Date: Sat, 19 Jun 1999 15:50:01 -0700 (PDT) From: Bruce Evans <bde@zeta.org.au> To: freebsd-bugs@FreeBSD.org Subject: Re: kern/12247: userlevel program let kernel hang Message-ID: <199906192250.PAA24663@freefall.freebsd.org>
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The following reply was made to PR kern/12247; it has been noted by GNATS. From: Bruce Evans <bde@zeta.org.au> To: bde@zeta.org.au, tejblum@arc.hq.cti.ru Cc: freebsd-gnats-submit@FreeBSD.ORG Subject: Re: kern/12247: userlevel program let kernel hang Date: Sun, 20 Jun 1999 08:45:53 +1000 >> tsleep()'s return codes are poorly documented and were >> misinterpreted in lf_setlock(). tsleep() can return 0 if the process >> was restarted by a debugger, > >I didn't realise that a process sleeping interruptible can be stopped >inside the tsleep call (is that true?). It looks dangerous to me. For I think it isn't true. >example, interruptible nfs may sleep interuuptible, in particular in >the vfs_bio code, with vnode locks held, etc. Stopping at such point >looks like a good opportunity to hang the machine... PT_ATTACH is implemented using SIGSTOP, but the consequences shouldn't be any worse than for a manual kill -STOP. I think SIGSTOP of a stopped process is normally optimised away (so tsleep() doesn't return), but for ptrace() it is explicitly pessimised (so tsleep() returns 0). Bruce To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-bugs" in the body of the message
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