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Li RongQing 9544f9e694 hung_task: panic when there are more than N hung tasks at the same time

The hung_task_panic sysctl is currently a blunt instrument: it's all or
nothing.

Panicking on a single hung task can be an overreaction to a transient
glitch.  A more reliable indicator of a systemic problem is when
multiple tasks hang simultaneously.

Extend hung_task_panic to accept an integer threshold, allowing the
kernel to panic only when N hung tasks are detected in a single scan. 
This provides finer control to distinguish between isolated incidents
and system-wide failures.

The accepted values are:
- 0: Don't panic (unchanged)
- 1: Panic on the first hung task (unchanged)
- N > 1: Panic after N hung tasks are detected in a single scan

The original behavior is preserved for values 0 and 1, maintaining full
backward compatibility.

[lance.yang@linux.dev: new changelog]
Link: https://lkml.kernel.org/r/20251015063615.2632-1-lirongqing@baidu.com
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Tested-by: Lance Yang <lance.yang@linux.dev>
Acked-by: Andrew Jeffery <andrew@codeconstruct.com.au> [aspeed_g5_defconfig]
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: Florian Wesphal <fw@strlen.de>
Cc: Jakub Kacinski <kuba@kernel.org>
Cc: Jason A. Donenfeld <jason@zx2c4.com>
Cc: Joel Granados <joel.granados@kernel.org>
Cc: Joel Stanley <joel@jms.id.au>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kees Cook <kees@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Phil Auld <pauld@redhat.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Simon Horman <horms@kernel.org>
Cc: Stanislav Fomichev <sdf@fomichev.me>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>