Re: [PATCH] powerpc: Fix race in the pasemi timebase calibration
From: Paul Mackerras <hidden>
Date: 2007-08-22 01:27:33
Olof Johansson writes:
Make sure the new timebase value is available by the time take_timebase completes. Otherwise take_timebase might race with give_timebase, causing severe badness when the value later is modified (think looong hang trying to catch up with a very large number of lost ticks).
OK.
quoted hunk ↗ jump to hunk
@@ -61,6 +62,7 @@ static void __devinit pas_give_timebase( mtspr(SPRN_TBCTL, TBCTL_UPDATE_LOWER | (tb & 0xffffffff)); mtspr(SPRN_TBCTL, TBCTL_UPDATE_UPPER | (tb >> 32)); mtspr(SPRN_TBCTL, TBCTL_RESTART); + timebase_avail = 1;
No memory barrier before setting timebase_avail? Shouldn't there be one? Actually I don't understand that code at all. Your give_timebase seems to freeze the timebase, read it, set it to the same value and restart, all without synchronizing with the other cpu, and your take_timebase does nothing except print the timebase. How does that work? Regards, Paul.