On 03/16/2018 10:33 AM, Alexey Brodkin wrote: > Hi Peter, Vineet, > > On Wed, 2018-03-14 at 18:53 +0100, Peter Zijlstra wrote: >> On Wed, Mar 14, 2018 at 09:58:19AM -0700, Vineet Gupta wrote: >> >>> Well it is broken wrt the semantics the syscall is supposed to provide. >>> Preemption disabling is what prevents a concurrent thread from coming in and >>> modifying the same location (Imagine a variable which is being cmpxchg >>> concurrently by 2 threads). >>> >>> One approach is to do it the MIPS way, emulate the llsc flag - set it under >>> preemption disabled section and clear it in switch_to >> *shudder*... just catch the -EFAULT, force the write fault and retry. > More I look at this initially quite simple thing more it looks like > a can of worms... > I'd say just bite the bullet, write the patch and we can refine it there ! -Vineet
