On Thu, Apr 30, 2020 at 08:53:56AM +0200, Jiri Slaby wrote:

On 30. 04. 20, 8:42, Arseny Maslennikov wrote:

quoted

This matches the behaviour of other Unix-like systems that have SIGINFO
and causes less harm to processes that do not install handlers for this
signal, making the keyboard status character non-fatal for them.

This is implemented with the assumption that SIGINFO is defined
to be equivalent to SIGPWR; still, there is no reason for PWR to
result in termination of the signal recipient anyway — it does not
indicate there is a fatal problem with the recipient's execution
context (like e.g. FPE/ILL do), and we have TERM/KILL for explicit
termination requests.

To put it another way:
The only scenario where system behaviour actually changes is when the
signal recipient has default disposition for SIGPWR. If a process
chose to interpret a SIGPWR as an incentive to cleanly terminate, it
would supply its own handler — and this commit does not affect processes
with non-default handlers.

Signed-off-by: Arseny Maslennikov <redacted>
---
 include/linux/signal.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/signal.h b/include/linux/signal.h
index 05bacd2ab..dc31da8fc 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h

@@ -369,7 +369,7 @@ extern bool unhandled_signal(struct task_struct *tsk, int sig);
  *	|  SIGSYS/SIGUNUSED  |	coredump 	|
  *	|  SIGSTKFLT         |	terminate	|
  *	|  SIGWINCH          |	ignore   	|
- *	|  SIGPWR            |	terminate	|
+ *	|  SIGPWR            |	ignore   	|

You need to update signal.7 too:
https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/man7/signal.7#n285

(I fail this whole thread via b4 and it appears that a bunch of messages
are missing on lore. Might just be delay though.)

How this is this not going to break userspace?
Just for a start, SIGPWR (for better or worse) was used for a long time
by some sandboxing/container runtimes to shutdown a process and still
is.

Christian