Date: Tue, 30 Sep 2003 21:37:33 -0700 (PDT) From: Warner Losh <imp@FreeBSD.org> To: Perforce Change Reviews <perforce@freebsd.org> Subject: PERFORCE change 38947 for review Message-ID: <200310010437.h914bXI4059942@repoman.freebsd.org>
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http://perforce.freebsd.org/chv.cgi?CH=38947 Change 38947 by imp@imp_koguchi on 2003/09/30 21:36:37 document the race in the callout api. this one sucks since if we lose this one we can have a crash. Affected files ... .. //depot/doc/strawman-driver.c#8 edit Differences ... ==== //depot/doc/strawman-driver.c#8 (text+ko) ==== @@ -83,7 +83,7 @@ /* Everybody active here */ if (callout_stop(&sc->stat_ch, hz, fxp_tick, sc) == 0) - printf("Maybe we just lost a race\n"); + printf("Maybe we just lost a race\n"); /* race 3 */ /* Network, ISR and devsw active */ bus_teardown_intr(sc->dev, sc->irq, sc->ih); @@ -116,8 +116,6 @@ /* #1 * - * We have a race here. - * * The test points 'a' and 'b' might lose the race with the set point 'c'. * * If 'c' wins the race with either 'a' or 'b', then we're OK. We properly @@ -137,3 +135,13 @@ * before 'a', that's OK, because sc is guaranteed to be valid for the * life of the call to ioctl, or any of the devsw functions. */ + +/* #3 + * + * Callout interface is inharently racy. We have no way of knowing + * when a callout might be in progress or complete. A return value of + * 0 means either the callout has happened, or is happening. However, + * we can't tell if the code has finished executing or not. This + * means that if the code is executing and we try to unload the page + * that is executing, then we've set ourselves up for a crash. + */
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