* Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote: > On Fri, 2012-10-26 at 15:50 +0200, Ingo Molnar wrote: > > > > Oh, just found the reason: > > > > the ptep_modify_prot_start()/modify()/commit() sequence is > > SMP-unsafe - it has to be done under the mmap_sem > > write-locked. > > > > It is safe against *hardware* updates to the PTE, but not > > safe against itself. > > Shouldn't the pte_lock serialize all that still? All sites > that modify PTE contents should hold the pte_lock (and do > afaict). Hm, indeed. Is there no code under down_read() (in the page fault path) that modifies the pte via just pure atomics? Thanks, Ingo -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>