Re: [PATCH man-pages v2] madvise.2: add MADV_GUARD_INSTALL, MADV_GUARD_REMOVE description

[Jann Horn <jannh@google.com>]

On Fri, Nov 29, 2024 at 4:59 PM Lorenzo Stoakes
<lorenzo.stoakes@oracle.com> wrote:
> Lightweight guard region support has been added to Linux 6.13, which adds
> MADV_GUARD_INSTALL and MADV_GUARD_REMOVE flags to the madvise() system
> call. Therefore, update the manpage for madvise() and describe these
> operations.
[...]
> +.TP
> +.BR MADV_GUARD_INSTALL " (since Linux 6.13)"
> +Install a lightweight guard region into the range specified by
> +.I addr
> +and
> +.IR size ,
> +causing any read or write in the range to result in a fatal
> +.B SIGSEGV
> +signal being raised.

Single-word nitpick: Maybe remove the word "fatal"?

I think the term "fatal signal" normally refers to a signal that is
guaranteed to terminate the task (that's how the signal handling code
uses the term, more or less); but a SIGSEGV caused by VM_FAULT_SIGSEGV
can AFAIK be handled by a userspace signal handler.

SIGKILL is the one signal that is always fatal; the kernel can also
send other signals in an always-fatal way, like with force_fatal_sig()
or force_exit_sig(), but those are not used for VM_FAULT_SIGSEGV.
(Those functions are mostly for cases where we can't continue because
something is in an unsafe state, like if a signal return failed and
the register state might now be messed up.)