Steven Rostedt wrote: > The subject forgot to add "RT" in the brackets. > > On Fri, 29 Aug 2008, Andi Kleen wrote: > > >>> I could just force all of the seqbegins to hit the slowpath by hacking >>> the code and see what happens (aside from slowing down, of course ;) >>> >> Only if you don't believe it will really crash? I think it's pretty >> clear even without trying it. >> >> >>> Question: Which seqlock_t does userspace use? I assume it uses >>> seqlock_t and not raw_seqlock_t. >>> >>> But the only reason that I ask is that >>> I converted raw_seqlock_t to use the new style as well to be consistent, >>> >> There's no raw_seqlock_t anywhere in mainline? >> > > Nope, raw_seqlock_t in -rt is equivelant to seqlock_t in mainline. > > >> Anyways the variable is declared (in mainline) in asm-x86/vgtod.h >> >> >>> even though it is not strictly necessary for the same reasons. So if >>> perchance userspace uses the raw variant, I could solve this issue by >>> only re-working the seqlock_t variant. Kind of a long shot, but figured >>> I would mention it :) >>> >> I guess you could define a new seqlock_t which is explicitely user space >> safe. That might avoid such issues in the future. But then >> that would likely require some code duplication and be ugly. >> >> On the other hand whatever problem you fixing in the kernel >> (to be honest it's still unclear to me what the problem is) >> needs to be likely fixed for the userland lock too. >> > > I'm not convinced that the raw_seqlocks (mainline normal seqlocks) has a > problem anyway. > (continuing from IRC) Agreed. I converted them to be consistent. Steve just told me that userspace actually uses the raw_seqlock_t variant, so the answer is simple. Just leave raw_seqlock_t alone and the patch will work fine. Thoughts? -Greg
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