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authorLinus Torvalds <torvalds@linux-foundation.org>2020-01-03 11:17:14 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2020-01-03 11:17:14 -0800
commitd9c82fd8c89766f2cf1e667f663e8e8c25c12aee (patch)
tree57d416495f7a1c178d4105e2946dad78014300af /kernel
parent6f2e9c3d28167b0f27d4be68e9101a9ecf397878 (diff)
parent43cf75d96409a20ef06b756877a2e72b10a026fc (diff)
Merge tag 'for-linus-2020-01-03' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux
Pull thread fixes from Christian Brauner: "Here are two fixes: - Panic earlier when global init exits to generate useable coredumps. Currently, when global init and all threads in its thread-group have exited we panic via: do_exit() -> exit_notify() -> forget_original_parent() -> find_child_reaper() This makes it hard to extract a useable coredump for global init from a kernel crashdump because by the time we panic exit_mm() will have already released global init's mm. We now panic slightly earlier. This has been a problem in certain environments such as Android. - Fix a race in assigning and reading taskstats for thread-groups with more than one thread. This patch has been waiting for quite a while since people disagreed on what the correct fix was at first" * tag 'for-linus-2020-01-03' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux: exit: panic before exit_mm() on global init exit taskstats: fix data-race
Diffstat (limited to 'kernel')
-rw-r--r--kernel/exit.c12
-rw-r--r--kernel/taskstats.c30
2 files changed, 27 insertions, 15 deletions
diff --git a/kernel/exit.c b/kernel/exit.c
index bcbd59888e67..2833ffb0c211 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -517,10 +517,6 @@ static struct task_struct *find_child_reaper(struct task_struct *father,
}
write_unlock_irq(&tasklist_lock);
- if (unlikely(pid_ns == &init_pid_ns)) {
- panic("Attempted to kill init! exitcode=0x%08x\n",
- father->signal->group_exit_code ?: father->exit_code);
- }
list_for_each_entry_safe(p, n, dead, ptrace_entry) {
list_del_init(&p->ptrace_entry);
@@ -766,6 +762,14 @@ void __noreturn do_exit(long code)
acct_update_integrals(tsk);
group_dead = atomic_dec_and_test(&tsk->signal->live);
if (group_dead) {
+ /*
+ * If the last thread of global init has exited, panic
+ * immediately to get a useable coredump.
+ */
+ if (unlikely(is_global_init(tsk)))
+ panic("Attempted to kill init! exitcode=0x%08x\n",
+ tsk->signal->group_exit_code ?: (int)code);
+
#ifdef CONFIG_POSIX_TIMERS
hrtimer_cancel(&tsk->signal->real_timer);
exit_itimers(tsk->signal);
diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index 13a0f2e6ebc2..e2ac0e37c4ae 100644
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -554,25 +554,33 @@ static int taskstats_user_cmd(struct sk_buff *skb, struct genl_info *info)
static struct taskstats *taskstats_tgid_alloc(struct task_struct *tsk)
{
struct signal_struct *sig = tsk->signal;
- struct taskstats *stats;
+ struct taskstats *stats_new, *stats;
- if (sig->stats || thread_group_empty(tsk))
- goto ret;
+ /* Pairs with smp_store_release() below. */
+ stats = smp_load_acquire(&sig->stats);
+ if (stats || thread_group_empty(tsk))
+ return stats;
/* No problem if kmem_cache_zalloc() fails */
- stats = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL);
+ stats_new = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL);
spin_lock_irq(&tsk->sighand->siglock);
- if (!sig->stats) {
- sig->stats = stats;
- stats = NULL;
+ stats = sig->stats;
+ if (!stats) {
+ /*
+ * Pairs with smp_store_release() above and order the
+ * kmem_cache_zalloc().
+ */
+ smp_store_release(&sig->stats, stats_new);
+ stats = stats_new;
+ stats_new = NULL;
}
spin_unlock_irq(&tsk->sighand->siglock);
- if (stats)
- kmem_cache_free(taskstats_cache, stats);
-ret:
- return sig->stats;
+ if (stats_new)
+ kmem_cache_free(taskstats_cache, stats_new);
+
+ return stats;
}
/* Send pid data out on exit */

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