Merge patch series "fix reading ESP during coredump"

Nam Cao <namcao@linutronix.de> says:

In /proc/PID/stat, there is the kstkesp field which is the stack pointer of
a thread. While the thread is active, this field reads zero. But during a
coredump, it should have a valid value.

However, at the moment, kstkesp is zero even during coredump.

The first commit fixes this problem, and the second commit adds a selftest
to detect if this problem appears again in the future.

* patches from https://lore.kernel.org/r/cover.1735805772.git.namcao@linutronix.de:
  selftests: coredump: Add stackdump test
  fs/proc: do_task_stat: Fix ESP not readable during coredump

Link: https://lore.kernel.org/r/cover.1735805772.git.namcao@linutronix.de
Signed-off-by: Christian Brauner <brauner@kernel.org>