The patch titled
Subject: coredump: ensure that SIGKILL always kills the dumping thread
has been added to the -mm tree. Its filename is
coredump-ensure-that-sigkill-always-kills-the-dumping-thread.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Oleg Nesterov <oleg@xxxxxxxxxx>
Subject: coredump: ensure that SIGKILL always kills the dumping thread
prepare_signal() blesses SIGKILL sent to the dumping process but this
signal can be "lost" anyway. The problems is, complete_signal() sees
SIGNAL_GROUP_EXIT and skips the "kill them all" logic. And even if the
dumping process is single-threaded (so the target is always "correct"),
the group-wide SIGKILL is not recorded in task->pending and thus
__fatal_signal_pending() won't be true. A multi-threaded case has even
more problems.
And even ignoring all technical details, SIGNAL_GROUP_EXIT doesn't look
right to me. This coredumping process is not exiting yet, it can do a lot
of work dumping the core.
With this patch the dumping process doesn't have SIGNAL_GROUP_EXIT, we set
signal->group_exit_task instead. This makes signal_group_exit() true and
thus this should equally close the races with exit/exec/stop but allows to
kill the dumping thread reliably.
Notes:
- It is not clear what should we do with ->group_exit_code
if the dumper was killed, see the next change.
- we need more (hopefully straightforward) changes to ensure
that SIGKILL actually interrupts the coredump. Basically we
need to check __fatal_signal_pending() in dump_write() and
dump_seek().
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Tested-by: Mandeep Singh Baines <msb@xxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Neil Horman <nhorman@xxxxxxxxxx>
Cc: "Rafael J. Wysocki" <rjw@xxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/coredump.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff -puN fs/coredump.c~coredump-ensure-that-sigkill-always-kills-the-dumping-thread fs/coredump.c
--- a/fs/coredump.c~coredump-ensure-that-sigkill-always-kills-the-dumping-thread
+++ a/fs/coredump.c
@@ -263,7 +263,6 @@ static int zap_process(struct task_struc
struct task_struct *t;
int nr = 0;
- start->signal->flags = SIGNAL_GROUP_EXIT;
start->signal->group_exit_code = exit_code;
start->signal->group_stop_count = 0;
@@ -291,8 +290,9 @@ static int zap_threads(struct task_struc
if (!signal_group_exit(tsk->signal)) {
mm->core_state = core_state;
nr = zap_process(tsk, exit_code);
+ tsk->signal->group_exit_task = tsk;
/* ignore all signals except SIGKILL, see prepare_signal() */
- tsk->signal->flags |= SIGNAL_GROUP_COREDUMP;
+ tsk->signal->flags = SIGNAL_GROUP_COREDUMP;
clear_tsk_thread_flag(tsk, TIF_SIGPENDING);
}
spin_unlock_irq(&tsk->sighand->siglock);
@@ -343,6 +343,7 @@ static int zap_threads(struct task_struc
if (unlikely(p->mm == mm)) {
lock_task_sighand(p, &flags);
nr += zap_process(p, exit_code);
+ p->signal->flags = SIGNAL_GROUP_EXIT;
unlock_task_sighand(p, &flags);
}
break;
@@ -394,6 +395,11 @@ static void coredump_finish(struct mm_st
struct core_thread *curr, *next;
struct task_struct *task;
+ spin_lock_irq(¤t->sighand->siglock);
+ current->signal->group_exit_task = NULL;
+ current->signal->flags = SIGNAL_GROUP_EXIT;
+ spin_unlock_irq(¤t->sighand->siglock);
+
next = mm->core_state->dumper.next;
while ((curr = next) != NULL) {
next = curr->next;
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
origin.patch
linux-next.patch
signal-allow-to-send-any-siginfo-to-itself.patch
kernel-signalc-fix-suboptimal-printk-usage.patch
coredump-only-sigkill-should-interrupt-the-coredumping-task.patch
coredump-ensure-that-sigkill-always-kills-the-dumping-thread.patch
coredump-sanitize-the-setting-of-signal-group_exit_code.patch
vfork-dont-freezer_count-for-in-kernel-users-of-clone_vfork.patch
lockdep-check-that-no-locks-held-at-freeze-time.patch
lockdep-check-that-no-locks-held-at-freeze-time-fix.patch
coredump-cleanup-the-waiting-for-coredump_finish-code.patch
coredump-use-a-freezable_schedule-for-the-coredump_finish-wait.patch
coredump-abort-core-dump-piping-only-due-to-a-fatal-signal.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
