+ simplify-force_sig_info_to_task-kill-recalc_sigpending_and_wake.patch added to mm-nonmm-unstable branch

+ simplify-force_sig_info_to_task-kill-recalc_sigpending_and_wake.patch added to mm-nonmm-unstable branch

[Andrew Morton]

The patch titled
     Subject: kernel/signal.c: simplify force_sig_info_to_task(), kill recalc_sigpending_and_wake()
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     simplify-force_sig_info_to_task-kill-recalc_sigpending_and_wake.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/simplify-force_sig_info_to_task-kill-recalc_sigpending_and_wake.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Oleg Nesterov <oleg@redhat.com>
Subject: kernel/signal.c: simplify force_sig_info_to_task(), kill recalc_sigpending_and_wake()
Date: Mon, 20 Nov 2023 16:16:49 +0100

The purpose of recalc_sigpending_and_wake() is not clear, it looks
"obviously unneeded" because we are going to send the signal which can't
be blocked or ignored.

Add the comment to explain why we can't rely on send_signal_locked() and
make this logic more simple/explicit.  recalc_sigpending_and_wake() has no
other users, it can die.

In fact I think we don't even need signal_wake_up(), the target task must
be either current or a TASK_TRACED child, otherwise the usage of siglock
is not safe.  But this needs another change.

Link: https://lkml.kernel.org/r/20231120151649.GA15995@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/sched/signal.h |    1 -
 kernel/signal.c              |   17 ++++-------------
 2 files changed, 4 insertions(+), 14 deletions(-)

--- a/include/linux/sched/signal.h~simplify-force_sig_info_to_task-kill-recalc_sigpending_and_wake
+++ a/include/linux/sched/signal.h
@@ -432,7 +432,6 @@ static inline bool fault_signal_pending(
  * This is required every time the blocked sigset_t changes.
  * callers must hold sighand->siglock.
  */
-extern void recalc_sigpending_and_wake(struct task_struct *t);
 extern void recalc_sigpending(void);
 extern void calculate_sigpending(void);
 
--- a/kernel/signal.c~simplify-force_sig_info_to_task-kill-recalc_sigpending_and_wake
+++ a/kernel/signal.c
@@ -171,16 +171,6 @@ static bool recalc_sigpending_tsk(struct
 	return false;
 }
 
-/*
- * After recalculating TIF_SIGPENDING, we need to make sure the task wakes up.
- * This is superfluous when called on current, the wakeup is a harmless no-op.
- */
-void recalc_sigpending_and_wake(struct task_struct *t)
-{
-	if (recalc_sigpending_tsk(t))
-		signal_wake_up(t, 0);
-}
-
 void recalc_sigpending(void)
 {
 	if (!recalc_sigpending_tsk(current) && !freezing(current))
@@ -1348,10 +1338,8 @@ force_sig_info_to_task(struct kernel_sig
 		action->sa.sa_handler = SIG_DFL;
 		if (handler == HANDLER_EXIT)
 			action->sa.sa_flags |= SA_IMMUTABLE;
-		if (blocked) {
+		if (blocked)
 			sigdelset(&t->blocked, sig);
-			recalc_sigpending_and_wake(t);
-		}
 	}
 	/*
 	 * Don't clear SIGNAL_UNKILLABLE for traced tasks, users won't expect
@@ -1361,6 +1349,9 @@ force_sig_info_to_task(struct kernel_sig
 	    (!t->ptrace || (handler == HANDLER_EXIT)))
 		t->signal->flags &= ~SIGNAL_UNKILLABLE;
 	ret = send_signal_locked(sig, info, t, PIDTYPE_PID);
+	/* This can happen if the signal was already pending and blocked */
+	if (!task_sigpending(t))
+		signal_wake_up(t, 0);
 	spin_unlock_irqrestore(&t->sighand->siglock, flags);
 
 	return ret;
_

Patches currently in -mm which might be from oleg@redhat.com are

introduce-for_other_threadsp-t.patch
simplify-force_sig_info_to_task-kill-recalc_sigpending_and_wake.patch