linux-kernel - Re: [PATCH 2/4] set_restore_sigmask TIF

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.LFD.1.00.0803281746480.14670@woody.linux-foundation.org>
Date:	Fri, 28 Mar 2008 17:53:16 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Roland McGrath <roland@...hat.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-s390@...r.kernel.org, tony.luck@...el.com,
	linux-ia64@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] set_restore_sigmask TIF_SIGPENDING

On Fri, 28 Mar 2008, Roland McGrath wrote:
>
> Set TIF_SIGPENDING in set_restore_sigmask.  This lets arch code take
> TIF_RESTORE_SIGMASK out of the set of bits that will be noticed on
> return to user mode.  On some machines those bits are scarce, and we
> can free this unneeded one up for other uses.

Hmm. That probably means that TIF_RESTORE_SIGMASK shouldn't be a "TIF" 
flag at all, but a "TS" ("thread status") flag.

The TS flags are faster, because they are thread-synchronous and do not 
need atomic accesses (ie they are purely thread-local in setting, testing 
and clearing).

Of course, it may well not be worth it. Unlike the TIF flags, the TS flags 
have been architecture-specific and I don't think all architectures even 
do them (x86 uses them for FP state bits and stuff like that).

I guess TIF_RESTORE_SIGMASK is never *so* performance-critical that we'd 
care about the difference between a single cycle (approx) for a non-atomic 
"or" into memory and an atomic bitop (~50 cycles or so). 

			Linus
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/