c3c43ddffc3ae165eb25aa0b1d /ipc | |
parent | shm: handle separate PID namespaces case (diff) | |
download | linux-4c677e2eefdba9c5bfc4474e2e91b26ae8458a1d.tar.xz linux-4c677e2eefdba9c5bfc4474e2e91b26ae8458a1d.zip |
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>
Diffstat (limited to 'ipc')
-rw-r--r-- | ipc/shm.c | 61 |
1 files changed, 28 insertions, 33 deletions
diff --git a/ipc/shm.c b/ipc/shm.c index fdaf8be65b75..9fb044f3b345 100644 --- a/ipc/shm.c +++ b/ipc/shm.c @@ -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 @@ -255,64 +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); } |