On Wed, Aug 17, 2016 at 08:31:20PM +0100, Al Viro wrote: > On Wed, Aug 17, 2016 at 03:24:38PM -0400, Rob Clark wrote: > > > hmm, looks like, at least on arm (not sure about arm64), > > > > #define __copy_from_user_inatomic __copy_from_user > > > > ie. copy_from_user() minus the access_ok() and memset in the > > !access_ok() path.. but maybe what I want is just the > > pagefault_disable() if that disables copy_from_user() being able to > > block.. > > On a bunch of platforms copy_from_user() starts with might_sleep(); again, > that'll spread to all of the pretty soon. > > Right now those primitives are very badly out of sync; this will change, > but let's not add more PITA sources. That sounds great, as part of discussing this on irc with Rob I too noticed that the the *copy*user* funcs are all rather out of sync. On i915.ko we go full evil mode and pass (faulting) i915 buffer objects in as targets for all these copy*user operations. And for added evilness we have debugfs interfaces to force-unmap/evict these bo, which is used to make sure that the fault handling in slow-paths (after dropping locks and reacquiring them) also works - some of i915 code has slow-slow path fallbacks ;-) Oh and we have a debugfs knob to disable the prefaulting we do, since without those the race is way too small. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
