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Subject[PATCH v21 067/100] c/r: [signal 3/4] pending signals (private, shared)
Date
This patch adds checkpoint and restart of pending signals queues:
struct sigpending, both per-task t->sigpending and shared (per-
thread-group) t->signal->shared_sigpending.

To checkpoint pending signals (private/shared) we first detach the
signal queue (and copy the mask) to a separate struct sigpending.
This separate structure can be iterated through without locking.

Once the state is saved, we re-attaches (prepends) the original signal
queue back to the original struct sigpending.

Signals that arrive(d) in the meantime will be suitably queued after
these (for real-time signals). Repeated non-realtime signals will not
be queued because they will already be marked in the pending mask,
that remains as is. This is the expected behavior of non-realtime
signals.

Changelog[v21]:
- [Matt Helsley] Move the signal c/r changes to kernel/signal.c
Changelog [v19-rc1]:
- Switch to ckpt_obj_try_fetch()
- [Matt Helsley] Add cpp definitions for enums
Changelog [v4]:
- Rename headerless struct ckpt_hdr_* to struct ckpt_*
Changelog [v3]:
- [Dan Smith] Sanity check for number of pending signals in buffer
Changelog [v2]:
- Validate si_errno from checkpoint image
Changelog [v1]:
- Fix compilation warnings
- [Louis Rilling] Remove SIGQUEUE_PREALLOC flag from queued signals
- [Louis Rilling] Fail if task has posix-timers or SI_TIMER signal

Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Oren Laadan <orenl@cs.columbia.edu>
Acked-by: Louis Rilling <Louis.Rilling@kerlabs.com>
Acked-by: Serge E. Hallyn <serue@us.ibm.com>
Tested-by: Serge E. Hallyn <serue@us.ibm.com>
---
include/linux/checkpoint_hdr.h | 24 ++++
kernel/signal.c | 279 +++++++++++++++++++++++++++++++++++++++-
2 files changed, 301 insertions(+), 2 deletions(-)
diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
index 0320bfa..3e6b49b 100644
--- a/include/linux/checkpoint_hdr.h
+++ b/include/linux/checkpoint_hdr.h
@@ -142,6 +142,8 @@ enum {
#define CKPT_HDR_SIGNAL CKPT_HDR_SIGNAL
CKPT_HDR_SIGNAL_TASK,
#define CKPT_HDR_SIGNAL_TASK CKPT_HDR_SIGNAL_TASK
+ CKPT_HDR_SIGPENDING,
+#define CKPT_HDR_SIGPENDING CKPT_HDR_SIGPENDING

CKPT_HDR_TAIL = 9001,
#define CKPT_HDR_TAIL CKPT_HDR_TAIL
@@ -545,6 +547,28 @@ struct ckpt_hdr_sighand {
struct ckpt_sigaction action[0];
} __attribute__((aligned(8)));

+#ifndef HAVE_ARCH_SIGINFO_T
+struct ckpt_siginfo {
+ __u32 signo;
+ __u32 _errno;
+ __u32 code;
+
+ __u32 pid;
+ __s32 uid;
+ __u32 sigval_int;
+ __u64 sigval_ptr;
+ __u64 utime;
+ __u64 stime;
+} __attribute__((aligned(8)));
+#endif
+
+struct ckpt_hdr_sigpending {
+ struct ckpt_hdr h;
+ __u32 nr_pending;
+ struct ckpt_sigset signal;
+ struct ckpt_siginfo siginfo[0];
+} __attribute__((aligned(8)));
+
struct ckpt_rlimit {
__u64 rlim_cur;
__u64 rlim_max;
diff --git a/kernel/signal.c b/kernel/signal.c
index aae1f73..11f54ad 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2911,11 +2911,155 @@ static const struct ckpt_obj_ops ckpt_obj_sighand_ops = {
* signal checkpoint/restart
*/

+static void fill_siginfo(struct ckpt_siginfo *si, siginfo_t *info)
+{
+ si->signo = info->si_signo;
+ si->_errno = info->si_errno;
+ si->code = info->si_code;
+
+ /* TODO: convert info->si_uid to uid_objref */
+
+ switch (info->si_code & __SI_MASK) {
+ case __SI_TIMER:
+ si->pid = info->si_tid;
+ si->uid = info->si_overrun;
+ si->sigval_int = info->si_int;
+ si->utime = info->si_sys_private;
+ break;
+ case __SI_POLL:
+ si->pid = info->si_band;
+ si->sigval_int = info->si_fd;
+ break;
+ case __SI_FAULT:
+ si->sigval_ptr = (unsigned long) info->si_addr;
+#ifdef __ARCH_SI_TRAPNO
+ si->sigval_int = info->si_trapno;
+#endif
+ break;
+ case __SI_CHLD:
+ si->pid = info->si_pid;
+ si->uid = info->si_uid;
+ si->sigval_int = info->si_status;
+ si->stime = info->si_stime;
+ si->utime = info->si_utime;
+ break;
+ case __SI_KILL:
+ case __SI_RT:
+ case __SI_MESGQ:
+ si->pid = info->si_pid;
+ si->uid = info->si_uid;
+ si->sigval_ptr = (unsigned long) info->si_ptr;
+ break;
+ default:
+ BUG();
+ }
+}
+
+static int load_siginfo(siginfo_t *info, struct ckpt_siginfo *si)
+{
+ if (!valid_signal(si->signo))
+ return -EINVAL;
+ if (!ckpt_validate_errno(si->_errno))
+ return -EINVAL;
+
+ info->si_signo = si->signo;
+ info->si_errno = si->_errno;
+ info->si_code = si->code;
+
+ /* TODO: validate remaining signal fields */
+
+ switch (info->si_code & __SI_MASK) {
+ case __SI_TIMER:
+ info->si_tid = si->pid;
+ info->si_overrun = si->uid;
+ info->si_int = si->sigval_int;
+ info->si_sys_private = si->utime;
+ break;
+ case __SI_POLL:
+ info->si_band = si->pid;
+ info->si_fd = si->sigval_int;
+ break;
+ case __SI_FAULT:
+ info->si_addr = (void __user *) (unsigned long) si->sigval_ptr;
+#ifdef __ARCH_SI_TRAPNO
+ info->si_trapno = si->sigval_int;
+#endif
+ break;
+ case __SI_CHLD:
+ info->si_pid = si->pid;
+ info->si_uid = si->uid;
+ info->si_status = si->sigval_int;
+ info->si_stime = si->stime;
+ info->si_utime = si->utime;
+ break;
+ case __SI_KILL:
+ case __SI_RT:
+ case __SI_MESGQ:
+ info->si_pid = si->pid;
+ info->si_uid = si->uid;
+ info->si_ptr = (void __user *) (unsigned long) si->sigval_ptr;
+ break;
+ default:
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
+/*
+ * To checkpoint pending signals (private/shared) the caller moves the
+ * signal queue (and copies the mask) to a separate struct sigpending,
+ * therefore we can iterate through it without locking.
+ * After we return, the caller re-attaches (prepends) the original
+ * signal queue to the original struct sigpending. Thus, signals that
+ * arrive(d) in the meantime will be suitably queued after these.
+ * Finally, repeated non-realtime signals will not be queued because
+ * they will already be marked in the pending mask, that remains as is.
+ * This is the expected behavior of non-realtime signals.
+ */
+static int checkpoint_sigpending(struct ckpt_ctx *ctx,
+ struct sigpending *pending)
+{
+ struct ckpt_hdr_sigpending *h;
+ struct ckpt_siginfo *si;
+ struct sigqueue *q;
+ int nr_pending = 0;
+ int ret;
+
+ list_for_each_entry(q, &pending->list, list) {
+ /* TODO: remove after adding support for posix-timers */
+ if ((q->info.si_code & __SI_MASK) == __SI_TIMER) {
+ ckpt_err(ctx, -ENOTSUPP, "%(T)signal SI_TIMER\n");
+ return -ENOTSUPP;
+ }
+ nr_pending++;
+ }
+
+ h = ckpt_hdr_get_type(ctx, nr_pending * sizeof(*si) + sizeof(*h),
+ CKPT_HDR_SIGPENDING);
+ if (!h)
+ return -ENOMEM;
+
+ h->nr_pending = nr_pending;
+ fill_sigset(&h->signal, &pending->signal);
+
+ si = h->siginfo;
+ list_for_each_entry(q, &pending->list, list)
+ fill_siginfo(si++, &q->info);
+
+ ret = ckpt_write_obj(ctx, &h->h);
+ ckpt_hdr_put(ctx, h);
+
+ return ret;
+}
+
static int checkpoint_signal(struct ckpt_ctx *ctx, struct task_struct *t)
{
struct ckpt_hdr_signal *h;
struct signal_struct *signal;
+ struct sigpending shared_pending;
struct rlimit *rlim;
+ unsigned long flags;
int i, ret;

h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_SIGNAL);
@@ -2925,13 +3069,46 @@ static int checkpoint_signal(struct ckpt_ctx *ctx, struct task_struct *t)
signal = t->signal;
rlim = signal->rlim;

+ INIT_LIST_HEAD(&shared_pending.list);
+
+ /* temporarily borrow signal queue - see chekcpoint_sigpending() */
+ if (!lock_task_sighand(t, &flags)) {
+ ckpt_err(ctx, -EBUSY, "%(T)c/r: [pid %d] without sighand\n",
+ task_pid_vnr(t));
+ ret = -EBUSY;
+ goto out;
+ }
+
+ /* TODO: remove after adding support for posix-timers */
+ if (!list_empty(&signal->posix_timers)) {
+ unlock_task_sighand(t, &flags);
+ ckpt_err(ctx, -ENOTSUPP, "%(T)%(P)posix-timers\n", signal);
+ ret = -ENOTSUPP;
+ goto out;
+ }
+
+ list_splice_init(&signal->shared_pending.list, &shared_pending.list);
+ shared_pending.signal = signal->shared_pending.signal;
+
/* rlimit */
for (i = 0; i < RLIM_NLIMITS; i++) {
h->rlim[i].rlim_cur = rlim[i].rlim_cur;
h->rlim[i].rlim_max = rlim[i].rlim_max;
}
+ unlock_task_sighand(t, &flags);

ret = ckpt_write_obj(ctx, &h->h);
+ if (!ret)
+ ret = checkpoint_sigpending(ctx, &shared_pending);
+
+ /* return the borrowed queue */
+ if (!lock_task_sighand(t, &flags)) {
+ pr_warning("c/r: [%d] sighand disappeared\n", task_pid_vnr(t));
+ goto out;
+ }
+ list_splice(&shared_pending.list, &signal->shared_pending.list);
+ unlock_task_sighand(t, &flags);
+ out:
ckpt_hdr_put(ctx, h);
return ret;
}
@@ -2942,9 +3119,55 @@ int checkpoint_obj_signal(struct ckpt_ctx *ctx, struct task_struct *t)
return checkpoint_signal(ctx, t);
}

+static int restore_sigpending(struct ckpt_ctx *ctx, struct sigpending *pending)
+{
+ struct ckpt_hdr_sigpending *h;
+ struct ckpt_siginfo *si;
+ struct sigqueue *q;
+ int ret = 0;
+
+ h = ckpt_read_buf_type(ctx, 0, CKPT_HDR_SIGPENDING);
+ if (IS_ERR(h))
+ return PTR_ERR(h);
+
+ if (h->h.len != h->nr_pending * sizeof(*si) + sizeof(*h)) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ INIT_LIST_HEAD(&pending->list);
+ load_sigset(&pending->signal, &h->signal);
+
+ si = h->siginfo;
+ while (h->nr_pending--) {
+ q = sigqueue_alloc();
+ if (!q) {
+ ret = -ENOMEM;
+ break;
+ }
+
+ ret = load_siginfo(&q->info, si++);
+ if (ret < 0) {
+ sigqueue_free(q);
+ break;
+ }
+
+ q->flags &= ~SIGQUEUE_PREALLOC;
+ list_add_tail(&pending->list, &q->list);
+ }
+
+ if (ret < 0)
+ flush_sigqueue(pending);
+ out:
+ ckpt_hdr_put(ctx, h);
+ return ret;
+}
+
static int restore_signal(struct ckpt_ctx *ctx)
{
struct ckpt_hdr_signal *h;
+ struct sigpending new_pending;
+ struct sigpending *pending;
struct rlimit rlim;
int i, ret;

@@ -2958,8 +3181,20 @@ static int restore_signal(struct ckpt_ctx *ctx)
rlim.rlim_max = h->rlim[i].rlim_max;
ret = do_setrlimit(i, &rlim);
if (ret < 0)
- break;
+ goto out;
}
+
+ ret = restore_sigpending(ctx, &new_pending);
+ if (ret < 0)
+ goto out;
+
+ spin_lock_irq(&current->sighand->siglock);
+ pending = &current->signal->shared_pending;
+ flush_sigqueue(pending);
+ pending->signal = new_pending.signal;
+ list_splice_init(&new_pending.list, &pending->list);
+ spin_unlock_irq(&current->sighand->siglock);
+out:
ckpt_hdr_put(ctx, h);
return ret;
}
@@ -2969,7 +3204,7 @@ int restore_obj_signal(struct ckpt_ctx *ctx, int signal_objref)
struct signal_struct *signal;
int ret = 0;

- signal = ckpt_obj_fetch(ctx, signal_objref, CKPT_OBJ_SIGNAL);
+ signal = ckpt_obj_try_fetch(ctx, signal_objref, CKPT_OBJ_SIGNAL);
if (!IS_ERR(signal)) {
/*
* signal_struct is already shared properly as it is
@@ -2994,8 +3229,34 @@ int restore_obj_signal(struct ckpt_ctx *ctx, int signal_objref)
int checkpoint_task_signal(struct ckpt_ctx *ctx, struct task_struct *t)
{
struct ckpt_hdr_signal_task *h;
+ struct sigpending pending;
+ unsigned long flags;
int ret;

+ INIT_LIST_HEAD(&pending.list);
+
+ /* temporarily borrow signal queue - see chekcpoint_sigpending() */
+ if (!lock_task_sighand(t, &flags)) {
+ ckpt_err(ctx, -EBUSY, "%(T)signand missing\n");
+ return -EBUSY;
+ }
+ list_splice_init(&t->pending.list, &pending.list);
+ pending.signal = t->pending.signal;
+ unlock_task_sighand(t, &flags);
+
+ ret = checkpoint_sigpending(ctx, &pending);
+
+ /* re-attach the borrowed queue */
+ if (!lock_task_sighand(t, &flags)) {
+ ckpt_err(ctx, -EBUSY, "%(T)signand missing\n");
+ return -EBUSY;
+ }
+ list_splice(&pending.list, &t->pending.list);
+ unlock_task_sighand(t, &flags);
+
+ if (ret < 0)
+ return ret;
+
h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_SIGNAL_TASK);
if (!h)
return -ENOMEM;
@@ -3013,7 +3274,21 @@ int checkpoint_task_signal(struct ckpt_ctx *ctx, struct task_struct *t)
int restore_task_signal(struct ckpt_ctx *ctx)
{
struct ckpt_hdr_signal_task *h;
+ struct sigpending new_pending;
+ struct sigpending *pending;
sigset_t blocked;
+ int ret;
+
+ ret = restore_sigpending(ctx, &new_pending);
+ if (ret < 0)
+ return ret;
+
+ spin_lock_irq(&current->sighand->siglock);
+ pending = &current->pending;
+ flush_sigqueue(pending);
+ pending->signal = new_pending.signal;
+ list_splice_init(&new_pending.list, &pending->list);
+ spin_unlock_irq(&current->sighand->siglock);

h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_SIGNAL_TASK);
if (IS_ERR(h))
--
1.6.3.3


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