Date: Fri, 04 May 2007 15:57:26 -0600 From: Scott Long <scottl@samsco.org> To: Julian Elischer <julian@elischer.org> Cc: attilio@freebsd.org, freebsd-current@freebsd.org, Harald Schmalzbauer <h.schmalzbauer@omnisec.de> Subject: Re: PANIC: blockable slep lock (sx) msi @ ....msi.c:374 Message-ID: <463BAC46.9030200@samsco.org> In-Reply-To: <463BA850.8000804@elischer.org> References: <463B7A1D.6020602@omnisec.de> <463BF1A7.1050504@FreeBSD.org> <200705041546.50690.jhb@freebsd.org> <463BA850.8000804@elischer.org>
next in thread | previous in thread | raw e-mail | index | archive | help
Julian Elischer wrote: > John Baldwin wrote: > >> >> This is wrong because once you do critical_enter(), you are free to >> assume that you won't do a context switch until you critical_exit(), >> and sx_xlock() would violate that if it blocked on the lock. > > wellllll critical enter doesn't block interupts so it's true if you > don't call > an interrupt as a context switch. > (it doesn't SWITCH contexts but it does step into a different context.) > Yes, interrupts are serviced when a critical section is entered, but ithreads are not run on the same CPU until the critical section is exited. This has been debated quite a bit over the last few years, but I it's a good compromise. This implications just don't seem to be documented well, especially for those who need a protected, uninterruptable context for doing time-critical operations. Scott
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?463BAC46.9030200>