In a checkpoint of a child namespace, it is possible that sid or pgid
will be 0 (meaning, they are from a process outside that namespace).
Restarting from such an image with --pidns is easy, and works well.
However, restarting with --no-pids didn't work because we can't deal
with zero pids.
This patch fixes the problem for subtree restart (--no-pidns). If it
finds sid/pgid that are zero, it creates a special ghost task, and
substitutes its pid for all those 0's.
(Also get rid of un-suqashing of sid/pgid == 0 in ckpt_adjust_pids()
because there should no longer be any 0's there).
Signed-off-by: Oren Laadan <orenl@xxxxxxxxxxxxxxx>
---
restart.c | 127 +++++++++++++++++++++++++++++++++++++------------------------
1 files changed, 77 insertions(+), 50 deletions(-)
diff --git a/restart.c b/restart.c
index 2efe879..0c438c2 100644
--- a/restart.c
+++ b/restart.c
@@ -250,9 +250,6 @@ struct task zero_task;
#define TASK_NEWPID 0x20 /* starts a new pid namespace */
#define TASK_DEAD 0x40 /* dead task (dummy) */
-#define TASK_ZERO_SID 0x100 /* sid was temporarily zeroed */
-#define TASK_ZERO_PGID 0x200 /* pgid was temporarily zeroed */
-
struct ckpt_ctx {
pid_t root_pid;
int pipe_in;
@@ -1239,6 +1236,41 @@ static int ckpt_valid_pid(struct ckpt_ctx *ctx, pid_t pid, char *which, int i)
return 1;
}
+static int ckpt_alloc_pid(struct ckpt_ctx *ctx)
+{
+ int n = 0;
+
+ /*
+ * allocate an unused pid for the placeholder
+ * (this will become inefficient if pid-space is exhausted)
+ */
+ do {
+ if (ctx->tasks_pid == INT_MAX)
+ ctx->tasks_pid = 2;
+ else
+ ctx->tasks_pid++;
+
+ if (n++ == INT_MAX) { /* ohhh... */
+ ckpt_err("pid namsepace exhausted");
+ return -1;
+ }
+ } while (hash_lookup(ctx, ctx->tasks_pid));
+
+ return ctx->tasks_pid;
+}
+
+static int ckpt_zero_pid(struct ckpt_ctx *ctx)
+{
+ pid_t pid;
+
+ pid = ckpt_alloc_pid(ctx);
+ if (pid < 0)
+ return -1;
+ if (ckpt_setup_task(ctx, pid, ctx->pids_arr[0].vpid) < 0)
+ return -1;
+ return pid;
+}
+
static int ckpt_init_tree(struct ckpt_ctx *ctx)
{
struct ckpt_pids *pids_arr = ctx->pids_arr;
@@ -1246,6 +1278,7 @@ static int ckpt_init_tree(struct ckpt_ctx *ctx)
struct task *task;
pid_t root_pid;
pid_t root_sid;
+ pid_t zero_pid = 0;
int i;
root_pid = pids_arr[0].vpid;
@@ -1257,16 +1290,20 @@ static int ckpt_init_tree(struct ckpt_ctx *ctx)
* same as root_pid or 0), and root_sid was inherited from an
* ancestor of that subtree.
*
- * So we make the root-task also inherit sid from its ancestor
- * (== coordinator), whatever 'restart' task currently has.
- * For that, we force the root-task's sid and all references
- * to it from other tasks (via sid and pgid), to 0. Later, the
- * feeder will substitute the cooridnator's sid for them.
+ * If we restart with --pidns, make the root-task also inherit
+ * sid from its ancestor (== coordinator), whatever 'restart'
+ * task currently has. For that, we force the root-task's sid
+ * and all references to it from other tasks (via sid and
+ * pgid), to 0. Later, the feeder will substitute the
+ * cooridnator's sid for them.
*
* (Note that this still works even if the coordinator's sid
* is "used" by a restarting task: a new-pidns restart will
* fail because the pid is in use, and in an old-pidns restart
* the task will be assigned a new pid anyway).
+ *
+ * If we restart with --no-pidns, we'll add a ghost task below
+ * whose pid will be used instead of these zeroed entried.
*/
/* forcing root_sid to -1, will make comparisons below fail */
@@ -1288,15 +1325,10 @@ static int ckpt_init_tree(struct ckpt_ctx *ctx)
else if (!ckpt_valid_pid(ctx, pids_arr[i].vpgid, "pgid", i))
return -1;
- /* zero references to root_sid (root_sid != root_pid) */
- if (pids_arr[i].vsid == root_sid) {
- task->flags |= TASK_ZERO_SID;
+ if (pids_arr[i].vsid == root_sid)
pids_arr[i].vsid = 0;
- }
- if (pids_arr[i].vpgid == root_sid) {
- task->flags |= TASK_ZERO_PGID;
+ if (pids_arr[i].vpgid == root_sid)
pids_arr[i].vpgid = 0;
- }
task->pid = pids_arr[i].vpid;
task->ppid = pids_arr[i].vppid;
@@ -1324,6 +1356,9 @@ static int ckpt_init_tree(struct ckpt_ctx *ctx)
sid = pids_arr[i].vsid;
+ /* Remember if we find any vsid/vpgid - see below */
+ if (pids_arr[i].vsid == 0 || pids_arr[i].vpgid == 0)
+ zero_pid = 1;
/*
* An unaccounted-for sid belongs to a task that was a
* session leader and died. We can safe set its parent
@@ -1360,6 +1395,27 @@ static int ckpt_init_tree(struct ckpt_ctx *ctx)
return -1;
}
+ /*
+ * Zero sid/pgid is disallowed in --no-pidns mode. If there
+ * were any, we invent a new ghost-zero task and substitute
+ * its pid for those any sid/pgid.
+ */
+ if (zero_pid && !ctx->args->pidns) {
+ zero_pid = ckpt_zero_pid(ctx);
+ if (zero_pid < 0)
+ return -1;
+ for (i = 0; i < pids_nr; i++) {
+ if (pids_arr[i].vsid == 0) {
+ pids_arr[i].vsid = zero_pid;
+ pids_arr[i].vppid = zero_pid;
+ }
+ if (pids_arr[i].vpgid == 0) {
+ pids_arr[i].vpgid = zero_pid;
+ pids_arr[i].vppid = zero_pid;
+ }
+ }
+ }
+
/* mark root task(s), and set its "creator" to be zero_task */
ckpt_init_task(ctx)->flags |= TASK_ROOT;
ckpt_init_task(ctx)->creator = &zero_task;
@@ -1534,7 +1590,7 @@ static int ckpt_placeholder_task(struct ckpt_ctx *ctx, struct task *task)
{
struct task *session = hash_lookup(ctx, task->sid);
struct task *holder = &ctx->tasks_arr[ctx->tasks_nr++];
- int n = 0;
+ pid_t pid;
if (ctx->tasks_nr > ctx->tasks_max) {
/* shouldn't happen, beacuse we prepared enough */
@@ -1542,27 +1598,15 @@ static int ckpt_placeholder_task(struct ckpt_ctx *ctx, struct task *task)
return -1;
}
- /*
- * allocate an unused pid for the placeholder
- * (this will become inefficient if pid-space is exhausted)
- */
- do {
- if (ctx->tasks_pid == INT_MAX)
- ctx->tasks_pid = 2;
- else
- ctx->tasks_pid++;
-
- if (n++ == INT_MAX) { /* ohhh... */
- ckpt_err("pid namsepace exhausted");
- return -1;
- }
- } while (hash_lookup(ctx, ctx->tasks_pid));
+ pid = ckpt_alloc_pid(ctx);
+ if (pid < 0)
+ return -1;
holder->flags = TASK_DEAD;
- holder->pid = ctx->tasks_pid;
+ holder->pid = pid;
holder->ppid = ckpt_init_task(ctx)->pid;
- holder->tgid = holder->pid;
+ holder->tgid = pid;
holder->sid = task->sid;
holder->children = NULL;
@@ -2097,23 +2141,6 @@ static int ckpt_adjust_pids(struct ckpt_ctx *ctx)
}
}
- if (!ctx->args->pidns) {
- /*
- * If a task's {sid,pgid} was zeroed out (in ckpt_init_tree)
- * then substitute the coordinator's sid for it now. (This
- * should leave no more 0's in restart of subtree-checkpoint).
- *
- * NOTE: thanks to the construction of tasks_arr[], the first
- * ctx->pid_nr entries in both arrays match (the same pids).
- */
- for (m = 0; m < ctx->pids_nr; m++) {
- if (ctx->tasks_arr[m].flags & TASK_ZERO_SID)
- ctx->copy_arr[m].vsid = coord_sid;
- if (ctx->tasks_arr[m].flags & TASK_ZERO_PGID)
- ctx->copy_arr[m].vpgid = coord_sid;
- }
- }
-
memcpy(ctx->pids_arr, ctx->copy_arr, len);
#ifdef CHECKPOINT_DEBUG
--
1.6.0.4
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