linux-kernel - Re: Any lightweight way for one thread to force another thread to suspend execution?

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] [day] [month] [year] [list]

Date:	Tue, 24 Jun 2008 09:59:24 +0200
From:	Mikael Pettersson <mikpe@...uu.se>
To:	"Eric Smith" <eric@...uhaha.com>
Cc:	"Andi Kleen" <andi@...stfloor.org>, linux-kernel@...r.kernel.org
Subject: Re: Any lightweight way for one thread to force another thread to  
     suspend execution?

Eric Smith writes:
 > Andi wrote about my inquire regarding a way to synchronously stop
 > another thread:
 > > Any such mechanism will need a syscall, and it's unlikely that
 > > any syscall will get much cheaper than a kill(SIGSTOP)
 > 
 > Unfortunately, as Bart pointed out, this stops ALL the threads
 > in a process (required for POSIX conformance).  However, it appears that
 > I may be able to do it by creating my threads using clone() with appropriate
 > parameters rather than pthread_create().
 > 
 > The next question, which I haven't yet been able to answer for myself
 > from staring at the kernel sources, is whether sending SIGSTOP is
 > synchronous.  In other words, when the kill() returns, is the target
 > thread already stopped?  Even on an SMP system where the thread may have
 > been executing concurrently on another processor?
 > 
 > If not, the next question will be whether there's a more efficient way
 > to wait for a process to enter the "T" state than busy-polling a file
 > in /proc.

SIGSTOP is unreliable since some other process may wake the
target up with a SIGCONT.

man ptrace(), see the PTRACE_ATTACH request.

(Presumably it will DTRT if you give it a tid not just a pid,
but I haven't tested that.)
--
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/