[Devel] Re: [PATCH 2/2] Add support for the per-task sem_undo list (v2)
Dan Smith
danms at us.ibm.com
Thu Aug 5 09:17:31 PDT 2010
OL> Deal :)
Okay, included below. I put the refcount for the first task before
the "out:" label to avoid the curly braces on the else clause, which
should be functionally the same. Hope that's okay :)
Thanks!
--
Dan Smith
IBM Linux Technology Center
email: danms at us.ibm.com
Add support for the per-task sem_undo list (v3)
The semaphore undo list is a set of adjustments to be made to semaphores
held by a task on exit. Right now, we do not checkpoint or restore this
list which could cause undesirable behavior by a restarted process on exit.
Changes in v3:
- Move taking of the refcount for the first process to restore_sem_undo()
and make restore_obj_sem_undo() take the reference for second-and-
later tasks
- Fix uses of __u16 to represent a short
- Fix potential for overrunning the un->semadj buffer in restore
- Move the checkpoint object and init functions to the bottom of sem.c
Changes in v2:
- Remove collect operation
- Add a BUILD_BUG_ON() to ensure sizeof(short) == sizeof(__u16)
- Use sizeof(__u16) when copying to/from checkpoint header
- Fix a couple of leaked hdr objects
- Avoid reading the semadj buffer with rcu_read_lock() held
- Set the sem_undo pointer on tasks other than the first to restore a list
- Fix refcounting on restart
- Pull out the guts of exit_sem() into put_undo_list() and call that
from our drop() function in case we're the last one.
Signed-off-by: Dan Smith <danms at us.ibm.com>
diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
index 4e25042..a11d40e 100644
--- a/include/linux/checkpoint.h
+++ b/include/linux/checkpoint.h
@@ -271,6 +271,10 @@ extern int ckpt_collect_fs(struct ckpt_ctx *ctx, struct task_struct *t);
extern int checkpoint_obj_fs(struct ckpt_ctx *ctx, struct task_struct *t);
extern int restore_obj_fs(struct ckpt_ctx *ctx, int fs_objref);
+/* per-task semaphore undo */
+extern int checkpoint_obj_sem_undo(struct ckpt_ctx *ctx, struct task_struct *t);
+extern int restore_obj_sem_undo(struct ckpt_ctx *ctx, int sem_undo_objref);
+
/* memory */
extern void ckpt_pgarr_free(struct ckpt_ctx *ctx);
diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
index f4f9577..b48fa37 100644
--- a/include/linux/checkpoint_hdr.h
+++ b/include/linux/checkpoint_hdr.h
@@ -167,6 +167,10 @@ enum {
#define CKPT_HDR_IPC_MSG_MSG CKPT_HDR_IPC_MSG_MSG
CKPT_HDR_IPC_SEM,
#define CKPT_HDR_IPC_SEM CKPT_HDR_IPC_SEM
+ CKPT_HDR_TASK_SEM_UNDO_LIST,
+#define CKPT_HDR_TASK_SEM_UNDO_LIST CKPT_HDR_TASK_SEM_UNDO_LIST
+ CKPT_HDR_TASK_SEM_UNDO,
+#define CKPT_HDR_TASK_SEM_UNDO CKPT_HDR_TASK_SEM_UNDO
CKPT_HDR_SIGHAND = 601,
#define CKPT_HDR_SIGHAND CKPT_HDR_SIGHAND
@@ -273,6 +277,8 @@ enum obj_type {
#define CKPT_OBJ_NET_NS CKPT_OBJ_NET_NS
CKPT_OBJ_NETDEV,
#define CKPT_OBJ_NETDEV CKPT_OBJ_NETDEV
+ CKPT_OBJ_SEM_UNDO,
+#define CKPT_OBJ_SEM_UNDO CKPT_OBJ_SEM_UNDO
CKPT_OBJ_MAX
#define CKPT_OBJ_MAX CKPT_OBJ_MAX
};
@@ -461,6 +467,17 @@ struct ckpt_hdr_ns {
__s32 net_objref;
} __attribute__((aligned(8)));
+struct ckpt_hdr_task_sem_undo_list {
+ struct ckpt_hdr h;
+ __u32 count;
+};
+
+struct ckpt_hdr_task_sem_undo {
+ struct ckpt_hdr h;
+ __u32 semid;
+ __u32 semadj_count;
+};
+
/* cannot include <linux/tty.h> from userspace, so define: */
#define CKPT_NEW_UTS_LEN 64
#ifdef __KERNEL__
@@ -487,6 +504,7 @@ struct ckpt_hdr_task_objs {
__s32 files_objref;
__s32 mm_objref;
__s32 fs_objref;
+ __s32 sem_undo_objref;
__s32 sighand_objref;
__s32 signal_objref;
} __attribute__((aligned(8)));
diff --git a/ipc/sem.c b/ipc/sem.c
index e439b73..d79b1ee 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -132,14 +132,6 @@ void sem_exit_ns(struct ipc_namespace *ns)
}
#endif
-void __init sem_init (void)
-{
- sem_init_ns(&init_ipc_ns);
- ipc_init_proc_interface("sysvipc/sem",
- " key semid perms nsems uid gid cuid cgid otime ctime\n",
- IPC_SEM_IDS, sysvipc_sem_proc_show);
-}
-
/*
* sem_lock_(check_) routines are called in the paths where the rw_mutex
* is not held.
@@ -1363,14 +1355,8 @@ int copy_semundo(unsigned long clone_flags, struct task_struct *tsk)
* The current implementation does not do so. The POSIX standard
* and SVID should be consulted to determine what behavior is mandated.
*/
-void exit_sem(struct task_struct *tsk)
+static void put_undo_list(struct sem_undo_list *ulp)
{
- struct sem_undo_list *ulp;
-
- ulp = tsk->sysvsem.undo_list;
- if (!ulp)
- return;
- tsk->sysvsem.undo_list = NULL;
if (!atomic_dec_and_test(&ulp->refcnt))
return;
@@ -1393,7 +1379,7 @@ void exit_sem(struct task_struct *tsk)
if (semid == -1)
break;
- sma = sem_lock_check(tsk->nsproxy->ipc_ns, un->semid);
+ sma = sem_lock_check(ulp->ipc_ns, un->semid);
/* exit_sem raced with IPC_RMID, nothing to do */
if (IS_ERR(sma))
@@ -1451,6 +1437,16 @@ void exit_sem(struct task_struct *tsk)
kfree(ulp);
}
+void exit_sem(struct task_struct *tsk)
+{
+ struct sem_undo_list *ulp = tsk->sysvsem.undo_list;
+
+ if (ulp) {
+ put_undo_list(ulp);
+ tsk->sysvsem.undo_list = NULL;
+ }
+}
+
#ifdef CONFIG_PROC_FS
static int sysvipc_sem_proc_show(struct seq_file *s, void *it)
{
@@ -1470,3 +1466,324 @@ static int sysvipc_sem_proc_show(struct seq_file *s, void *it)
sma->sem_ctime);
}
#endif
+
+static int __get_task_semids(struct sem_undo_list *ulp, int *semids, int max)
+{
+ int count = 0;
+ struct sem_undo *un;
+
+ if (!ulp)
+ return 0;
+
+ spin_lock(&ulp->lock);
+ list_for_each_entry_rcu(un, &ulp->list_proc, list_proc) {
+ if (count >= max) {
+ count = -E2BIG;
+ break;
+ }
+ semids[count++] = un->semid;
+ }
+ spin_unlock(&ulp->lock);
+
+ return count;
+}
+
+static int get_task_semids(struct sem_undo_list *ulp, int **semid_listp)
+{
+ int ret;
+ int max = 32;
+ int *semid_list = NULL;
+ retry:
+ *semid_listp = krealloc(semid_list, max * sizeof(int), GFP_KERNEL);
+ if (!*semid_listp) {
+ kfree(semid_list);
+ return -ENOMEM;
+ }
+ semid_list = *semid_listp;
+
+ ret = __get_task_semids(ulp, semid_list, max);
+ if (ret == -E2BIG) {
+ max *= 2;
+ goto retry;
+ } else if (ret < 0) {
+ kfree(semid_list);
+ *semid_listp = NULL;
+ }
+
+ return ret;
+}
+
+int checkpoint_sem_undo_adj(struct ckpt_ctx *ctx, struct sem_undo *un)
+{
+ int nsems;
+ int ret;
+ short *semadj = NULL;
+ struct sem_array *sma;
+ struct ckpt_hdr_task_sem_undo *h = NULL;
+
+ sma = sem_lock(ctx->root_nsproxy->ipc_ns, un->semid);
+ if (IS_ERR(sma)) {
+ ckpt_debug("unable to lock semid %i (wrong ns?)\n", un->semid);
+ return PTR_ERR(sma);
+ }
+
+ nsems = sma->sem_nsems;
+ sem_getref_and_unlock(sma);
+
+ h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_TASK_SEM_UNDO);
+ if (!h)
+ goto putref_abort;
+
+ semadj = kzalloc(nsems * sizeof(short), GFP_KERNEL);
+ if (!semadj)
+ goto putref_abort;
+
+ sem_lock_and_putref(sma);
+
+ h->semid = un->semid;
+ h->semadj_count = nsems;
+ memcpy(semadj, un->semadj, h->semadj_count * sizeof(__s16));
+
+ sem_unlock(sma);
+
+ ret = ckpt_write_obj(ctx, (struct ckpt_hdr *)h);
+ if (ret == 0)
+ ret = ckpt_write_buffer(ctx, semadj, nsems * sizeof(__s16));
+
+ kfree(semadj);
+ ckpt_hdr_put(ctx, h);
+
+ return ret;
+
+ putref_abort:
+ sem_putref(sma);
+ if (h)
+ ckpt_hdr_put(ctx, h);
+
+ return -ENOMEM;
+}
+
+int write_sem_undo_list(struct ckpt_ctx *ctx, struct sem_undo_list *ulp,
+ int count, int *semids)
+{
+ int i;
+ int ret;
+
+ for (i = 0; i < count; i++) {
+ struct sem_undo *un;
+
+ spin_lock(&ulp->lock);
+ un = lookup_undo(ulp, semids[i]);
+ spin_unlock(&ulp->lock);
+
+ if (!un) {
+ ckpt_debug("unable to lookup semid %i\n", semids[i]);
+ return -EINVAL;
+ }
+
+ ret = checkpoint_sem_undo_adj(ctx, un);
+ ckpt_debug("checkpoint_sem_undo: %i\n", ret);
+ if (ret < 0)
+ return ret;
+ }
+
+ return 0;
+}
+
+static int checkpoint_sem_undo(struct ckpt_ctx *ctx, void *ptr)
+{
+ int ret;
+ int *semids = NULL;
+ struct sem_undo_list *ulp = ptr;
+ struct ckpt_hdr_task_sem_undo_list *h;
+
+ h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_TASK_SEM_UNDO_LIST);
+ if (!h)
+ return -ENOMEM;
+
+ ret = get_task_semids(ulp, &semids);
+ if (ret < 0)
+ goto out;
+ h->count = ret;
+
+ ret = ckpt_write_obj(ctx, (struct ckpt_hdr *)h);
+ if (ret < 0)
+ goto out;
+
+ ret = write_sem_undo_list(ctx, ulp, h->count, semids);
+ out:
+ ckpt_hdr_put(ctx, h);
+ kfree(semids);
+
+ return ret;
+}
+
+int checkpoint_obj_sem_undo(struct ckpt_ctx *ctx, struct task_struct *t)
+{
+ struct sem_undo_list *ulp;
+
+ ulp = t->sysvsem.undo_list;
+ if (ulp)
+ return checkpoint_obj(ctx, ulp, CKPT_OBJ_SEM_UNDO);
+
+ return 0;
+}
+
+/* Count the number of sems for the given sem_undo->semid */
+static int sem_undo_nsems(struct sem_undo *un, struct ipc_namespace *ns)
+{
+ struct sem_array *sma;
+ int nsems;
+
+ sma = sem_lock(ns, un->semid);
+ if (IS_ERR(sma))
+ return PTR_ERR(sma);
+
+ nsems = sma->sem_nsems;
+ sem_unlock(sma);
+
+ return nsems;
+}
+
+static int restore_task_sem_undo_adj(struct ckpt_ctx *ctx)
+{
+ struct ckpt_hdr_task_sem_undo *h;
+ int len;
+ int ret = -ENOMEM;
+ struct sem_undo *un;
+ int nsems;
+ short *semadj = NULL;
+
+ h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_TASK_SEM_UNDO);
+ if (IS_ERR(h))
+ return PTR_ERR(h);
+
+ len = sizeof(__s16) * h->semadj_count;
+ semadj = kzalloc(len, GFP_KERNEL);
+ if (!semadj)
+ goto out;
+
+ ret = _ckpt_read_buffer(ctx, semadj, len);
+ if (ret < 0)
+ goto out;
+
+ un = find_alloc_undo(current->nsproxy->ipc_ns, h->semid);
+ if (IS_ERR(un)) {
+ ret = PTR_ERR(un);
+ ckpt_debug("unable to find semid %i\n", h->semid);
+ goto out;
+ }
+
+ nsems = sem_undo_nsems(un, current->nsproxy->ipc_ns);
+ len = sizeof(__s16) * nsems;
+ if (h->semadj_count == nsems)
+ memcpy(un->semadj, semadj, len);
+ rcu_read_unlock();
+
+ if (nsems != h->semadj_count)
+ ckpt_err(ctx, -EINVAL,
+ "semid %i has nmsems=%i but %i undo adjustments\n",
+ h->semid, nsems, h->semadj_count);
+ else
+ ckpt_debug("semid %i restored with %i adjustments\n",
+ h->semid, h->semadj_count);
+ out:
+ ckpt_hdr_put(ctx, h);
+ kfree(semadj);
+
+ return ret;
+}
+
+static void *restore_sem_undo(struct ckpt_ctx *ctx)
+{
+ struct ckpt_hdr_task_sem_undo_list *h;
+ struct sem_undo_list *ulp = NULL;
+ int i;
+ int ret = 0;
+
+ h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_TASK_SEM_UNDO_LIST);
+ if (IS_ERR(h))
+ return ERR_PTR(PTR_ERR(h));
+
+ ulp = alloc_undo_list(current->nsproxy->ipc_ns);
+ if (!ulp) {
+ ret = -ENOMEM;
+ goto out;
+ }
+
+ for (i = 0; i < h->count; i++) {
+ ret = restore_task_sem_undo_adj(ctx);
+ if (ret < 0)
+ goto out;
+ }
+
+ atomic_inc(&ulp->refcnt);
+ out:
+ ckpt_hdr_put(ctx, h);
+ if (ret < 0)
+ return ERR_PTR(ret);
+ else
+ return ulp;
+}
+
+int restore_obj_sem_undo(struct ckpt_ctx *ctx, int sem_undo_objref)
+{
+ struct sem_undo_list *ulp;
+
+ if (!sem_undo_objref)
+ return 0; /* Task had no undo list */
+
+ ulp = ckpt_obj_try_fetch(ctx, sem_undo_objref, CKPT_OBJ_SEM_UNDO);
+ if (IS_ERR(ulp))
+ return PTR_ERR(ulp);
+
+ /* The first task to restore a shared list should already have this,
+ * but subsequent ones won't, so attach to current in that case and
+ * take our reference.
+ */
+ if (!current->sysvsem.undo_list) {
+ current->sysvsem.undo_list = ulp;
+ atomic_inc(&ulp->refcnt);
+ }
+
+ return 0;
+}
+
+static int obj_sem_undo_grab(void *ptr)
+{
+ struct sem_undo_list *ulp = ptr;
+
+ atomic_inc(&ulp->refcnt);
+ return 0;
+}
+
+static void obj_sem_undo_drop(void *ptr, int lastref)
+{
+ struct sem_undo_list *ulp = ptr;
+
+ put_undo_list(ulp);
+}
+
+static const struct ckpt_obj_ops ckpt_obj_sem_undo_ops = {
+ .obj_name = "IPC_SEM_UNDO",
+ .obj_type = CKPT_OBJ_SEM_UNDO,
+ .ref_drop = obj_sem_undo_drop,
+ .ref_grab = obj_sem_undo_grab,
+ .checkpoint = checkpoint_sem_undo,
+ .restore = restore_sem_undo,
+};
+
+void __init sem_init (void)
+{
+ sem_init_ns(&init_ipc_ns);
+ ipc_init_proc_interface("sysvipc/sem",
+ " key semid perms nsems uid gid cuid cgid otime ctime\n",
+ IPC_SEM_IDS, sysvipc_sem_proc_show);
+
+ /* sem_undo_list uses a short
+ * ckpt_hdr_task_sem_undo uses a __s16
+ */
+ BUILD_BUG_ON(sizeof(short) != sizeof(__s16));
+
+ register_checkpoint_obj(&ckpt_obj_sem_undo_ops);
+}
diff --git a/kernel/checkpoint/process.c b/kernel/checkpoint/process.c
index 936675a..4ec9cdd 100644
--- a/kernel/checkpoint/process.c
+++ b/kernel/checkpoint/process.c
@@ -236,6 +236,7 @@ static int checkpoint_task_objs(struct ckpt_ctx *ctx, struct task_struct *t)
int files_objref;
int mm_objref;
int fs_objref;
+ int sem_undo_objref;
int sighand_objref;
int signal_objref;
int first, ret;
@@ -283,6 +284,12 @@ static int checkpoint_task_objs(struct ckpt_ctx *ctx, struct task_struct *t)
return fs_objref;
}
+ sem_undo_objref = checkpoint_obj_sem_undo(ctx, t);
+ if (sem_undo_objref < 0) {
+ ckpt_err(ctx, sem_undo_objref, "%(T)process sem_undo\n");
+ return sem_undo_objref;
+ }
+
sighand_objref = checkpoint_obj_sighand(ctx, t);
ckpt_debug("sighand: objref %d\n", sighand_objref);
if (sighand_objref < 0) {
@@ -311,6 +318,7 @@ static int checkpoint_task_objs(struct ckpt_ctx *ctx, struct task_struct *t)
h->files_objref = files_objref;
h->mm_objref = mm_objref;
h->fs_objref = fs_objref;
+ h->sem_undo_objref = sem_undo_objref;
h->sighand_objref = sighand_objref;
h->signal_objref = signal_objref;
ret = ckpt_write_obj(ctx, &h->h);
@@ -679,6 +687,11 @@ static int restore_task_objs(struct ckpt_ctx *ctx)
if (ret < 0)
return ret;
+ ret = restore_obj_sem_undo(ctx, h->sem_undo_objref);
+ ckpt_debug("sem_undo: ret %d\n", ret);
+ if (ret < 0)
+ return ret;
+
ret = restore_obj_sighand(ctx, h->sighand_objref);
ckpt_debug("sighand: ret %d (%p)\n", ret, current->sighand);
if (ret < 0)
_______________________________________________
Containers mailing list
Containers at lists.linux-foundation.org
https://lists.linux-foundation.org/mailman/listinfo/containers
More information about the Devel
mailing list